draft-ietf-trans-rfc6962-bis-24.txt   draft-ietf-trans-rfc6962-bis-25.txt 
TRANS (Public Notary Transparency) B. Laurie TRANS (Public Notary Transparency) B. Laurie
Internet-Draft A. Langley Internet-Draft A. Langley
Obsoletes: 6962 (if approved) E. Kasper Obsoletes: 6962 (if approved) E. Kasper
Intended status: Standards Track E. Messeri Intended status: Standards Track E. Messeri
Expires: July 2, 2017 Google Expires: January 1, 2018 Google
R. Stradling R. Stradling
Comodo Comodo
December 29, 2016 June 30, 2017
Certificate Transparency Version 2.0 Certificate Transparency Version 2.0
draft-ietf-trans-rfc6962-bis-24 draft-ietf-trans-rfc6962-bis-25
Abstract Abstract
This document describes version 2.0 of the Certificate Transparency This document describes version 2.0 of the Certificate Transparency
(CT) protocol for publicly logging the existence of Transport Layer (CT) protocol for publicly logging the existence of Transport Layer
Security (TLS) server certificates as they are issued or observed, in Security (TLS) server certificates as they are issued or observed, in
a manner that allows anyone to audit certification authority (CA) a manner that allows anyone to audit certification authority (CA)
activity and notice the issuance of suspect certificates as well as activity and notice the issuance of suspect certificates as well as
to audit the certificate logs themselves. The intent is that to audit the certificate logs themselves. The intent is that
eventually clients would refuse to honor certificates that do not eventually clients would refuse to honor certificates that do not
skipping to change at page 1, line 45 skipping to change at page 1, line 45
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Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
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time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on July 2, 2017. This Internet-Draft will expire on January 1, 2018.
Copyright Notice Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 5 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 5
1.2. Data Structures . . . . . . . . . . . . . . . . . . . . . 5 1.2. Data Structures . . . . . . . . . . . . . . . . . . . . . 5
1.3. Major Differences from CT 1.0 . . . . . . . . . . . . . . 5 1.3. Major Differences from CT 1.0 . . . . . . . . . . . . . . 5
2. Cryptographic Components . . . . . . . . . . . . . . . . . . 7 2. Cryptographic Components . . . . . . . . . . . . . . . . . . 7
2.1. Merkle Hash Trees . . . . . . . . . . . . . . . . . . . . 7 2.1. Merkle Hash Trees . . . . . . . . . . . . . . . . . . . . 7
2.1.1. Merkle Inclusion Proofs . . . . . . . . . . . . . . . 8 2.1.1. Definition of the Merkle Tree . . . . . . . . . . . . 7
2.1.2. Merkle Consistency Proofs . . . . . . . . . . . . . . 9 2.1.2. Verifying a Tree Head Given Entries . . . . . . . . . 8
2.1.3. Example . . . . . . . . . . . . . . . . . . . . . . . 10 2.1.3. Merkle Inclusion Proofs . . . . . . . . . . . . . . . 8
2.1.4. Signatures . . . . . . . . . . . . . . . . . . . . . 11 2.1.4. Merkle Consistency Proofs . . . . . . . . . . . . . . 10
3. Submitters . . . . . . . . . . . . . . . . . . . . . . . . . 11 2.1.5. Example . . . . . . . . . . . . . . . . . . . . . . . 12
3.1. Certificates . . . . . . . . . . . . . . . . . . . . . . 12 2.2. Signatures . . . . . . . . . . . . . . . . . . . . . . . 13
3.2. Precertificates . . . . . . . . . . . . . . . . . . . . . 12 3. Submitters . . . . . . . . . . . . . . . . . . . . . . . . . 13
4. Log Format and Operation . . . . . . . . . . . . . . . . . . 13 3.1. Certificates . . . . . . . . . . . . . . . . . . . . . . 14
4.1. Accepting Submissions . . . . . . . . . . . . . . . . . . 13 3.2. Precertificates . . . . . . . . . . . . . . . . . . . . . 14
4.2. Log Entries . . . . . . . . . . . . . . . . . . . . . . . 14 4. Log Format and Operation . . . . . . . . . . . . . . . . . . 15
4.3. Log ID . . . . . . . . . . . . . . . . . . . . . . . . . 15 4.1. Log Parameters . . . . . . . . . . . . . . . . . . . . . 16
4.4. TransItem Structure . . . . . . . . . . . . . . . . . . . 15 4.2. Accepting Submissions . . . . . . . . . . . . . . . . . . 17
4.5. Merkle Tree Leaves . . . . . . . . . . . . . . . . . . . 17 4.3. Log Entries . . . . . . . . . . . . . . . . . . . . . . . 18
4.6. Signed Certificate Timestamp (SCT) . . . . . . . . . . . 17 4.4. Log ID . . . . . . . . . . . . . . . . . . . . . . . . . 18
4.7. Merkle Tree Head . . . . . . . . . . . . . . . . . . . . 19 4.5. TransItem Structure . . . . . . . . . . . . . . . . . . . 18
4.8. Signed Tree Head (STH) . . . . . . . . . . . . . . . . . 20 4.6. Log Artifact Extensions . . . . . . . . . . . . . . . . . 19
4.9. Merkle Consistency Proofs . . . . . . . . . . . . . . . . 20 4.7. Merkle Tree Leaves . . . . . . . . . . . . . . . . . . . 20
4.10. Merkle Inclusion Proofs . . . . . . . . . . . . . . . . . 21 4.8. Signed Certificate Timestamp (SCT) . . . . . . . . . . . 21
4.11. Shutting down a log . . . . . . . . . . . . . . . . . . . 21 4.9. Merkle Tree Head . . . . . . . . . . . . . . . . . . . . 22
5. Log Client Messages . . . . . . . . . . . . . . . . . . . . . 22 4.10. Signed Tree Head (STH) . . . . . . . . . . . . . . . . . 22
5.1. Add Chain to Log . . . . . . . . . . . . . . . . . . . . 24 4.11. Merkle Consistency Proofs . . . . . . . . . . . . . . . . 23
5.2. Add PreCertChain to Log . . . . . . . . . . . . . . . . . 25 4.12. Merkle Inclusion Proofs . . . . . . . . . . . . . . . . . 24
5.3. Retrieve Latest Signed Tree Head . . . . . . . . . . . . 25 4.13. Shutting down a log . . . . . . . . . . . . . . . . . . . 24
5.4. Retrieve Merkle Consistency Proof between Two Signed Tree 5. Log Client Messages . . . . . . . . . . . . . . . . . . . . . 25
Heads . . . . . . . . . . . . . . . . . . . . . . . . . . 25 5.1. Submit Entry to Log . . . . . . . . . . . . . . . . . . . 26
5.2. Retrieve Latest Signed Tree Head . . . . . . . . . . . . 28
5.5. Retrieve Merkle Inclusion Proof from Log by Leaf Hash . . 26 5.3. Retrieve Merkle Consistency Proof between Two Signed Tree
5.6. Retrieve Merkle Inclusion Proof, Signed Tree Head and Heads . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Consistency Proof by Leaf Hash . . . . . . . . . . . . . 27 5.4. Retrieve Merkle Inclusion Proof from Log by Leaf Hash . . 30
5.7. Retrieve Entries and STH from Log . . . . . . . . . . . . 29 5.5. Retrieve Merkle Inclusion Proof, Signed Tree Head and
5.8. Retrieve Accepted Trust Anchors . . . . . . . . . . . . . 30 Consistency Proof by Leaf Hash . . . . . . . . . . . . . 31
6. TLS Servers . . . . . . . . . . . . . . . . . . . . . . . . . 30 5.6. Retrieve Entries and STH from Log . . . . . . . . . . . . 32
6.1. Multiple SCTs . . . . . . . . . . . . . . . . . . . . . . 31 5.7. Retrieve Accepted Trust Anchors . . . . . . . . . . . . . 34
6.2. TransItemList Structure . . . . . . . . . . . . . . . . . 32 6. TLS Servers . . . . . . . . . . . . . . . . . . . . . . . . . 34
6.3. Presenting SCTs, inclusion proofs and STHs . . . . . . . 32 6.1. Multiple SCTs . . . . . . . . . . . . . . . . . . . . . . 35
6.4. Presenting SCTs only . . . . . . . . . . . . . . . . . . 33 6.2. TransItemList Structure . . . . . . . . . . . . . . . . . 35
6.5. transparency_info TLS Extension . . . . . . . . . . . . . 33 6.3. Presenting SCTs, inclusions proofs and STHs . . . . . . . 36
6.6. cached_info TLS Extension . . . . . . . . . . . . . . . . 33 6.4. transparency_info TLS Extension . . . . . . . . . . . . . 36
7. Certification Authorities . . . . . . . . . . . . . . . . . . 33 6.5. cached_info TLS Extension . . . . . . . . . . . . . . . . 36
7.1. Transparency Information X.509v3 Extension . . . . . . . 34 7. Certification Authorities . . . . . . . . . . . . . . . . . . 37
7.1.1. OCSP Response Extension . . . . . . . . . . . . . . . 34 7.1. Transparency Information X.509v3 Extension . . . . . . . 37
7.1.2. Certificate Extension . . . . . . . . . . . . . . . . 34 7.1.1. OCSP Response Extension . . . . . . . . . . . . . . . 37
7.2. TLS Feature Extension . . . . . . . . . . . . . . . . . . 34 7.1.2. Certificate Extension . . . . . . . . . . . . . . . . 37
8. Clients . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 7.2. TLS Feature X.509v3 Extension . . . . . . . . . . . . . . 37
8.1. Metadata . . . . . . . . . . . . . . . . . . . . . . . . 35 8. Clients . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
8.2. TLS Client . . . . . . . . . . . . . . . . . . . . . . . 36 8.1. TLS Client . . . . . . . . . . . . . . . . . . . . . . . 38
8.2.1. Receiving SCTs . . . . . . . . . . . . . . . . . . . 36 8.1.1. Receiving SCTs and inclusion proofs . . . . . . . . . 38
8.2.2. Reconstructing the TBSCertificate . . . . . . . . . . 36 8.1.2. Reconstructing the TBSCertificate . . . . . . . . . . 38
8.2.3. Validating SCTs . . . . . . . . . . . . . . . . . . . 36 8.1.3. Validating SCTs . . . . . . . . . . . . . . . . . . . 39
8.2.4. Validating inclusion proofs . . . . . . . . . . . . . 36 8.1.4. Fetching inclusion proofs . . . . . . . . . . . . . . 39
8.2.5. Evaluating compliance . . . . . . . . . . . . . . . . 37 8.1.5. Validating inclusion proofs . . . . . . . . . . . . . 39
8.2.6. TLS Feature Extension . . . . . . . . . . . . . . . . 37 8.1.6. Evaluating compliance . . . . . . . . . . . . . . . . 40
8.2.7. cached_info TLS Extension . . . . . . . . . . . . . . 37 8.1.7. cached_info TLS Extension . . . . . . . . . . . . . . 40
8.2.8. Handling of Non-compliance . . . . . . . . . . . . . 37 8.2. Monitor . . . . . . . . . . . . . . . . . . . . . . . . . 40
8.3. Monitor . . . . . . . . . . . . . . . . . . . . . . . . . 38 8.3. Auditing . . . . . . . . . . . . . . . . . . . . . . . . 41
8.4. Auditing . . . . . . . . . . . . . . . . . . . . . . . . 39
8.4.1. Verifying an inclusion proof . . . . . . . . . . . . 40
8.4.2. Verifying consistency between two STHs . . . . . . . 40
8.4.3. Verifying root hash given entries . . . . . . . . . . 41
9. Algorithm Agility . . . . . . . . . . . . . . . . . . . . . . 42 9. Algorithm Agility . . . . . . . . . . . . . . . . . . . . . . 42
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 42 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 42
10.1. TLS Extension Type . . . . . . . . . . . . . . . . . . . 42 10.1. TLS Extension Type . . . . . . . . . . . . . . . . . . . 43
10.2. New Entry to the TLS CachedInformationType registry . . 43 10.2. New Entry to the TLS CachedInformationType registry . . 43
10.3. Hash Algorithms . . . . . . . . . . . . . . . . . . . . 43 10.3. Hash Algorithms . . . . . . . . . . . . . . . . . . . . 43
10.3.1. Expert Review guidelines . . . . . . . . . . . . . . 43 10.3.1. Expert Review guidelines . . . . . . . . . . . . . . 43
10.4. Signature Algorithms . . . . . . . . . . . . . . . . . . 43 10.4. Signature Algorithms . . . . . . . . . . . . . . . . . . 43
10.4.1. Expert Review guidelines . . . . . . . . . . . . . . 44 10.4.1. Expert Review guidelines . . . . . . . . . . . . . . 44
10.5. VersionedTransTypes . . . . . . . . . . . . . . . . . . 44 10.5. VersionedTransTypes . . . . . . . . . . . . . . . . . . 44
10.5.1. Expert Review guidelines . . . . . . . . . . . . . . 45 10.5.1. Expert Review guidelines . . . . . . . . . . . . . . 45
10.6. SCT Extensions . . . . . . . . . . . . . . . . . . . . . 46 10.6. Log Artifact Extension Registry . . . . . . . . . . . . 45
10.6.1. Expert Review guidelines . . . . . . . . . . . . . . 46 10.6.1. Expert Review guidelines . . . . . . . . . . . . . . 46
10.7. STH Extensions . . . . . . . . . . . . . . . . . . . . . 46 10.7. Object Identifiers . . . . . . . . . . . . . . . . . . . 46
10.7.1. Expert Review guidelines . . . . . . . . . . . . . . 46 10.7.1. Log ID Registry . . . . . . . . . . . . . . . . . . 46
10.8. Object Identifiers . . . . . . . . . . . . . . . . . . . 47 10.7.2. Expert Review guidelines . . . . . . . . . . . . . . 47
10.8.1. Log ID Registry . . . . . . . . . . . . . . . . . . 47 11. Security Considerations . . . . . . . . . . . . . . . . . . . 47
10.8.2. Expert Review guidelines . . . . . . . . . . . . . . 47
11. Security Considerations . . . . . . . . . . . . . . . . . . . 48
11.1. Misissued Certificates . . . . . . . . . . . . . . . . . 48 11.1. Misissued Certificates . . . . . . . . . . . . . . . . . 48
11.2. Detection of Misissue . . . . . . . . . . . . . . . . . 48 11.2. Detection of Misissue . . . . . . . . . . . . . . . . . 48
11.3. Misbehaving Logs . . . . . . . . . . . . . . . . . . . . 48 11.3. Misbehaving Logs . . . . . . . . . . . . . . . . . . . . 48
11.4. Deterministic Signatures . . . . . . . . . . . . . . . . 49 11.4. Preventing Tracking Clients . . . . . . . . . . . . . . 49
11.5. Multiple SCTs . . . . . . . . . . . . . . . . . . . . . 49 11.5. Multiple SCTs . . . . . . . . . . . . . . . . . . . . . 49
12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 49 12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 49
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 50 13. References . . . . . . . . . . . . . . . . . . . . . . . . . 49
13.1. Normative References . . . . . . . . . . . . . . . . . . 50 13.1. Normative References . . . . . . . . . . . . . . . . . . 50
13.2. Informative References . . . . . . . . . . . . . . . . . 51 13.2. Informative References . . . . . . . . . . . . . . . . . 51
Appendix A. Supporting v1 and v2 simultaneously . . . . . . . . 52 Appendix A. Supporting v1 and v2 simultaneously . . . . . . . . 53
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 53 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 53
1. Introduction 1. Introduction
Certificate transparency aims to mitigate the problem of misissued Certificate Transparency aims to mitigate the problem of misissued
certificates by providing append-only logs of issued certificates. certificates by providing append-only logs of issued certificates.
The logs do not need to be trusted because they are publicly The logs do not need to be trusted because they are publicly
auditable. Anyone may verify the correctness of each log and monitor auditable. Anyone may verify the correctness of each log and monitor
when new certificates are added to it. The logs do not themselves when new certificates are added to it. The logs do not themselves
prevent misissue, but they ensure that interested parties prevent misissue, but they ensure that interested parties
(particularly those named in certificates) can detect such (particularly those named in certificates) can detect such
misissuance. Note that this is a general mechanism that could be misissuance. Note that this is a general mechanism that could be
used for transparently logging any form of binary data, subject to used for transparently logging any form of binary data, subject to
some kind of inclusion criteria. In this document, we only describe some kind of inclusion criteria. In this document, we only describe
its use for public TLS server certificates (i.e., where the inclusion its use for public TLS server certificates (i.e., where the inclusion
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different things to different people, this can be efficiently different things to different people, this can be efficiently
detected by comparing tree roots and consistency proofs. Similarly, detected by comparing tree roots and consistency proofs. Similarly,
other misbehaviors of any log (e.g., issuing signed timestamps for other misbehaviors of any log (e.g., issuing signed timestamps for
certificates they then don't log) can be efficiently detected and certificates they then don't log) can be efficiently detected and
proved to the world at large. proved to the world at large.
1.1. Requirements Language 1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119]. document are to be interpreted as described in [RFC2119].
1.2. Data Structures 1.2. Data Structures
Data structures are defined according to the conventions laid out in Data structures are defined and encoded according to the conventions
Section 4 of [RFC5246]. laid out in Section 4 of [RFC5246].
1.3. Major Differences from CT 1.0 1.3. Major Differences from CT 1.0
This document revises and obsoletes the experimental CT 1.0 [RFC6962] This document revises and obsoletes the experimental CT 1.0 [RFC6962]
protocol, drawing on insights gained from CT 1.0 deployments and on protocol, drawing on insights gained from CT 1.0 deployments and on
feedback from the community. The major changes are: feedback from the community. The major changes are:
o Hash and signature algorithm agility: permitted algorithms are now o Hash and signature algorithm agility: permitted algorithms are now
specified in IANA registries. specified in IANA registries.
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o Merkle tree leaves: the "MerkleTreeLeaf" structure has been o Merkle tree leaves: the "MerkleTreeLeaf" structure has been
replaced by the "TransItem" structure, which eases extensibility replaced by the "TransItem" structure, which eases extensibility
and simplifies the leaf structure by removing one layer of and simplifies the leaf structure by removing one layer of
abstraction. abstraction.
o Unified leaf format: the structure for both certificate and o Unified leaf format: the structure for both certificate and
precertificate entries now includes only the TBSCertificate precertificate entries now includes only the TBSCertificate
(whereas certificate entries in [RFC6962] included the entire (whereas certificate entries in [RFC6962] included the entire
certificate). certificate).
o SCT extensions: these are now typed and managed by an IANA o Log Artifact Extensions: these are now typed and managed by an
registry. IANA registry, and they can now appear not only in SCTs but also
in STHs.
o STH extensions: STHs can now contain extensions, which are typed
and managed by an IANA registry.
o API outputs: complete "TransItem" structures are returned, rather o API outputs: complete "TransItem" structures are returned, rather
than the constituent parts of each structure. than the constituent parts of each structure.
o get-all-by-hash: new client API for obtaining an inclusion proof o get-all-by-hash: new client API for obtaining an inclusion proof
and the corresponding consistency proof at the same time. and the corresponding consistency proof at the same time.
o Presenting SCTs with proofs: TLS servers may present SCTs together o Presenting SCTs with proofs: TLS servers may present SCTs together
with the corresponding inclusion proofs using any of the with the corresponding inclusion proofs using any of the
mechanisms that [RFC6962] defined for presenting SCTs only. mechanisms that [RFC6962] defined for presenting SCTs only.
(Presenting SCTs only is still supported). (Presenting SCTs only is still supported).
o CT TLS extension: the "signed_certificate_timestamp" TLS extension o CT TLS extension: the "signed_certificate_timestamp" TLS extension
has been replaced by the "transparency_info" TLS extension. has been replaced by the "transparency_info" TLS extension.
o Other TLS extensions: "status_request_v2" may be used (in the same o Other TLS extensions: "status_request_v2" may be used (in the same
manner as "status_request"); "cached_info" may be used to avoid manner as "status_request"); "cached_info" may be used to avoid
sending the same complete SCTs and inclusion proofs to the same sending the same complete SCTs and inclusion proofs to the same
TLS clients multiple times. TLS clients multiple times.
o TLS Feature extension: this certificate extension may be used by a
CA to indicate that CT compliance is required.
o Verification algorithms: added detailed algorithms for verifying o Verification algorithms: added detailed algorithms for verifying
inclusion proofs, for verifying consistency between two STHs, and inclusion proofs, for verifying consistency between two STHs, and
for verifying a root hash given a complete list of the relevant for verifying a root hash given a complete list of the relevant
leaf input entries. leaf input entries.
o Extensive clarifications and editorial work. o Extensive clarifications and editorial work.
2. Cryptographic Components 2. Cryptographic Components
2.1. Merkle Hash Trees 2.1. Merkle Hash Trees
Logs use a binary Merkle Hash Tree for efficient auditing. The 2.1.1. Definition of the Merkle Tree
hashing algorithm used by each log is expected to be specified as
part of the metadata relating to that log (see Section 8.1). We have The log uses a binary Merkle Hash Tree for efficient auditing. The
established a registry of acceptable algorithms, see Section 10.3. hash algorithm used is one of the log's parameters (see Section 4.1).
The hashing algorithm in use is referred to as HASH throughout this We have established a registry of acceptable hash algorithms (see
document and the size of its output in bytes as HASH_SIZE. The input Section 10.3). Throughout this document, the hash algorithm in use
to the Merkle Tree Hash is a list of data entries; these entries will is referred to as HASH and the size of its output in bytes as
be hashed to form the leaves of the Merkle Hash Tree. The output is HASH_SIZE. The input to the Merkle Tree Hash is a list of data
a single HASH_SIZE Merkle Tree Hash. Given an ordered list of n entries; these entries will be hashed to form the leaves of the
inputs, D[n] = {d(0), d(1), ..., d(n-1)}, the Merkle Tree Hash (MTH) Merkle Hash Tree. The output is a single HASH_SIZE Merkle Tree Hash.
is thus defined as follows: Given an ordered list of n inputs, D_n = {d[0], d[1], ..., d[n-1]},
the Merkle Tree Hash (MTH) is thus defined as follows:
The hash of an empty list is the hash of an empty string: The hash of an empty list is the hash of an empty string:
MTH({}) = HASH(). MTH({}) = HASH().
The hash of a list with one entry (also known as a leaf hash) is: The hash of a list with one entry (also known as a leaf hash) is:
MTH({d(0)}) = HASH(0x00 || d(0)). MTH({d[0]}) = HASH(0x00 || d[0]).
For n > 1, let k be the largest power of two smaller than n (i.e., k For n > 1, let k be the largest power of two smaller than n (i.e., k
< n <= 2k). The Merkle Tree Hash of an n-element list D[n] is then < n <= 2k). The Merkle Tree Hash of an n-element list D_n is then
defined recursively as defined recursively as
MTH(D[n]) = HASH(0x01 || MTH(D[0:k]) || MTH(D[k:n])), MTH(D_n) = HASH(0x01 || MTH(D[0:k]) || MTH(D[k:n])),
where || is concatenation and D[k1:k2] denotes the list {d(k1), Where || is concatenation and D[k1:k2] = D'_(k2-k1) denotes the list
d(k1+1), ..., d(k2-1)} of length (k2 - k1). (Note that the hash {d'[0] = d[k1], d'[1] = d[k1+1], ..., d'[k2-k1-1] = d[k2-1]} of
calculations for leaves and nodes differ. This domain separation is length (k2 - k1). (Note that the hash calculations for leaves and
required to give second preimage resistance.) nodes differ; this domain separation is required to give second
preimage resistance).
Note that we do not require the length of the input list to be a Note that we do not require the length of the input list to be a
power of two. The resulting Merkle Tree may thus not be balanced; power of two. The resulting Merkle Tree may thus not be balanced;
however, its shape is uniquely determined by the number of leaves. however, its shape is uniquely determined by the number of leaves.
(Note: This Merkle Tree is essentially the same as the history tree (Note: This Merkle Tree is essentially the same as the history tree
[CrosbyWallach] proposal, except our definition handles non-full [CrosbyWallach] proposal, except our definition handles non-full
trees differently.) trees differently).
2.1.1. Merkle Inclusion Proofs 2.1.2. Verifying a Tree Head Given Entries
When a client has a complete list of n input "entries" from "0" up to
"tree_size - 1" and wishes to verify this list against a tree head
"root_hash" returned by the log for the same "tree_size", the
following algorithm may be used:
1. Set "stack" to an empty stack.
2. For each "i" from "0" up to "tree_size - 1":
1. Push "HASH(0x00 || entries[i])" to "stack".
2. Set "merge_count" to the lowest value ("0" included) such
that "LSB(i >> merge_count)" is not set. In other words, set
"merge_count" to the number of consecutive "1"s found
starting at the least significant bit of "i".
3. Repeat "merge_count" times:
1. Pop "right" from "stack".
2. Pop "left" from "stack".
3. Push "HASH(0x01 || left || right)" to "stack".
3. If there is more than one element in the "stack", repeat the same
merge procedure (Step 2.3 above) until only a single element
remains.
4. The remaining element in "stack" is the Merkle Tree hash for the
given "tree_size" and should be compared by equality against the
supplied "root_hash".
2.1.3. Merkle Inclusion Proofs
A Merkle inclusion proof for a leaf in a Merkle Hash Tree is the A Merkle inclusion proof for a leaf in a Merkle Hash Tree is the
shortest list of additional nodes in the Merkle Tree required to shortest list of additional nodes in the Merkle Tree required to
compute the Merkle Tree Hash for that tree. Each node in the tree is compute the Merkle Tree Hash for that tree. Each node in the tree is
either a leaf node or is computed from the two nodes immediately either a leaf node or is computed from the two nodes immediately
below it (i.e., towards the leaves). At each step up the tree below it (i.e., towards the leaves). At each step up the tree
(towards the root), a node from the inclusion proof is combined with (towards the root), a node from the inclusion proof is combined with
the node computed so far. In other words, the inclusion proof the node computed so far. In other words, the inclusion proof
consists of the list of missing nodes required to compute the nodes consists of the list of missing nodes required to compute the nodes
leading from a leaf to the root of the tree. If the root computed leading from a leaf to the root of the tree. If the root computed
from the inclusion proof matches the true root, then the inclusion from the inclusion proof matches the true root, then the inclusion
proof proves that the leaf exists in the tree. proof proves that the leaf exists in the tree.
Given an ordered list of n inputs to the tree, D[n] = {d(0), ..., 2.1.3.1. Generating an Inclusion Proof
d(n-1)}, the Merkle inclusion proof PATH(m, D[n]) for the (m+1)th
input d(m), 0 <= m < n, is defined as follows: Given an ordered list of n inputs to the tree, D_n = {d[0], d[1],
..., d[n-1]}, the Merkle inclusion proof PATH(m, D_n) for the (m+1)th
input d[m], 0 <= m < n, is defined as follows:
The proof for the single leaf in a tree with a one-element input list The proof for the single leaf in a tree with a one-element input list
D[1] = {d(0)} is empty: D[1] = {d[0]} is empty:
PATH(0, {d(0)}) = {} PATH(0, {d[0]}) = {}
For n > 1, let k be the largest power of two smaller than n. The For n > 1, let k be the largest power of two smaller than n. The
proof for the (m+1)th element d(m) in a list of n > m elements is proof for the (m+1)th element d[m] in a list of n > m elements is
then defined recursively as then defined recursively as
PATH(m, D[n]) = PATH(m, D[0:k]) : MTH(D[k:n]) for m < k; and PATH(m, D_n) = PATH(m, D[0:k]) : MTH(D[k:n]) for m < k; and
PATH(m, D[n]) = PATH(m - k, D[k:n]) : MTH(D[0:k]) for m >= k, PATH(m, D_n) = PATH(m - k, D[k:n]) : MTH(D[0:k]) for m >= k,
where : is concatenation of lists and D[k1:k2] denotes the length (k2 The : operator and D[k1:k2] are defined the same as in Section 2.1.1.
- k1) list {d(k1), d(k1+1),..., d(k2-1)} as before.
2.1.2. Merkle Consistency Proofs 2.1.3.2. Verifying an Inclusion Proof
When a client has received an inclusion proof (e.g., in a "TransItem"
of type "inclusion_proof_v2") and wishes to verify inclusion of an
input "hash" for a given "tree_size" and "root_hash", the following
algorithm may be used to prove the "hash" was included in the
"root_hash":
1. Compare "leaf_index" against "tree_size". If "leaf_index" is
greater than or equal to "tree_size" then fail the proof
verification.
2. Set "fn" to "leaf_index" and "sn" to "tree_size - 1".
3. Set "r" to "hash".
4. For each value "p" in the "inclusion_path" array:
If "sn" is 0, stop the iteration and fail the proof verification.
If "LSB(fn)" is set, or if "fn" is equal to "sn", then:
1. Set "r" to "HASH(0x01 || p || r)"
2. If "LSB(fn)" is not set, then right-shift both "fn" and "sn"
equally until either "LSB(fn)" is set or "fn" is "0".
Otherwise:
1. Set "r" to "HASH(0x01 || r || p)"
Finally, right-shift both "fn" and "sn" one time.
5. Compare "sn" to 0. Compare "r" against the "root_hash". If "sn"
is equal to 0, and "r" and the "root_hash" are equal, then the
log has proven the inclusion of "hash". Otherwise, fail the
proof verification.
2.1.4. Merkle Consistency Proofs
Merkle consistency proofs prove the append-only property of the tree. Merkle consistency proofs prove the append-only property of the tree.
A Merkle consistency proof for a Merkle Tree Hash MTH(D[n]) and a A Merkle consistency proof for a Merkle Tree Hash MTH(D_n) and a
previously advertised hash MTH(D[0:m]) of the first m leaves, m <= n, previously advertised hash MTH(D[0:m]) of the first m leaves, m <= n,
is the list of nodes in the Merkle Tree required to verify that the is the list of nodes in the Merkle Tree required to verify that the
first m inputs D[0:m] are equal in both trees. Thus, a consistency first m inputs D[0:m] are equal in both trees. Thus, a consistency
proof must contain a set of intermediate nodes (i.e., commitments to proof must contain a set of intermediate nodes (i.e., commitments to
inputs) sufficient to verify MTH(D[n]), such that (a subset of) the inputs) sufficient to verify MTH(D_n), such that (a subset of) the
same nodes can be used to verify MTH(D[0:m]). We define an algorithm same nodes can be used to verify MTH(D[0:m]). We define an algorithm
that outputs the (unique) minimal consistency proof. that outputs the (unique) minimal consistency proof.
Given an ordered list of n inputs to the tree, D[n] = {d(0), ..., 2.1.4.1. Generating a Consistency Proof
d(n-1)}, the Merkle consistency proof PROOF(m, D[n]) for a previous
Merkle Tree Hash MTH(D[0:m]), 0 < m < n, is defined as:
PROOF(m, D[n]) = SUBPROOF(m, D[n], true) Given an ordered list of n inputs to the tree, D_n = {d[0], d[1],
..., d[n-1]}, the Merkle consistency proof PROOF(m, D_n) for a
previous Merkle Tree Hash MTH(D[0:m]), 0 < m < n, is defined as:
PROOF(m, D_n) = SUBPROOF(m, D_n, true)
In SUBPROOF, the boolean value represents whether the subtree created In SUBPROOF, the boolean value represents whether the subtree created
from D[0:m] is a complete subtree of the Merkle Tree created from from D[0:m] is a complete subtree of the Merkle Tree created from
D[n], and, consequently, whether the subtree Merkle Tree Hash D_n, and, consequently, whether the subtree Merkle Tree Hash
MTH(D[0:m]) is known. The initial call to SUBPROOF sets this to be MTH(D[0:m]) is known. The initial call to SUBPROOF sets this to be
true, and SUBPROOF is then defined as follows: true, and SUBPROOF is then defined as follows:
The subproof for m = n is empty if m is the value for which PROOF was The subproof for m = n is empty if m is the value for which PROOF was
originally requested (meaning that the subtree created from D[0:m] is originally requested (meaning that the subtree created from D[0:m] is
a complete subtree of the Merkle Tree created from the original D[n] a complete subtree of the Merkle Tree created from the original D_n
for which PROOF was requested, and the subtree Merkle Tree Hash for which PROOF was requested, and the subtree Merkle Tree Hash
MTH(D[0:m]) is known): MTH(D[0:m]) is known):
SUBPROOF(m, D[m], true) = {} SUBPROOF(m, D[m], true) = {}
Otherwise, the subproof for m = n is the Merkle Tree Hash committing Otherwise, the subproof for m = n is the Merkle Tree Hash committing
inputs D[0:m]: inputs D[0:m]:
SUBPROOF(m, D[m], false) = {MTH(D[m])} SUBPROOF(m, D[m], false) = {MTH(D[m])}
For m < n, let k be the largest power of two smaller than n. The For m < n, let k be the largest power of two smaller than n. The
subproof is then defined recursively. subproof is then defined recursively.
If m <= k, the right subtree entries D[k:n] only exist in the current If m <= k, the right subtree entries D[k:n] only exist in the current
tree. We prove that the left subtree entries D[0:k] are consistent tree. We prove that the left subtree entries D[0:k] are consistent
and add a commitment to D[k:n]: and add a commitment to D[k:n]:
SUBPROOF(m, D[n], b) = SUBPROOF(m, D[0:k], b) : MTH(D[k:n]) SUBPROOF(m, D_n, b) = SUBPROOF(m, D[0:k], b) : MTH(D[k:n])
If m > k, the left subtree entries D[0:k] are identical in both If m > k, the left subtree entries D[0:k] are identical in both
trees. We prove that the right subtree entries D[k:n] are consistent trees. We prove that the right subtree entries D[k:n] are consistent
and add a commitment to D[0:k]. and add a commitment to D[0:k].
SUBPROOF(m, D[n], b) = SUBPROOF(m - k, D[k:n], false) : MTH(D[0:k]) SUBPROOF(m, D_n, b) = SUBPROOF(m - k, D[k:n], false) : MTH(D[0:k])
Here, : is a concatenation of lists, and D[k1:k2] denotes the length
(k2 - k1) list {d(k1), d(k1+1),..., d(k2-1)} as before.
The number of nodes in the resulting proof is bounded above by The number of nodes in the resulting proof is bounded above by
ceil(log2(n)) + 1. ceil(log2(n)) + 1.
2.1.3. Example The : operator and D[k1:k2] are defined the same as in Section 2.1.1.
2.1.4.2. Verifying Consistency between Two Tree Heads
When a client has a tree head "first_hash" for tree size "first", a
tree head "second_hash" for tree size "second" where "0 < first <
second", and has received a consistency proof between the two (e.g.,
in a "TransItem" of type "consistency_proof_v2"), the following
algorithm may be used to verify the consistency proof:
1. If "first" is an exact power of 2, then prepend "first_hash" to
the "consistency_path" array.
2. Set "fn" to "first - 1" and "sn" to "second - 1".
3. If "LSB(fn)" is set, then right-shift both "fn" and "sn" equally
until "LSB(fn)" is not set.
4. Set both "fr" and "sr" to the first value in the
"consistency_path" array.
5. For each subsequent value "c" in the "consistency_path" array:
If "sn" is 0, stop the iteration and fail the proof verification.
If "LSB(fn)" is set, or if "fn" is equal to "sn", then:
1. Set "fr" to "HASH(0x01 || c || fr)"
Set "sr" to "HASH(0x01 || c || sr)"
2. If "LSB(fn)" is not set, then right-shift both "fn" and "sn"
equally until either "LSB(fn)" is set or "fn" is "0".
Otherwise:
1. Set "sr" to "HASH(0x01 || sr || c)"
Finally, right-shift both "fn" and "sn" one time.
6. After completing iterating through the "consistency_path" array
as described above, verify that the "fr" calculated is equal to
the "first_hash" supplied, that the "sr" calculated is equal to
the "second_hash" supplied and that "sn" is 0.
2.1.5. Example
The binary Merkle Tree with 7 leaves: The binary Merkle Tree with 7 leaves:
hash hash
/ \ / \
/ \ / \
/ \ / \
/ \ / \
/ \ / \
k l k l
skipping to change at page 11, line 42 skipping to change at page 13, line 42
d, g, l]. c, g are used to verify hash0, and d, l are additionally d, g, l]. c, g are used to verify hash0, and d, l are additionally
used to show hash is consistent with hash0. used to show hash is consistent with hash0.
The consistency proof between hash1 and hash is PROOF(4, D[7]) = [l]. The consistency proof between hash1 and hash is PROOF(4, D[7]) = [l].
hash can be verified using hash1=k and l. hash can be verified using hash1=k and l.
The consistency proof between hash2 and hash is PROOF(6, D[7]) = [i, The consistency proof between hash2 and hash is PROOF(6, D[7]) = [i,
j, k]. k, i are used to verify hash2, and j is additionally used to j, k]. k, i are used to verify hash2, and j is additionally used to
show hash is consistent with hash2. show hash is consistent with hash2.
2.1.4. Signatures 2.2. Signatures
Various data structures are signed. A log MUST use one of the Various data structures Section 1.2 are signed. A log MUST use one
signature algorithms defined in Section 10.4. of the signature algorithms defined in Section 10.4.
3. Submitters 3. Submitters
Submitters submit certificates or preannouncements of certificates Submitters submit certificates or preannouncements of certificates
prior to issuance (precertificates) to logs for public auditing, as prior to issuance (precertificates) to logs for public auditing, as
described below. In order to enable attribution of each logged described below. In order to enable attribution of each logged
certificate or precertificate to its issuer, each submission MUST be certificate or precertificate to its issuer, each submission MUST be
accompanied by all additional certificates required to verify the accompanied by all additional certificates required to verify the
chain up to an accepted trust anchor. The trust anchor (a root or chain up to an accepted trust anchor. The trust anchor (a root or
intermediate CA certificate) MAY be omitted from the submission. intermediate CA certificate) MAY be omitted from the submission.
If a log accepts a submission, it will return a Signed Certificate If a log accepts a submission, it will return a Signed Certificate
Timestamp (SCT) (see Section 4.6). The submitter SHOULD validate the Timestamp (SCT) (see Section 4.8). The submitter SHOULD validate the
returned SCT as described in Section 8.2 if they understand its returned SCT as described in Section 8.1 if they understand its
format and they intend to use it directly in a TLS handshake or to format and they intend to use it directly in a TLS handshake or to
construct a certificate. If the submitter does not need the SCT (for construct a certificate. If the submitter does not need the SCT (for
example, the certificate is being submitted simply to make it example, the certificate is being submitted simply to make it
available in the log), it MAY validate the SCT. available in the log), it MAY validate the SCT.
3.1. Certificates 3.1. Certificates
Any entity can submit a certificate (Section 5.1) to a log. Since it Any entity can submit a certificate (Section 5.1) to a log. Since it
is anticipated that TLS clients will reject certificates that are not is anticipated that TLS clients will reject certificates that are not
logged, it is expected that certificate issuers and subjects will be logged, it is expected that certificate issuers and subjects will be
strongly motivated to submit them. strongly motivated to submit them.
3.2. Precertificates 3.2. Precertificates
CAs may preannounce a certificate prior to issuance by submitting a CAs may preannounce a certificate prior to issuance by submitting a
precertificate (Section 5.2) that the log can use to create an entry precertificate (Section 5.1) that the log can use to create an entry
that will be valid against the issued certificate. The CA MAY that will be valid against the issued certificate. The CA MAY
incorporate the returned SCT in the issued certificate. One example incorporate the returned SCT in the issued certificate. One example
of where the returned SCT is not incorporated in the issued of where the returned SCT is not incorporated in the issued
certificate is when a CA sends the precertificate to multiple logs, certificate is when a CA sends the precertificate to multiple logs,
but only incorporates the SCTs that are returned first. but only incorporates the SCTs that are returned first.
A precertificate is a CMS [RFC5652] "signed-data" object that A precertificate is a CMS [RFC5652] "signed-data" object that
conforms to the following requirements: conforms to the following profile:
o It MUST be DER encoded. o It MUST be DER encoded.
o "SignedData.encapContentInfo.eContentType" MUST be the OID o "SignedData.version" MUST be v3(3).
1.3.101.78.
o "SignedData.encapContentInfo.eContent" MUST contain a o "SignedData.digestAlgorithms" MUST only include the
TBSCertificate [RFC5280] that will be identical to the "SignerInfo.digestAlgorithm" OID value (see below).
TBSCertificate in the issued certificate, except that the
Transparency Information (Section 7.1) extension MUST be omitted.
o "SignedData.signerInfos" MUST contain a signature from the same o "SignedData.encapContentInfo":
(root or intermediate) CA that will ultimately issue the
certificate. This signature indicates the CA's intent to issue
the certificate. This intent is considered binding (i.e.,
misissuance of the precertificate is considered equivalent to
misissuance of the certificate). (Note that, because of the
structure of CMS, the signature on the CMS object will not be a
valid X.509v3 signature and so cannot be used to construct a
certificate from the precertificate).
o "SignedData.certificates" SHOULD be omitted. * "eContentType" MUST be the OID 1.3.101.78.
* "eContent" MUST contain a TBSCertificate [RFC5280] that will be
identical to the TBSCertificate in the issued certificate,
except that the Transparency Information (Section 7.1)
extension MUST be omitted.
o "SignedData.certificates" MUST be omitted.
o "SignedData.crls" MUST be omitted.
o "SignedData.signerInfos" MUST contain one "SignerInfo":
* "version" MUST be v3(3).
* "sid" MUST use the "subjectKeyIdentifier" option.
* "digestAlgorithm" MUST be one of the hash algorithm OIDs listed
in Section 10.3.
* "signedAttrs" MUST be present and MUST contain two attributes:
+ A content-type attribute whose value is the same as
"SignedData.encapContentInfo.eContentType".
+ A message-digest attribute whose value is the message digest
of "SignedData.encapContentInfo.eContent".
* "signatureAlgorithm" MUST be the same OID as
"TBSCertificate.signature".
* "signature" MUST be from the same (root or intermediate) CA
that will ultimately issue the certificate. This signature
indicates the CA's intent to issue the certificate. This
intent is considered binding (i.e., misissuance of the
precertificate is considered equivalent to misissuance of the
corresponding certificate).
* "unsignedAttrs" MUST be omitted.
"SignerInfo.signedAttrs" is included in the message digest
calculation process (see Section 5.4 of [RFC5652]), which ensures
that the "SignerInfo.signature" value will not be a valid X.509v3
signature that could be used in conjunction with the TBSCertificate
(from "SignedData.encapContentInfo.eContent") to construct a valid
certificate.
4. Log Format and Operation 4. Log Format and Operation
A log is a single, append-only Merkle Tree of submitted certificate A log is a single, append-only Merkle Tree of submitted certificate
and precertificate entries. and precertificate entries.
When it receives and accepts a valid submission, the log MUST return When it receives and accepts a valid submission, the log MUST return
an SCT that corresponds to the submitted certificate or an SCT that corresponds to the submitted certificate or
precertificate. If the log has previously seen this valid precertificate. If the log has previously seen this valid
submission, it SHOULD return the same SCT as it returned before (to submission, it SHOULD return the same SCT as it returned before (to
reduce the ability to track clients as described in Section 11.4). reduce the ability to track clients as described in Section 11.4).
If different SCTs are produced for the same submission, multiple log If different SCTs are produced for the same submission, multiple log
entries will have to be created, one for each SCT (as the timestamp entries will have to be created, one for each SCT (as the timestamp
is a part of the leaf structure). Note that if a certificate was is a part of the leaf structure). Note that if a certificate was
previously logged as a precertificate, then the precertificate's SCT previously logged as a precertificate, then the precertificate's SCT
of type "precert_sct_v2" would not be appropriate; instead, a fresh of type "precert_sct_v2" would not be appropriate; instead, a fresh
SCT of type "x509_sct_v2" should be generated. SCT of type "x509_sct_v2" should be generated.
An SCT is the log's promise to incorporate the submitted entry in its An SCT is the log's promise to append to its Merkle Tree an entry for
Merkle Tree no later than a fixed amount of time, known as the the accepted submission. Upon producing an SCT, the log MUST fulfil
Maximum Merge Delay (MMD), after the issuance of the SCT. this promise by performing the following actions within a fixed
Periodically, the log MUST append all its new entries to its Merkle amount of time known as the Maximum Merge Delay (MMD), which is one
Tree and sign the root of the tree. of the log's parameters (see Section 4.1): * Allocate a tree index to
the entry representing the accepted submission. * Calculate the root
of the tree. * Sign the root of the tree (see Section 4.10). The
log may append multiple entries before signing the root of the tree.
Log operators MUST NOT impose any conditions on retrieving or sharing Log operators SHOULD NOT impose any conditions on retrieving or
data from the log. sharing data from the log.
4.1. Accepting Submissions 4.1. Log Parameters
Before accepting a submitted certificate or precertificate, the log A log is defined by a collection of parameters, which are used by
MUST verify that it has a valid signature chain to an accepted trust clients to communicate with the log and to verify log artifacts.
anchor, using the chain of intermediate CA certificates provided by
the submitter. Logs SHOULD accept certificates and precertificates Base URL: The URL to substitute for <log server> in Section 5.
that are fully valid according to RFC 5280 [RFC5280] verification
rules and are submitted with such a chain (A log may decide, for Hash Algorithm: The hash algorithm used for the Merkle Tree (see
example, to temporarily reject valid submissions to protect itself Section 10.3).
against denial-of-service attacks).
Signature Algorithm: The signature algorithm used (see Section 2.2).
Public Key: The public key used to verify signatures generated by
the log. A log MUST NOT use the same keypair as any other log.
Log ID: The OID that uniquely identifies the log.
Maximum Merge Delay: The MMD the log has committed to.
Version: The version of the protocol supported by the log (currently
1 or 2).
Maximum Chain Length: The longest chain submission the log is
willing to accept, if the log chose to limit it.
STH Frequency Count: The maximum number of STHs the log may produce
in any period equal to the "Maximum Merge Delay" (see
Section 4.10).
Final STH: If a log has been closed down (i.e., no longer accepts
new entries), existing entries may still be valid. In this case,
the client should know the final valid STH in the log to ensure no
new entries can be added without detection. The final STH should
be provided in the form of a TransItem of type
"signed_tree_head_v2".
[JSON.Metadata] is an example of a metadata format which includes the
above elements.
4.2. Accepting Submissions
To avoid being overloaded by invalid submissions, the log MUST NOT
accept any submission until it has verified that the submitted
certificate or precertificate has a valid signature chain to an
accepted trust anchor, using only the chain of intermediate CA
certificates provided by the submitter.
Logs SHOULD accept certificates and precertificates that are fully
valid according to RFC 5280 [RFC5280] verification rules and are
submitted with such a chain. (A log may decide, for example, to
temporarily reject valid submissions to protect itself against
denial-of-service attacks).
Logs MAY accept certificates and precertificates that have expired, Logs MAY accept certificates and precertificates that have expired,
are not yet valid, have been revoked, or are otherwise not fully are not yet valid, have been revoked, or are otherwise not fully
valid according to RFC 5280 verification rules in order to valid according to RFC 5280 verification rules in order to
accommodate quirks of CA certificate-issuing software. However, logs accommodate quirks of CA certificate-issuing software. However, logs
MUST reject submissions without a valid signature chain to an MUST reject submissions without a valid signature chain to an
accepted trust anchor. Logs MUST also reject precertificates that do accepted trust anchor. Logs MUST also reject precertificates that do
not conform to the requirements in Section 3.2. not conform to the requirements in Section 3.2.
Logs SHOULD limit the length of chain they will accept. The maximum Logs SHOULD limit the length of chain they will accept. The maximum
chain length is specified in the log's metadata. chain length is one of the log's parameters (see Section 4.1).
The log SHALL allow retrieval of its list of accepted trust anchors The log SHALL allow retrieval of its list of accepted trust anchors
(see Section 5.8), each of which is a root or intermediate CA (see Section 5.7), each of which is a root or intermediate CA
certificate. This list might usefully be the union of root certificate. This list might usefully be the union of root
certificates trusted by major browser vendors. certificates trusted by major browser vendors.
4.2. Log Entries 4.3. Log Entries
If a submission is accepted and an SCT issued, the accepting log MUST If a submission is accepted and an SCT issued, the accepting log MUST
store the entire chain used for verification. This chain MUST store the entire chain used for verification. This chain MUST
include the certificate or precertificate itself, the zero or more include the certificate or precertificate itself, the zero or more
intermediate CA certificates provided by the submitter, and the trust intermediate CA certificates provided by the submitter, and the trust
anchor used to verify the chain (even if it was omitted from the anchor used to verify the chain (even if it was omitted from the
submission). The log MUST present this chain for auditing upon submission). The log MUST present this chain for auditing upon
request (see Section 5.7). This chain is required to prevent a CA request (see Section 5.6). This prevents the CA from avoiding blame
from avoiding blame by logging a partial or empty chain. by logging a partial or empty chain. Each log entry is a "TransItem"
structure of type "x509_entry_v2" or "precert_entry_v2". However, a
Each certificate entry in a log MUST include a "X509ChainEntry" log may store its entries in any format. If a log does not store
structure, and each precertificate entry MUST include a this "TransItem" in full, it must store the "timestamp" and
"PrecertChainEntryV2" structure: "sct_extensions" of the corresponding
"TimestampedCertificateEntryDataV2" structure. The "TransItem" can
opaque ASN.1Cert<1..2^24-1>; be reconstructed from these fields and the entire chain that the log
used to verify the submission.
struct {
ASN.1Cert leaf_certificate;
ASN.1Cert certificate_chain<0..2^24-1>;
} X509ChainEntry;
opaque CMSPrecert<1..2^24-1>;
struct {
CMSPrecert pre_certificate;
ASN.1Cert precertificate_chain<1..2^24-1>;
} PrecertChainEntryV2;
"leaf_certificate" is a submitted certificate that has been accepted
by the log.
"certificate_chain" is a vector of 0 or more additional certificates
required to verify "leaf_certificate". The first certificate MUST
certify "leaf_certificate". Each following certificate MUST directly
certify the one preceding it. The final certificate MUST be a trust
anchor accepted by the log. If "leaf_certificate" is an accepted
trust anchor, then this vector is empty.
"pre_certificate" is a submitted precertificate that has been
accepted by the log.
"precertificate_chain" is a vector of 1 or more additional
certificates required to verify "pre_certificate". The first
certificate MUST certify "pre_certificate". Each following
certificate MUST directly certify the one preceding it. The final
certificate MUST be a trust anchor accepted by the log.
4.3. Log ID 4.4. Log ID
Each log is identified by an OID, which is specified in the log's Each log is identified by an OID, which is one of the log's
metadata and which MUST NOT be used to identify any other log. A parameters (see Section 4.1) and which MUST NOT be used to identify
log's operator MUST either allocate the OID themselves or request an any other log. A log's operator MUST either allocate the OID
OID from the Log ID Registry (see Section 10.8.1). Various data themselves or request an OID from the Log ID Registry (see
structures include the DER encoding of this OID, excluding the ASN.1 Section 10.7.1). Various data structures include the DER encoding of
tag and length bytes, in an opaque vector: this OID, excluding the ASN.1 tag and length bytes, in an opaque
vector:
opaque LogID<2..127>; opaque LogID<2..127>;
Note that the ASN.1 length and the opaque vector length are identical Note that the ASN.1 length and the opaque vector length are identical
in size (1 byte) and value, so the DER encoding of the OID can be in size (1 byte) and value, so the DER encoding of the OID can be
reproduced simply by prepending an OBJECT IDENTIFIER tag (0x06) to reproduced simply by prepending an OBJECT IDENTIFIER tag (0x06) to
the opaque vector length and contents. the opaque vector length and contents.
OIDs used to identify logs are limited such that the DER encoding of OIDs used to identify logs are limited such that the DER encoding of
their value is less than or equal to 127 octets. their value is less than or equal to 127 octets.
4.4. TransItem Structure 4.5. TransItem Structure
Various data structures are encapsulated in the "TransItem" structure Various data structures are encapsulated in the "TransItem" structure
to ensure that the type and version of each one is identified in a to ensure that the type and version of each one is identified in a
common fashion: common fashion:
enum { enum {
reserved(0), reserved(0),
x509_entry_v2(1), precert_entry_v2(2), x509_entry_v2(1), precert_entry_v2(2),
x509_sct_v2(3), precert_sct_v2(4), x509_sct_v2(3), precert_sct_v2(4),
signed_tree_head_v2(5), consistency_proof_v2(6), signed_tree_head_v2(5), consistency_proof_v2(6),
inclusion_proof_v2(7), x509_sct_with_proof_v2(8), inclusion_proof_v2(7),
precert_sct_with_proof_v2(9),
(65535) (65535)
} VersionedTransType; } VersionedTransType;
struct { struct {
VersionedTransType versioned_type; VersionedTransType versioned_type;
select (versioned_type) { select (versioned_type) {
case x509_entry_v2: TimestampedCertificateEntryDataV2; case x509_entry_v2: TimestampedCertificateEntryDataV2;
case precert_entry_v2: TimestampedCertificateEntryDataV2; case precert_entry_v2: TimestampedCertificateEntryDataV2;
case x509_sct_v2: SignedCertificateTimestampDataV2; case x509_sct_v2: SignedCertificateTimestampDataV2;
case precert_sct_v2: SignedCertificateTimestampDataV2; case precert_sct_v2: SignedCertificateTimestampDataV2;
case signed_tree_head_v2: SignedTreeHeadDataV2; case signed_tree_head_v2: SignedTreeHeadDataV2;
case consistency_proof_v2: ConsistencyProofDataV2; case consistency_proof_v2: ConsistencyProofDataV2;
case inclusion_proof_v2: InclusionProofDataV2; case inclusion_proof_v2: InclusionProofDataV2;
case x509_sct_with_proof_v2: SCTWithProofDataV2;
case precert_sct_with_proof_v2: SCTWithProofDataV2;
} data; } data;
} TransItem; } TransItem;
"versioned_type" is a value from the IANA registry in Section 10.5 "versioned_type" is a value from the IANA registry in Section 10.5
that identifies the type of the encapsulated data structure and the that identifies the type of the encapsulated data structure and the
earliest version of this protocol to which it conforms. This earliest version of this protocol to which it conforms. This
document is v2. document is v2.
"data" is the encapsulated data structure. The various structures "data" is the encapsulated data structure. The various structures
named with the "DataV2" suffix are defined in later sections of this named with the "DataV2" suffix are defined in later sections of this
skipping to change at page 17, line 5 skipping to change at page 19, line 47
enumerations "Version", "LogEntryType", "SignatureType" and enumerations "Version", "LogEntryType", "SignatureType" and
"MerkleLeafType". Note also that v1 did not define "TransItem", but "MerkleLeafType". Note also that v1 did not define "TransItem", but
this document provides guidelines (see Appendix A) on how v2 this document provides guidelines (see Appendix A) on how v2
implementations can co-exist with v1 implementations. implementations can co-exist with v1 implementations.
Future versions of this protocol may reuse "VersionedTransType" Future versions of this protocol may reuse "VersionedTransType"
values defined in this document as long as the corresponding data values defined in this document as long as the corresponding data
structures are not modified, and may add new "VersionedTransType" structures are not modified, and may add new "VersionedTransType"
values for new or modified data structures. values for new or modified data structures.
4.5. Merkle Tree Leaves 4.6. Log Artifact Extensions
enum {
reserved(65535)
} ExtensionType;
struct {
ExtensionType extension_type;
opaque extension_data<0..2^16-1>;
} Extension;
The "Extension" structure provides a generic extensibility for log
artifacts, including Signed Certificate Timestamps (Section 4.8) and
Signed Tree Heads (Section 4.10). The interpretation of the
"extension_data" field is determined solely by the value of the
"extension_type" field.
This document does not define any extensions, but it does establish a
registry for future "ExtensionType" values (see Section 10.6). Each
document that registers a new "ExtensionType" must specify the
context in which it may be used (e.g., SCT, STH, or both) and
describe how to interpret the corresponding "extension_data".
4.7. Merkle Tree Leaves
The leaves of a log's Merkle Tree correspond to the log's entries The leaves of a log's Merkle Tree correspond to the log's entries
(see Section 4.2). Each leaf is the leaf hash (Section 2.1) of a (see Section 4.3). Each leaf is the leaf hash (Section 2.1) of a
"TransItem" structure of type "x509_entry_v2" or "precert_entry_v2", "TransItem" structure of type "x509_entry_v2" or "precert_entry_v2",
which encapsulates a "TimestampedCertificateEntryDataV2" structure. which encapsulates a "TimestampedCertificateEntryDataV2" structure.
Note that leaf hashes are calculated as HASH(0x00 || TransItem), Note that leaf hashes are calculated as HASH(0x00 || TransItem),
where the hashing algorithm is specified in the log's metadata. where the hash algorithm is one of the log's parameters.
opaque TBSCertificate<1..2^24-1>; opaque TBSCertificate<1..2^24-1>;
struct { struct {
uint64 timestamp; uint64 timestamp;
opaque issuer_key_hash<32..2^8-1>; opaque issuer_key_hash<32..2^8-1>;
TBSCertificate tbs_certificate; TBSCertificate tbs_certificate;
SctExtension sct_extensions<0..2^16-1>; Extension sct_extensions<0..2^16-1>;
} TimestampedCertificateEntryDataV2; } TimestampedCertificateEntryDataV2;
"timestamp" is the NTP Time [RFC5905] at which the certificate or "timestamp" is the NTP Time [RFC5905] at which the certificate or
precertificate was accepted by the log, measured in milliseconds precertificate was accepted by the log, measured in milliseconds
since the epoch (January 1, 1970, 00:00 UTC), ignoring leap seconds. since the epoch (January 1, 1970, 00:00 UTC), ignoring leap seconds.
Note that the leaves of a log's Merkle Tree are not required to be in Note that the leaves of a log's Merkle Tree are not required to be in
strict chronological order. strict chronological order.
"issuer_key_hash" is the HASH of the public key of the CA that issued "issuer_key_hash" is the HASH of the public key of the CA that issued
the certificate or precertificate, calculated over the DER encoding the certificate or precertificate, calculated over the DER encoding
of the key represented as SubjectPublicKeyInfo [RFC5280]. This is of the key represented as SubjectPublicKeyInfo [RFC5280]. This is
needed to bind the CA to the certificate or precertificate, making it needed to bind the CA to the certificate or precertificate, making it
impossible for the corresponding SCT to be valid for any other impossible for the corresponding SCT to be valid for any other
certificate or precertificate whose TBSCertificate matches certificate or precertificate whose TBSCertificate matches
"tbs_certificate". The length of the "issuer_key_hash" MUST match "tbs_certificate". The length of the "issuer_key_hash" MUST match
HASH_SIZE. HASH_SIZE.
"tbs_certificate" is the DER encoded TBSCertificate from either the "tbs_certificate" is the DER encoded TBSCertificate from the
"leaf_certificate" (in the case of an "X509ChainEntry") or the submission. (Note that a precertificate's TBSCertificate can be
"pre_certificate" (in the case of a "PrecertChainEntryV2"). (Note reconstructed from the corresponding certificate as described in
that a precertificate's TBSCertificate can be reconstructed from the Section 8.1.2).
corresponding certificate as described in Section 8.2.2).
"sct_extensions" matches the SCT extensions of the corresponding SCT. "sct_extensions" matches the SCT extensions of the corresponding SCT.
4.6. Signed Certificate Timestamp (SCT) The type of the "TransItem" corresponds to the value of the "type"
parameter supplied in the Section 5.1 call.
4.8. Signed Certificate Timestamp (SCT)
An SCT is a "TransItem" structure of type "x509_sct_v2" or An SCT is a "TransItem" structure of type "x509_sct_v2" or
"precert_sct_v2", which encapsulates a "precert_sct_v2", which encapsulates a
"SignedCertificateTimestampDataV2" structure: "SignedCertificateTimestampDataV2" structure:
enum {
reserved(65535)
} SctExtensionType;
struct {
SctExtensionType sct_extension_type;
opaque sct_extension_data<0..2^16-1>;
} SctExtension;
struct { struct {
LogID log_id; LogID log_id;
uint64 timestamp; uint64 timestamp;
SctExtension sct_extensions<0..2^16-1>; Extension sct_extensions<0..2^16-1>;
digitally-signed struct { opaque signature<0..2^16-1>;
TransItem timestamped_entry;
} signature;
} SignedCertificateTimestampDataV2; } SignedCertificateTimestampDataV2;
"log_id" is this log's unique ID, encoded in an opaque vector as "log_id" is this log's unique ID, encoded in an opaque vector as
described in Section 4.3. described in Section 4.4.
"timestamp" is equal to the timestamp from the
"TimestampedCertificateEntryDataV2" structure encapsulated in the
"timestamped_entry".
"sct_extension_type" identifies a single extension from the IANA
registry in Section 10.6. At the time of writing, no extensions are
specified.
The interpretation of the "sct_extension_data" field is determined "timestamp" is equal to the timestamp from the corresponding
solely by the value of the "sct_extension_type" field. Each document "TimestampedCertificateEntryDataV2" structure.
that registers a new "sct_extension_type" must describe how to
interpret the corresponding "sct_extension_data".
"sct_extensions" is a vector of 0 or more SCT extensions. This "sct_extensions" is a vector of 0 or more SCT extensions. This
vector MUST NOT include more than one extension with the same vector MUST NOT include more than one extension with the same
"sct_extension_type". The extensions in the vector MUST be ordered "extension_type". The extensions in the vector MUST be ordered by
by the value of the "sct_extension_type" field, smallest value first. the value of the "extension_type" field, smallest value first. If an
If an implementation sees an extension that it does not understand, implementation sees an extension that it does not understand, it
it SHOULD ignore that extension. Furthermore, an implementation MAY SHOULD ignore that extension. Furthermore, an implementation MAY
choose to ignore any extension(s) that it does understand. choose to ignore any extension(s) that it does understand.
The encoding of the digitally-signed element is defined in [RFC5246]. "signature" is computed over a "TransItem" structure of type
"x509_entry_v2" or "precert_entry_v2" (see Section 4.7) using the
"timestamped_entry" is a "TransItem" structure that MUST be of type signature algorithm declared in the log's parameters (see
"x509_entry_v2" or "precert_entry_v2" (see Section 4.5). Section 4.1).
4.7. Merkle Tree Head 4.9. Merkle Tree Head
The log stores information about its Merkle Tree in a The log stores information about its Merkle Tree in a
"TreeHeadDataV2": "TreeHeadDataV2":
opaque NodeHash<32..2^8-1>; opaque NodeHash<32..2^8-1>;
enum {
reserved(65535)
} SthExtensionType;
struct {
SthExtensionType sth_extension_type;
opaque sth_extension_data<0..2^16-1>;
} SthExtension;
struct { struct {
uint64 timestamp; uint64 timestamp;
uint64 tree_size; uint64 tree_size;
NodeHash root_hash; NodeHash root_hash;
SthExtension sth_extensions<0..2^16-1>; Extension sth_extensions<0..2^16-1>;
} TreeHeadDataV2; } TreeHeadDataV2;
The length of NodeHash MUST match HASH_SIZE of the log. The length of NodeHash MUST match HASH_SIZE of the log.
"sth_extension_type" identifies a single extension from the IANA
registry in Section 10.7. At the time of writing, no extensions are
specified.
The interpretation of the "sth_extension_data" field is determined
solely by the value of the "sth_extension_type" field. Each document
that registers a new "sth_extension_type" must describe how to
interpret the corresponding "sth_extension_data".
"timestamp" is the current NTP Time [RFC5905], measured in "timestamp" is the current NTP Time [RFC5905], measured in
milliseconds since the epoch (January 1, 1970, 00:00 UTC), ignoring milliseconds since the epoch (January 1, 1970, 00:00 UTC), ignoring
leap seconds. leap seconds.
"tree_size" is the number of entries currently in the log's Merkle "tree_size" is the number of entries currently in the log's Merkle
Tree. Tree.
"root_hash" is the root of the Merkle Hash Tree. "root_hash" is the root of the Merkle Hash Tree.
"sth_extensions" is a vector of 0 or more STH extensions. This "sth_extensions" is a vector of 0 or more STH extensions. This
vector MUST NOT include more than one extension with the same vector MUST NOT include more than one extension with the same
"sth_extension_type". The extensions in the vector MUST be ordered "extension_type". The extensions in the vector MUST be ordered by
by the value of the "sth_extension_type" field, smallest value first. the value of the "extension_type" field, smallest value first. If an
If an implementation sees an extension that it does not understand, implementation sees an extension that it does not understand, it
it SHOULD ignore that extension. Furthermore, an implementation MAY SHOULD ignore that extension. Furthermore, an implementation MAY
choose to ignore any extension(s) that it does understand. choose to ignore any extension(s) that it does understand.
4.8. Signed Tree Head (STH) 4.10. Signed Tree Head (STH)
Periodically each log SHOULD sign its current tree head information Periodically each log SHOULD sign its current tree head information
(see Section 4.7) to produce an STH. When a client requests a log's (see Section 4.9) to produce an STH. When a client requests a log's
latest STH (see Section 5.3), the log MUST return an STH that is no latest STH (see Section 5.2), the log MUST return an STH that is no
older than the log's MMD. However, STHs could be used to mark older than the log's MMD. However, since STHs could be used to mark
individual clients (by producing a new one for each query), so logs individual clients (by producing a new STH for each query), a log
MUST NOT produce them more frequently than is declared in their MUST NOT produce STHs more frequently than its parameters declare
metadata. In general, there is no need to produce a new STH unless (see Section 4.1). In general, there is no need to produce a new STH
there are new entries in the log; however, in the unlikely event that unless there are new entries in the log; however, in the event that a
it receives no new submissions during an MMD period, the log SHALL log does not accept any submissions during an MMD period, the log
sign the same Merkle Tree Hash with a fresh timestamp. MUST sign the same Merkle Tree Hash with a fresh timestamp.
An STH is a "TransItem" structure of type "signed_tree_head_v2", An STH is a "TransItem" structure of type "signed_tree_head_v2",
which encapsulates a "SignedTreeHeadDataV2" structure: which encapsulates a "SignedTreeHeadDataV2" structure:
struct { struct {
LogID log_id; LogID log_id;
TreeHeadDataV2 tree_head; TreeHeadDataV2 tree_head;
digitally-signed struct { opaque signature<0..2^16-1>;
TreeHeadDataV2 tree_head;
} signature;
} SignedTreeHeadDataV2; } SignedTreeHeadDataV2;
"log_id" is this log's unique ID, encoded in an opaque vector as "log_id" is this log's unique ID, encoded in an opaque vector as
described in Section 4.3. described in Section 4.4.
The "timestamp" in "tree_head" MUST be at least as recent as the most The "timestamp" in "tree_head" MUST be at least as recent as the most
recent SCT timestamp in the tree. Each subsequent timestamp MUST be recent SCT timestamp in the tree. Each subsequent timestamp MUST be
more recent than the timestamp of the previous update. more recent than the timestamp of the previous update.
"tree_head" contains the latest tree head information (see "tree_head" contains the latest tree head information (see
Section 4.7). Section 4.9).
"signature" is a signature over the encoded "tree_head" field. "signature" is computed over the "tree_head" field using the
signature algorithm declared in the log's parameters (see
Section 4.1).
4.9. Merkle Consistency Proofs 4.11. Merkle Consistency Proofs
To prepare a Merkle Consistency Proof for distribution to clients, To prepare a Merkle Consistency Proof for distribution to clients,
the log produces a "TransItem" structure of type the log produces a "TransItem" structure of type
"consistency_proof_v2", which encapsulates a "ConsistencyProofDataV2" "consistency_proof_v2", which encapsulates a "ConsistencyProofDataV2"
structure: structure:
struct { struct {
LogID log_id; LogID log_id;
uint64 tree_size_1; uint64 tree_size_1;
uint64 tree_size_2; uint64 tree_size_2;
NodeHash consistency_path<1..2^16-1>; NodeHash consistency_path<1..2^16-1>;
} ConsistencyProofDataV2; } ConsistencyProofDataV2;
"log_id" is this log's unique ID, encoded in an opaque vector as "log_id" is this log's unique ID, encoded in an opaque vector as
described in Section 4.3. described in Section 4.4.
"tree_size_1" is the size of the older tree. "tree_size_1" is the size of the older tree.
"tree_size_2" is the size of the newer tree. "tree_size_2" is the size of the newer tree.
"consistency_path" is a vector of Merkle Tree nodes proving the "consistency_path" is a vector of Merkle Tree nodes proving the
consistency of two STHs. consistency of two STHs.
4.10. Merkle Inclusion Proofs 4.12. Merkle Inclusion Proofs
To prepare a Merkle Inclusion Proof for distribution to clients, the To prepare a Merkle Inclusion Proof for distribution to clients, the
log produces a "TransItem" structure of type "inclusion_proof_v2", log produces a "TransItem" structure of type "inclusion_proof_v2",
which encapsulates an "InclusionProofDataV2" structure: which encapsulates an "InclusionProofDataV2" structure:
struct { struct {
LogID log_id; LogID log_id;
uint64 tree_size; uint64 tree_size;
uint64 leaf_index; uint64 leaf_index;
NodeHash inclusion_path<1..2^16-1>; NodeHash inclusion_path<1..2^16-1>;
} InclusionProofDataV2; } InclusionProofDataV2;
"log_id" is this log's unique ID, encoded in an opaque vector as "log_id" is this log's unique ID, encoded in an opaque vector as
described in Section 4.3. described in Section 4.4.
"tree_size" is the size of the tree on which this inclusion proof is "tree_size" is the size of the tree on which this inclusion proof is
based. based.
"leaf_index" is the 0-based index of the log entry corresponding to "leaf_index" is the 0-based index of the log entry corresponding to
this inclusion proof. this inclusion proof.
"inclusion_path" is a vector of Merkle Tree nodes proving the "inclusion_path" is a vector of Merkle Tree nodes proving the
inclusion of the chosen certificate or precertificate. inclusion of the chosen certificate or precertificate.
4.11. Shutting down a log 4.13. Shutting down a log
Log operators may decide to shut down a log for various reasons, such Log operators may decide to shut down a log for various reasons, such
as deprecation of the signature algorithm. If there are entries in as deprecation of the signature algorithm. If there are entries in
the log for certificates that have not yet expired, simply making TLS the log for certificates that have not yet expired, simply making TLS
clients stop recognizing that log will have the effect of clients stop recognizing that log will have the effect of
invalidating SCTs from that log. To avoid that, the following invalidating SCTs from that log. To avoid that, the following
actions are suggested: actions are suggested:
o Make it known to clients and monitors that the log will be frozen. o Make it known to clients and monitors that the log will be frozen.
o Stop accepting new submissions (the error code "shutdown" should o Stop accepting new submissions (the error code "shutdown" should
be returned for such requests). be returned for such requests).
o Once MMD from the last accepted submission has passed and all o Once MMD from the last accepted submission has passed and all
pending submissions are incorporated, issue a final STH and pending submissions are incorporated, issue a final STH and
publish it as a part of the log's metadata. Having an STH with a publish it as one of the log's parameters. Having an STH with a
timestamp that is after the MMD has passed from the last SCT timestamp that is after the MMD has passed from the last SCT
issuance allows clients to audit this log regularly without issuance allows clients to audit this log regularly without
special handling for the final STH. At this point the log's special handling for the final STH. At this point the log's
private key is no longer needed and can be destroyed. private key is no longer needed and can be destroyed.
o Keep the log running until the certificates in all of its entries o Keep the log running until the certificates in all of its entries
have expired or exist in other logs (this can be determined by have expired or exist in other logs (this can be determined by
scanning other logs or connecting to domains mentioned in the scanning other logs or connecting to domains mentioned in the
certificates and inspecting the SCTs served). certificates and inspecting the SCTs served).
5. Log Client Messages 5. Log Client Messages
Messages are sent as HTTPS GET or POST requests. Parameters for Messages are sent as HTTPS GET or POST requests. Parameters for
POSTs and all responses are encoded as JavaScript Object Notation POSTs and all responses are encoded as JavaScript Object Notation
(JSON) objects [RFC7159]. Parameters for GETs are encoded as order- (JSON) objects [RFC7159]. Parameters for GETs are encoded as order-
independent key/value URL parameters, using the "application/x-www- independent key/value URL parameters, using the "application/x-www-
form-urlencoded" format described in the "HTML 4.01 Specification" form-urlencoded" format described in the "HTML 4.01 Specification"
[HTML401]. Binary data is base64 encoded [RFC4648] as specified in [HTML401]. Binary data is base64 encoded [RFC4648] as specified in
the individual messages. the individual messages.
Clients are configured with a base URL for a log and construct URLs
for requests by appending suffixes to this base URL. This structure
places some degree of restriction on how log operators can deploy
these services, as noted in [RFC7320]. However, operational
experience with version 1 of this protocol has not indicated that
these restrictions are a problem in practice.
Note that JSON objects and URL parameters may contain fields not Note that JSON objects and URL parameters may contain fields not
specified here. These extra fields should be ignored. specified here. These extra fields should be ignored.
The <log server> prefix, which is part of the log's metadata, MAY The <log server> prefix, which is one of the log's parameters, MAY
include a path as well as a server name and a port. include a path as well as a server name and a port.
In practice, log servers may include multiple front-end machines. In practice, log servers may include multiple front-end machines.
Since it is impractical to keep these machines in perfect sync, Since it is impractical to keep these machines in perfect sync,
errors may occur that are caused by skew between the machines. Where errors may occur that are caused by skew between the machines. Where
such errors are possible, the front-end will return additional such errors are possible, the front-end will return additional
information (as specified below) making it possible for clients to information (as specified below) making it possible for clients to
make progress, if progress is possible. Front-ends MUST only serve make progress, if progress is possible. Front-ends MUST only serve
data that is free of gaps (that is, for example, no front-end will data that is free of gaps (that is, for example, no front-end will
respond with an STH unless it is also able to prove consistency from respond with an STH unless it is also able to prove consistency from
skipping to change at page 23, line 25 skipping to change at page 26, line 16
HTTP response code of 4xx/5xx (see [RFC7231]), and, in place of the HTTP response code of 4xx/5xx (see [RFC7231]), and, in place of the
responses outlined in the subsections below, the body SHOULD be a responses outlined in the subsections below, the body SHOULD be a
JSON structure containing at least the following field: JSON structure containing at least the following field:
error_message: A human-readable string describing the error which error_message: A human-readable string describing the error which
prevented the log from processing the request. prevented the log from processing the request.
In the case of a malformed request, the string SHOULD provide In the case of a malformed request, the string SHOULD provide
sufficient detail for the error to be rectified. sufficient detail for the error to be rectified.
error_code: An error code readable by the client. Some codes are error_code: An error code readable by the client. Other than the
generic and are detailed here. Others are detailed in the generic codes detailed here, each error code is specific to the
individual requests. Error codes are fixed text strings. type of request. Specific errors are specified in the respective
sections below. Error codes are fixed text strings.
+---------------+---------------------------------------------+ +---------------+---------------------------------------------+
| Error Code | Meaning | | Error Code | Meaning |
+---------------+---------------------------------------------+ +---------------+---------------------------------------------+
| not compliant | The request is not compliant with this RFC. | | not compliant | The request is not compliant with this RFC. |
+---------------+---------------------------------------------+ +---------------+---------------------------------------------+
e.g., In response to a request of "/ct/v2/get- e.g., In response to a request of "/ct/v2/get-
entries?start=100&end=99", the log would return a "400 Bad Request" entries?start=100&end=99", the log would return a "400 Bad Request"
response code with a body similar to the following: response code with a body similar to the following:
skipping to change at page 24, line 5 skipping to change at page 26, line 43
"error_code": "not compliant", "error_code": "not compliant",
} }
Clients SHOULD treat "500 Internal Server Error" and "503 Service Clients SHOULD treat "500 Internal Server Error" and "503 Service
Unavailable" responses as transient failures and MAY retry the same Unavailable" responses as transient failures and MAY retry the same
request without modification at a later date. Note that as per request without modification at a later date. Note that as per
[RFC7231], in the case of a 503 response the log MAY include a [RFC7231], in the case of a 503 response the log MAY include a
"Retry-After:" header in order to request a minimum time for the "Retry-After:" header in order to request a minimum time for the
client to wait before retrying the request. client to wait before retrying the request.
5.1. Add Chain to Log 5.1. Submit Entry to Log
POST https://<log server>/ct/v2/add-chain POST https://<log server>/ct/v2/submit-entry
Inputs: Inputs:
chain: An array of base64 encoded certificates. The first submission: The base64 encoded certificate or precertificate.
element is the certificate for which the submitter desires an
SCT; the second certifies the first and so on to the last, type: The "VersionedTransType" integer value that indicates the
which either is, or is certified by, an accepted trust anchor. type of the "submission": 1 for "x509_entry_v2", or 2 for
"precert_entry_v2".
chain: An array of zero or more base64 encoded CA certificates.
The first element is the signer of the "submission"; the second
certifies the first; etc. The last element of "chain" (or, if
"chain" is an empty array, the "submission") either is, or is
certified by, an accepted trust anchor.
Outputs: Outputs:
sct: A base64 encoded "TransItem" of type "x509_sct_v2", signed sct: A base64 encoded "TransItem" of type "x509_sct_v2" or
by this log, that corresponds to the submitted certificate. "precert_sct_v2", signed by this log, that corresponds to the
"submission".
If the submitted entry is immediately appended to (or already
exists in) this log's tree, then the log SHOULD also output:
sth: A base64 encoded "TransItem" of type "signed_tree_head_v2",
signed by this log.
inclusion: A base64 encoded "TransItem" of type
"inclusion_proof_v2" whose "inclusion_path" array of Merkle
Tree nodes proves the inclusion of the "submission" in the
returned "sth".
Error codes: Error codes:
+-------------+-----------------------------------------------------+ +-------------+-----------------------------------------------------+
| Error Code | Meaning | | Error Code | Meaning |
+-------------+-----------------------------------------------------+ +-------------+-----------------------------------------------------+
| unknown | The last certificate in the chain both is not, and | | bad | "submission" is neither a valid certificate nor a |
| anchor | is not certified by, an accepted trust anchor. | | submission | valid precertificate. |
| | | | | |
| bad chain | The alleged chain is not actually a chain of | | bad type | "type" is neither 1 nor 2. |
| | certificates. |
| | | | | |
| bad | One or more certificates in the chain are not valid | | bad chain | The first element of "chain" is not the signer of |
| certificate | (e.g., not properly encoded). | | | the "submission", or the second element does not |
| | certify the first, etc. |
| | | | | |
| shutdown | The log has ceased operation and is not accepting | | bad | One or more certificates in the "chain" are not |
| | new submissions. | | certificate | valid (e.g., not properly encoded). |
| | |
| unknown | The last element of "chain" (or, if "chain" is an |
| anchor | empty array, the "submission") both is not, and is |
| | not certified by, an accepted trust anchor. |
| | |
| shutdown | The log is no longer accepting submissions. |
+-------------+-----------------------------------------------------+ +-------------+-----------------------------------------------------+
If the version of "sct" is not v2, then a v2 client may be unable to If the version of "sct" is not v2, then a v2 client may be unable to
verify the signature. It MUST NOT construe this as an error. This verify the signature. It MUST NOT construe this as an error. This
is to avoid forcing an upgrade of compliant v2 clients that do not is to avoid forcing an upgrade of compliant v2 clients that do not
use the returned SCTs. use the returned SCTs.
If a log detects bad encoding in a chain that otherwise verifies If a log detects bad encoding in a chain that otherwise verifies
correctly then the log MUST either log the certificate or return the correctly then the log MUST either log the certificate or return the
"bad certificate" error. If the certificate is logged, an SCT MUST "bad certificate" error. If the certificate is logged, an SCT MUST
be issued. Logging the certificate is useful, because monitors be issued. Logging the certificate is useful, because monitors
(Section 8.3) can then detect these encoding errors, which may be (Section 8.2) can then detect these encoding errors, which may be
accepted by some TLS clients. accepted by some TLS clients.
5.2. Add PreCertChain to Log If the returned "sct" is intended to be provided to clients, then
"sth" and "inclusion" (if returned) SHOULD also be provided to
POST https://<log server>/ct/v2/add-pre-chain clients (e.g., if "type" was 1 then all three "TransItem"s could be
embedded in the certificate).
Inputs:
precertificate: The base64 encoded precertificate.
chain: An array of base64 encoded CA certificates. The first
element is the signer of the precertificate; the second
certifies the first and so on to the last, which either is, or
is certified by, an accepted trust anchor.
Outputs:
sct: A base64 encoded "TransItem" of type "precert_sct_v2",
signed by this log, that corresponds to the submitted
precertificate.
Errors are the same as in Section 5.1.
5.3. Retrieve Latest Signed Tree Head 5.2. Retrieve Latest Signed Tree Head
GET https://<log server>/ct/v2/get-sth GET https://<log server>/ct/v2/get-sth
No inputs. No inputs.
Outputs: Outputs:
sth: A base64 encoded "TransItem" of type "signed_tree_head_v2", sth: A base64 encoded "TransItem" of type "signed_tree_head_v2",
signed by this log, that is no older than the log's MMD. signed by this log, that is no older than the log's MMD.
5.4. Retrieve Merkle Consistency Proof between Two Signed Tree Heads 5.3. Retrieve Merkle Consistency Proof between Two Signed Tree Heads
GET https://<log server>/ct/v2/get-sth-consistency GET https://<log server>/ct/v2/get-sth-consistency
Inputs: Inputs:
first: The tree_size of the older tree, in decimal. first: The tree_size of the older tree, in decimal.
second: The tree_size of the newer tree, in decimal (optional). second: The tree_size of the newer tree, in decimal (optional).
Both tree sizes must be from existing v2 STHs. However, because Both tree sizes must be from existing v2 STHs. However, because
skipping to change at page 26, line 12 skipping to change at page 29, line 32
(or has been omitted), then the latest known STH is returned, (or has been omitted), then the latest known STH is returned,
along with a consistency proof between the first STH and the along with a consistency proof between the first STH and the
latest. If neither are known, then the latest known STH is latest. If neither are known, then the latest known STH is
returned without a consistency proof. returned without a consistency proof.
Outputs: Outputs:
consistency: A base64 encoded "TransItem" of type consistency: A base64 encoded "TransItem" of type
"consistency_proof_v2", whose "tree_size_1" MUST match the "consistency_proof_v2", whose "tree_size_1" MUST match the
"first" input. If the "sth" output is omitted, then "first" input. If the "sth" output is omitted, then
"tree_size_2" MUST match the "second" input. "tree_size_2" MUST match the "second" input. If "first" and
"second" are equal and correspond to a known STH, the returned
consistency proof MUST be empty (a "consistency_path" array
with zero elements).
sth: A base64 encoded "TransItem" of type "signed_tree_head_v2", sth: A base64 encoded "TransItem" of type "signed_tree_head_v2",
signed by this log. signed by this log.
Note that no signature is required for the "consistency" output as Note that no signature is required for the "consistency" output as
it is used to verify the consistency between two STHs, which are it is used to verify the consistency between two STHs, which are
signed. signed.
Error codes: Error codes:
+-------------+-----------------------------------------------------+ +-------------+-----------------------------------------------------+
| Error Code | Meaning | | Error Code | Meaning |
+-------------+-----------------------------------------------------+ +-------------+-----------------------------------------------------+
| first | "first" is before the latest known STH but is not | | first | "first" is before the latest known STH but is not |
| unknown | from an existing STH. | | unknown | from an existing STH. |
| | | | | |
| second | "second" is before the latest known STH but is not | | second | "second" is before the latest known STH but is not |
| unknown | from an existing STH. | | unknown | from an existing STH. |
+-------------+-----------------------------------------------------+ +-------------+-----------------------------------------------------+
See Section 8.4.2 for an outline of how to use the "consistency" See Section 2.1.4.2 for an outline of how to use the "consistency"
output. output.
5.5. Retrieve Merkle Inclusion Proof from Log by Leaf Hash 5.4. Retrieve Merkle Inclusion Proof from Log by Leaf Hash
GET https://<log server>/ct/v2/get-proof-by-hash GET https://<log server>/ct/v2/get-proof-by-hash
Inputs: Inputs:
hash: A base64 encoded v2 leaf hash. hash: A base64 encoded v2 leaf hash.
tree_size: The tree_size of the tree on which to base the proof, tree_size: The tree_size of the tree on which to base the proof,
in decimal. in decimal.
The "hash" must be calculated as defined in Section 4.5. The The "hash" must be calculated as defined in Section 4.7. The
"tree_size" must designate an existing v2 STH. Because of skew, "tree_size" must designate an existing v2 STH. Because of skew,
the front-end may not know the requested STH. In that case, it the front-end may not know the requested STH. In that case, it
will return the latest STH it knows, along with an inclusion proof will return the latest STH it knows, along with an inclusion proof
to that STH. If the front-end knows the requested STH then only to that STH. If the front-end knows the requested STH then only
"inclusion" is returned. "inclusion" is returned.
Outputs: Outputs:
inclusion: A base64 encoded "TransItem" of type inclusion: A base64 encoded "TransItem" of type
"inclusion_proof_v2" whose "inclusion_path" array of Merkle "inclusion_proof_v2" whose "inclusion_path" array of Merkle
skipping to change at page 27, line 34 skipping to change at page 31, line 16
| Error | Meaning | | Error | Meaning |
| Code | | | Code | |
+-----------+-------------------------------------------------------+ +-----------+-------------------------------------------------------+
| hash | "hash" is not the hash of a known leaf (may be caused | | hash | "hash" is not the hash of a known leaf (may be caused |
| unknown | by skew or by a known certificate not yet merged). | | unknown | by skew or by a known certificate not yet merged). |
| | | | | |
| tree_size | "hash" is before the latest known STH but is not from | | tree_size | "hash" is before the latest known STH but is not from |
| unknown | an existing STH. | | unknown | an existing STH. |
+-----------+-------------------------------------------------------+ +-----------+-------------------------------------------------------+
See Section 8.4.1 for an outline of how to use the "inclusion" See Section 2.1.3.2 for an outline of how to use the "inclusion"
output. output.
5.6. Retrieve Merkle Inclusion Proof, Signed Tree Head and Consistency 5.5. Retrieve Merkle Inclusion Proof, Signed Tree Head and Consistency
Proof by Leaf Hash Proof by Leaf Hash
GET https://<log server>/ct/v2/get-all-by-hash GET https://<log server>/ct/v2/get-all-by-hash
Inputs: Inputs:
hash: A base64 encoded v2 leaf hash. hash: A base64 encoded v2 leaf hash.
tree_size: The tree_size of the tree on which to base the proofs, tree_size: The tree_size of the tree on which to base the proofs,
in decimal. in decimal.
The "hash" must be calculated as defined in Section 4.5. The The "hash" must be calculated as defined in Section 4.7. The
"tree_size" must designate an existing v2 STH. "tree_size" must designate an existing v2 STH.
Because of skew, the front-end may not know the requested STH or Because of skew, the front-end may not know the requested STH or
the requested hash, which leads to a number of cases. the requested hash, which leads to a number of cases.
latest STH < requested STH Return latest STH. latest STH < requested STH Return latest STH.
latest STH > requested STH Return latest STH and a consistency latest STH > requested STH Return latest STH and a consistency
proof between it and the requested STH (see Section 5.4). proof between it and the requested STH (see Section 5.3).
index of requested hash < latest STH Return "inclusion". index of requested hash < latest STH Return "inclusion".
Note that more than one case can be true, in which case the Note that more than one case can be true, in which case the
returned data is their concatenation. It is also possible for returned data is their concatenation. It is also possible for
none to be true, in which case the front-end MUST return an empty none to be true, in which case the front-end MUST return an empty
response. response.
Outputs: Outputs:
skipping to change at page 28, line 38 skipping to change at page 32, line 25
signed by this log. signed by this log.
consistency: A base64 encoded "TransItem" of type consistency: A base64 encoded "TransItem" of type
"consistency_proof_v2" that proves the consistency of the "consistency_proof_v2" that proves the consistency of the
requested STH and the returned STH. requested STH and the returned STH.
Note that no signature is required for the "inclusion" or Note that no signature is required for the "inclusion" or
"consistency" outputs as they are used to verify inclusion in and "consistency" outputs as they are used to verify inclusion in and
consistency of STHs, which are signed. consistency of STHs, which are signed.
Errors are the same as in Section 5.5. Errors are the same as in Section 5.4.
See Section 8.4.1 for an outline of how to use the "inclusion" See Section 2.1.3.2 for an outline of how to use the "inclusion"
output, and see Section 8.4.2 for an outline of how to use the output, and see Section 2.1.4.2 for an outline of how to use the
"consistency" output. "consistency" output.
5.7. Retrieve Entries and STH from Log 5.6. Retrieve Entries and STH from Log
GET https://<log server>/ct/v2/get-entries GET https://<log server>/ct/v2/get-entries
Inputs: Inputs:
start: 0-based index of first entry to retrieve, in decimal. start: 0-based index of first entry to retrieve, in decimal.
end: 0-based index of last entry to retrieve, in decimal. end: 0-based index of last entry to retrieve, in decimal.
Outputs: Outputs:
entries: An array of objects, each consisting of entries: An array of objects, each consisting of
leaf_input: The base64 encoded "TransItem" structure of type log_entry: The base64 encoded "TransItem" structure of type
"x509_entry_v2" or "precert_entry_v2" (see Section 4.5). "x509_entry_v2" or "precert_entry_v2" (see Section 4.3).
log_entry: The base64 encoded log entry (see Section 4.2). In submitted_entry: JSON object representing the inputs that were
the case of an "x509_entry_v2" entry, this is the whole submitted to "submit-entry", with the addition of the trust
"X509ChainEntry"; and in the case of a "precert_entry_v2", anchor to the "chain" field if the submission did not
this is the whole "PrecertChainEntryV2". include it.
sct: The base64 encoded "TransItem" of type "x509_sct_v2" or sct: The base64 encoded "TransItem" of type "x509_sct_v2" or
"precert_sct_v2" corresponding to this log entry. "precert_sct_v2" corresponding to this log entry.
sth: A base64 encoded "TransItem" of type "signed_tree_head_v2", sth: A base64 encoded "TransItem" of type "signed_tree_head_v2",
signed by this log. signed by this log.
Note that this message is not signed -- the "entries" data can be Note that this message is not signed -- the "entries" data can be
verified by constructing the Merkle Tree Hash corresponding to a verified by constructing the Merkle Tree Hash corresponding to a
retrieved STH. All leaves MUST be v2. However, a compliant v2 retrieved STH. All leaves MUST be v2. However, a compliant v2
client MUST NOT construe an unrecognized TransItem type as an error. client MUST NOT construe an unrecognized TransItem type as an error.
This means it may be unable to parse some entries, but note that each This means it may be unable to parse some entries, but note that each
client can inspect the entries it does recognize as well as verify client can inspect the entries it does recognize as well as verify
the integrity of the data by treating unrecognized leaves as opaque the integrity of the data by treating unrecognized leaves as opaque
input to the tree. input to the tree.
The "start" and "end" parameters SHOULD be within the range 0 <= x < The "start" and "end" parameters SHOULD be within the range 0 <= x <
"tree_size" as returned by "get-sth" in Section 5.3. "tree_size" as returned by "get-sth" in Section 5.2.
The "start" parameter MUST be less than or equal to the "end" The "start" parameter MUST be less than or equal to the "end"
parameter. parameter.
The "chain" field in the "submission" output parameter MUST include
the trust anchor that the log used to verify the submission, even if
it was omitted in the original submission.
Log servers MUST honor requests where 0 <= "start" < "tree_size" and Log servers MUST honor requests where 0 <= "start" < "tree_size" and
"end" >= "tree_size" by returning a partial response covering only "end" >= "tree_size" by returning a partial response covering only
the valid entries in the specified range. "end" >= "tree_size" could the valid entries in the specified range. "end" >= "tree_size" could
be caused by skew. Note that the following restriction may also be caused by skew. Note that the following restriction may also
apply: apply:
Logs MAY restrict the number of entries that can be retrieved per Logs MAY restrict the number of entries that can be retrieved per
"get-entries" request. If a client requests more than the permitted "get-entries" request. If a client requests more than the permitted
number of entries, the log SHALL return the maximum number of entries number of entries, the log SHALL return the maximum number of entries
permissible. These entries SHALL be sequential beginning with the permissible. These entries SHALL be sequential beginning with the
entry specified by "start". entry specified by "start".
Because of skew, it is possible the log server will not have any Because of skew, it is possible the log server will not have any
entries between "start" and "end". In this case it MUST return an entries between "start" and "end". In this case it MUST return an
empty "entries" array. empty "entries" array.
In any case, the log server MUST return the latest STH it knows In any case, the log server MUST return the latest STH it knows
about. about.
See Section 8.4.3 for an outline of how to use a complete list of See Section 2.1.2 for an outline of how to use a complete list of
"leaf_input" entries to verify the "root_hash". "log_entry" entries to verify the "root_hash".
5.8. Retrieve Accepted Trust Anchors 5.7. Retrieve Accepted Trust Anchors
GET https://<log server>/ct/v2/get-anchors GET https://<log server>/ct/v2/get-anchors
No inputs. No inputs.
Outputs: Outputs:
certificates: An array of base64 encoded trust anchors that are certificates: An array of base64 encoded trust anchors that are
acceptable to the log. acceptable to the log.
max_chain: If the server has chosen to limit the length of chains max_chain_length: If the server has chosen to limit the length of
it accepts, this is the maximum number of certificates in the chains it accepts, this is the maximum number of certificates
chain, in decimal. If there is no limit, this is omitted. in the chain, in decimal. If there is no limit, this is
omitted.
6. TLS Servers 6. TLS Servers
TLS servers MUST use at least one of the three mechanisms listed TLS servers MUST use at least one of the three mechanisms listed
below to present one or more SCTs from one or more logs to each TLS below to present one or more SCTs from one or more logs to each TLS
client during full TLS handshakes, where each SCT corresponds to the client during full TLS handshakes, where each SCT corresponds to the
server certificate. TLS servers SHOULD also present corresponding server certificate. TLS servers SHOULD also present corresponding
inclusion proofs and STHs (see Section 6.3). inclusion proofs and STHs.
Three mechanisms are provided because they have different tradeoffs. Three mechanisms are provided because they have different tradeoffs.
o A TLS extension (Section 7.4.1.4 of [RFC5246]) with type o A TLS extension (Section 7.4.1.4 of [RFC5246]) with type
"transparency_info" (see Section 6.5). This mechanism allows TLS "transparency_info" (see Section 6.4). This mechanism allows TLS
servers to participate in CT without the cooperation of CAs, servers to participate in CT without the cooperation of CAs,
unlike the other two mechanisms. It also allows SCTs and unlike the other two mechanisms. It also allows SCTs and
inclusion proofs to be updated on the fly. inclusion proofs to be updated on the fly.
o An Online Certificate Status Protocol (OCSP) [RFC6960] response o An Online Certificate Status Protocol (OCSP) [RFC6960] response
extension (see Section 7.1.1), where the OCSP response is provided extension (see Section 7.1.1), where the OCSP response is provided
in the "CertificateStatus" message, provided that the TLS client in the "CertificateStatus" message, provided that the TLS client
included the "status_request" extension in the (extended) included the "status_request" extension in the (extended)
"ClientHello" (Section 8 of [RFC6066]). This mechanism, popularly "ClientHello" (Section 8 of [RFC6066]). This mechanism, popularly
known as OCSP stapling, is already widely (but not universally) known as OCSP stapling, is already widely (but not universally)
skipping to change at page 32, line 27 skipping to change at page 36, line 12
SerializedTransItem trans_item_list<1..2^16-1>; SerializedTransItem trans_item_list<1..2^16-1>;
} TransItemList; } TransItemList;
Here, "SerializedTransItem" is an opaque byte string that contains Here, "SerializedTransItem" is an opaque byte string that contains
the serialized "TransItem" structure. This encoding ensures that TLS the serialized "TransItem" structure. This encoding ensures that TLS
clients can decode each "TransItem" individually (so, for example, if clients can decode each "TransItem" individually (so, for example, if
there is a version upgrade, out-of-date clients can still parse old there is a version upgrade, out-of-date clients can still parse old
"TransItem" structures while skipping over new "TransItem" structures "TransItem" structures while skipping over new "TransItem" structures
whose versions they don't understand). whose versions they don't understand).
6.3. Presenting SCTs, inclusion proofs and STHs 6.3. Presenting SCTs, inclusions proofs and STHs
When constructing a "TransItemList" structure, a TLS server SHOULD
construct and include "TransItem" structures of type
"x509_sct_with_proof_v2" (for an SCT of type "x509_sct_v2") or
"precert_sct_with_proof_v2" (for an SCT of type "precert_sct_v2"),
both of which encapsulate a "SCTWithProofDataV2" structure:
struct {
SignedCertificateTimestampDataV2 sct;
SignedTreeHeadDataV2 sth;
InclusionProofDataV2 inclusion_proof;
} SCTWithProofDataV2;
"sct" is the encapsulated data structure from an SCT that corresponds
to the server certificate.
"sth" is the encapsulated data structure from an STH that was signed
by the same log as "sct".
"inclusion_proof" is the encapsulated data structure from an
inclusion proof that corresponds to "sct" and can be used to compute
the root in "sth".
6.4. Presenting SCTs only In each "TransItemList" that is sent to a client during a TLS
handshake, the TLS server MUST include a "TransItem" structure of
type "x509_sct_v2" or "precert_sct_v2" (except as described in
Section 6.5).
Presenting inclusion proofs and STHs in the TLS handshake helps to Presenting inclusion proofs and STHs in the TLS handshake helps to
protect the client's privacy (see Section 8.2.4) and reduces load on protect the client's privacy (see Section 8.1.5) and reduces load on
log servers. However, if a TLS server is unable to obtain an log servers. Therefore, if the TLS server can obtain them, it SHOULD
inclusion proof and STH that correspond to an SCT, then it MUST also include "TransItem"s of type "inclusion_proof_v2" and
include "TransItem" structures of type "x509_sct_v2" or "signed_tree_head_v2" in the "TransItemList".
"precert_sct_v2" in the "TransItemList".
6.5. transparency_info TLS Extension 6.4. transparency_info TLS Extension
Provided that a TLS client includes the "transparency_info" extension Provided that a TLS client includes the "transparency_info" extension
type in the ClientHello, the TLS server SHOULD include the type in the ClientHello, the TLS server SHOULD include the
"transparency_info" extension in the ServerHello with "transparency_info" extension in the ServerHello with
"extension_data" set to a "TransItemList". The TLS server SHOULD "extension_data" set to a "TransItemList". The TLS server SHOULD
ignore any "extension_data" sent by the TLS client. Additionally, ignore any "extension_data" sent by the TLS client. Additionally,
the TLS server MUST NOT process or include this extension when a TLS the TLS server MUST NOT process or include this extension when a TLS
session is resumed, since session resumption uses the original session is resumed, since session resumption uses the original
session information. session information.
6.6. cached_info TLS Extension 6.5. cached_info TLS Extension
When a TLS server includes the "transparency_info" extension in the When a TLS server includes the "transparency_info" extension in the
ServerHello, it SHOULD NOT include any "TransItem" structures of type ServerHello, it SHOULD NOT include any "TransItem" structures of type
"x509_sct_with_proof_v2", "x509_sct_v2", "precert_sct_with_proof_v2" "x509_sct_v2" or "precert_sct_v2" in the "TransItemList" if all of
or "precert_sct_v2" in the "TransItemList" if all of the following the following conditions are met:
conditions are met:
o The TLS client includes the "transparency_info" extension type in o The TLS client includes the "transparency_info" extension type in
the ClientHello. the ClientHello.
o The TLS client includes the "cached_info" ([RFC7924]) extension o The TLS client includes the "cached_info" ([RFC7924]) extension
type in the ClientHello, with a "CachedObject" of type type in the ClientHello, with a "CachedObject" of type
"ct_compliant" (see Section 8.2.7) and at least one "CachedObject" "ct_compliant" (see Section 8.1.7) and at least one "CachedObject"
of type "cert". of type "cert".
o The TLS server sends a modified Certificate message (as described o The TLS server sends a modified Certificate message (as described
in section 4.1 of [RFC7924]). in section 4.1 of [RFC7924]).
TLS servers SHOULD ignore the "hash_value" fields of each TLS servers SHOULD ignore the "hash_value" fields of each
"CachedObject" of type "ct_compliant" sent by TLS clients. "CachedObject" of type "ct_compliant" sent by TLS clients.
7. Certification Authorities 7. Certification Authorities
7.1. Transparency Information X.509v3 Extension 7.1. Transparency Information X.509v3 Extension
The Transparency Information X.509v3 extension, which has OID The Transparency Information X.509v3 extension, which has OID
1.3.101.75 and SHOULD be non-critical, contains one or more 1.3.101.75 and SHOULD be non-critical, contains one or more
"TransItem" structures in a "TransItemList". This extension MAY be "TransItem" structures in a "TransItemList". This extension MAY be
included in OCSP responses (see Section 7.1.1) and certificates (see included in OCSP responses (see Section 7.1.1) and certificates (see
Section 7.1.2). Since RFC5280 requires the "extnValue" field (an Section 7.1.2). Since RFC5280 requires the "extnValue" field (an
OCTET STRING) of each X.509v3 extension to include the DER encoding OCTET STRING) of each X.509v3 extension to include the DER encoding
of an ASN.1 value, a "TransItemList" MUST NOT be included directly. of an ASN.1 value, a "TransItemList" MUST NOT be included directly.
Instead, it MUST be wrapped inside an additional OCTET STRING, which Instead, it MUST be wrapped inside an additional OCTET STRING, which
skipping to change at page 34, line 24 skipping to change at page 37, line 30
is then put into the "extnValue" field: is then put into the "extnValue" field:
TransparencyInformationSyntax ::= OCTET STRING TransparencyInformationSyntax ::= OCTET STRING
"TransparencyInformationSyntax" contains a "TransItemList". "TransparencyInformationSyntax" contains a "TransItemList".
7.1.1. OCSP Response Extension 7.1.1. OCSP Response Extension
A certification authority MAY include a Transparency Information A certification authority MAY include a Transparency Information
X.509v3 extension in the "singleExtensions" of a "SingleResponse" in X.509v3 extension in the "singleExtensions" of a "SingleResponse" in
an OCSP response. The included SCTs or inclusion proofs MUST be for an OCSP response. All included SCTs and inclusion proofs MUST be for
the certificate identified by the "certID" of that "SingleResponse", the certificate identified by the "certID" of that "SingleResponse",
or for a precertificate that corresponds to that certificate. or for a precertificate that corresponds to that certificate.
7.1.2. Certificate Extension 7.1.2. Certificate Extension
A certification authority MAY include a Transparency Information A certification authority MAY include a Transparency Information
X.509v3 extension in a certificate. Any included SCTs or inclusion X.509v3 extension in a certificate. All included SCTs and inclusion
proofs MUST be for a precertificate that corresponds to this proofs MUST be for a precertificate that corresponds to this
certificate. certificate.
7.2. TLS Feature Extension 7.2. TLS Feature X.509v3 Extension
A certification authority MAY include the transparency_info A certification authority SHOULD NOT issue any certificate that
(Section 6.5) TLS extension identifier in the TLS Feature [RFC7633] identifies the "transparency_info" TLS extension in a TLS feature
certificate extension in root, intermediate and end-entity extension [RFC7633], because TLS servers are not required to support
certificates. When a certificate chain includes such a certificate, the "transparency_info" TLS extension in order to participate in CT
this indicates that CT compliance is required. (see Section 6).
8. Clients 8. Clients
There are various different functions clients of logs might perform. There are various different functions clients of logs might perform.
We describe here some typical clients and how they should function. We describe here some typical clients and how they should function.
Any inconsistency may be used as evidence that a log has not behaved Any inconsistency may be used as evidence that a log has not behaved
correctly, and the signatures on the data structures prevent the log correctly, and the signatures on the data structures prevent the log
from denying that misbehavior. from denying that misbehavior.
All clients need various metadata in order to communicate with logs All clients need various parameters in order to communicate with logs
and verify their responses. This metadata is described below, but and verify their responses. These parameters are described in
note that this document does not describe how the metadata is Section 4.1, but note that this document does not describe how the
obtained, which is implementation dependent (see, for example, parameters are obtained, which is implementation-dependent (see, for
[Chromium.Policy]). example, [Chromium.Policy]).
Clients should somehow exchange STHs they see, or make them available Clients should somehow exchange STHs they see, or make them available
for scrutiny, in order to ensure that they all have a consistent for scrutiny, in order to ensure that they all have a consistent
view. The exact mechanisms will be in separate documents, but it is view. The exact mechanisms will be in separate documents, but it is
expected there will be a variety. expected there will be a variety.
8.1. Metadata 8.1. TLS Client
In order to communicate with and verify a log, clients need metadata
about the log.
Base URL: The URL to substitute for <log server> in Section 5.
Hash Algorithm: The hash algorithm used for the Merkle Tree (see
Section 10.3).
Signing Algorithm: The signing algorithm used (see Section 2.1.4).
Public Key: The public key used to verify signatures generated by
the log. A log MUST NOT use the same keypair as any other log.
Log ID: The OID that uniquely identifies the log.
Maximum Merge Delay: The MMD the log has committed to.
Version: The version of the protocol supported by the log (currently
1 or 2).
Maximum Chain Length: The longest chain submission the log is
willing to accept, if the log chose to limit it.
STH Frequency Count: The maximum number of STHs the log may produce
in any period equal to the "Maximum Merge Delay" (see
Section 4.8).
Final STH: If a log has been closed down (i.e., no longer accepts
new entries), existing entries may still be valid. In this case,
the client should know the final valid STH in the log to ensure no
new entries can be added without detection. The final STH should
be provided in the form of a TransItem of type
"signed_tree_head_v2".
[JSON.Metadata] is an example of a metadata format which includes the
above elements.
8.2. TLS Client
8.2.1. Receiving SCTs 8.1.1. Receiving SCTs and inclusion proofs
TLS clients receive SCTs alongside or in certificates. TLS clients TLS clients receive SCTs alongside or in certificates. TLS clients
MUST implement all of the three mechanisms by which TLS servers may MUST implement all of the three mechanisms by which TLS servers may
present SCTs (see Section 6). TLS clients MAY also accept SCTs via present SCTs (see Section 6). TLS clients MAY also accept SCTs via
the "status_request_v2" extension ([RFC6961]). TLS clients that the "status_request_v2" extension ([RFC6961]). TLS clients that
support the "transparency_info" TLS extension SHOULD include it in support the "transparency_info" TLS extension SHOULD include it in
ClientHello messages, with empty "extension_data". TLS clients may ClientHello messages, with empty "extension_data". TLS clients may
also receive inclusion proofs in addition to SCTs, which should be also receive inclusion proofs in addition to SCTs, which should be
checked once the SCTs are validated. checked once the SCTs are validated.
8.2.2. Reconstructing the TBSCertificate 8.1.2. Reconstructing the TBSCertificate
To reconstruct the TBSCertificate component of a precertificate from To reconstruct the TBSCertificate component of a precertificate from
a certificate, TLS clients should remove the Transparency Information a certificate, TLS clients should remove the Transparency Information
extension described in Section 7.1. extension described in Section 7.1.
If the SCT checked is for a Precertificate (where the "type" of the If the SCT checked is for a precertificate (where the "type" of the
"TransItem" is "precert_sct_v2"), then the client SHOULD also remove "TransItem" is "precert_sct_v2"), then the client SHOULD also remove
embedded v1 SCTs, identified by OID 1.3.6.1.4.1.11129.2.4.2 (See embedded v1 SCTs, identified by OID 1.3.6.1.4.1.11129.2.4.2 (See
Section 3.3. of [RFC6962]), in the process of reconstructing the Section 3.3. of [RFC6962]), in the process of reconstructing the
TBSCertificate. That is to allow embedded v1 and v2 SCTs to co-exist TBSCertificate. That is to allow embedded v1 and v2 SCTs to co-exist
in a certificate (See Appendix A). in a certificate (See Appendix A).
8.2.3. Validating SCTs 8.1.3. Validating SCTs
In addition to normal validation of the server certificate and its In addition to normal validation of the server certificate and its
chain, TLS clients SHOULD validate each received SCT for which they chain, TLS clients SHOULD validate each received SCT for which they
have the corresponding log's metadata. To validate an SCT, a TLS have the corresponding log's parameters. To validate an SCT, a TLS
client computes the signature input from the SCT data and the server client computes the signature input by constructing a "TransItem" of
certificate, and then verifies the signature using the corresponding type "x509_entry_v2" or "precert_entry_v2", depending on the SCT's
log's public key. TLS clients MUST NOT consider valid any SCT whose "TransItem" type. The "TimestampedCertificateEntryDataV2" structure
timestamp is in the future. is constructed in the following manner:
8.2.4. Validating inclusion proofs o "timestamp" is copied from the SCT.
After validating a received SCT, a TLS client MAY request a o "tbs_certificate" is the reconstructed TBSCertificate portion of
corresponding inclusion proof (if one is not already available) and the server certificate, as described in Section 8.1.2.
then verify it. An inclusion proof can be requested directly from a
log using "get-proof-by-hash" (Section 5.5) or "get-all-by-hash"
(Section 5.6), but note that this will disclose to the log which TLS
server the client has been communicating with.
Alternatively, if the TLS client has received an inclusion proof (and o "issuer_key_hash" is computed as described in Section 4.7.
an STH) alongside the SCT, it can proceed to verifying the inclusion
proof to the provided STH. The client then has to verify consistency
between the provided STH and an STH it knows about, which is less
sensitive from a privacy perspective.
TLS clients SHOULD also verify each received inclusion proof (see o "sct_extensions" is copied from the SCT.
Section 8.4.1) for which they have the corresponding log's metadata,
to audit the log and gain confidence that the certificate is logged. The SCT's "signature" is then verified using the public key of the
corresponding log, which is identified by the "log_id". The required
signature algorithm is one of the log's parameters.
TLS clients MUST NOT consider valid any SCT whose timestamp is in the
future.
8.1.4. Fetching inclusion proofs
When a TLS client has validated a received SCT but does not yet
possess a corresponding inclusion proof, the TLS client MAY request
the inclusion proof directly from a log using "get-proof-by-hash"
(Section 5.4) or "get-all-by-hash" (Section 5.5). Note that this
will disclose to the log which TLS server the client has been
communicating with.
8.1.5. Validating inclusion proofs
When a TLS client has received, or fetched, an inclusion proof (and
an STH), it SHOULD proceed to verifying the inclusion proof to the
provided STH. The TLS client SHOULD also verify consistency between
the provided STH and an STH it knows about.
If the TLS client holds an STH that predates the SCT, it MAY, in the If the TLS client holds an STH that predates the SCT, it MAY, in the
process of auditing, request a new STH from the log (Section 5.3), process of auditing, request a new STH from the log (Section 5.2),
then verify it by requesting a consistency proof (Section 5.4). Note then verify it by requesting a consistency proof (Section 5.3). Note
that if the TLS client uses "get-all-by-hash", then it will already that if the TLS client uses "get-all-by-hash", then it will already
have the new STH. have the new STH.
8.2.5. Evaluating compliance 8.1.6. Evaluating compliance
To be considered compliant, a certificate MUST be accompanied by at It is up to a client's local policy to specify the quantity and form
least one valid SCT. A certificate not accompanied by any valid SCTs of evidence (SCTs, inclusion proofs or a combination) needed to
MUST NOT be considered compliant by TLS clients. achieve compliance and how to handle non-compliance.
A TLS client MUST NOT evaluate compliance if it did not send both the A TLS client MUST NOT evaluate compliance if it did not send both the
"transparency_info" and "status_request" TLS extensions in the "transparency_info" and "status_request" TLS extensions in the
ClientHello. ClientHello.
8.2.6. TLS Feature Extension 8.1.7. cached_info TLS Extension
If any certificate in a chain includes the transparency_info
(Section 6.5) TLS extension identifier in the TLS Feature [RFC7633]
certificate extension, then CT compliance (using any of the
mechanisms from Section 6) is required.
8.2.7. cached_info TLS Extension
If a TLS client uses the "cached_info" TLS extension ([RFC7924]) to If a TLS client uses the "cached_info" TLS extension ([RFC7924]) to
indicate 1 or more cached certificates, all of which it already indicate 1 or more cached certificates, all of which it already
considers to be CT compliant, the TLS client MAY also include a considers to be CT compliant, the TLS client MAY also include a
"CachedObject" of type "ct_compliant" in the "cached_info" extension. "CachedObject" of type "ct_compliant" in the "cached_info" extension.
The "hash_value" field MUST be 1 byte long with the value 0. The "hash_value" field MUST be 1 byte long with the value 0.
8.2.8. Handling of Non-compliance 8.2. Monitor
If a TLS server presents a certificate chain that is non-compliant,
and the use of a compliant certificate is mandated by an explicit
security policy, application protocol specification, the TLS Feature
extension or any other means, the TLS client MUST refuse the
connection.
8.3. Monitor
Monitors watch logs to check that they behave correctly, for Monitors watch logs to check that they behave correctly, for
certificates of interest, or both. For example, a monitor may be certificates of interest, or both. For example, a monitor may be
configured to report on all certificates that apply to a specific configured to report on all certificates that apply to a specific
domain name when fetching new entries for consistency validation. domain name when fetching new entries for consistency validation.
A monitor needs to, at least, inspect every new entry in each log it A monitor needs to, at least, inspect every new entry in each log it
watches. It may also want to keep copies of entire logs. In order watches. It may also want to keep copies of entire logs. In order
to do this, it should follow these steps for each log: to do this, it should follow these steps for each log:
1. Fetch the current STH (Section 5.3). 1. Fetch the current STH (Section 5.2).
2. Verify the STH signature. 2. Verify the STH signature.
3. Fetch all the entries in the tree corresponding to the STH 3. Fetch all the entries in the tree corresponding to the STH
(Section 5.7). (Section 5.6).
4. Confirm that the tree made from the fetched entries produces the 4. Confirm that the tree made from the fetched entries produces the
same hash as that in the STH. same hash as that in the STH.
5. Fetch the current STH (Section 5.3). Repeat until the STH 5. Fetch the current STH (Section 5.2). Repeat until the STH
changes. changes.
6. Verify the STH signature. 6. Verify the STH signature.
7. Fetch all the new entries in the tree corresponding to the STH 7. Fetch all the new entries in the tree corresponding to the STH
(Section 5.7). If they remain unavailable for an extended (Section 5.6). If they remain unavailable for an extended
period, then this should be viewed as misbehavior on the part of period, then this should be viewed as misbehavior on the part of
the log. the log.
8. Either: 8. Either:
1. Verify that the updated list of all entries generates a tree 1. Verify that the updated list of all entries generates a tree
with the same hash as the new STH. with the same hash as the new STH.
Or, if it is not keeping all log entries: Or, if it is not keeping all log entries:
1. Fetch a consistency proof for the new STH with the previous 1. Fetch a consistency proof for the new STH with the previous
STH (Section 5.4). STH (Section 5.3).
2. Verify the consistency proof. 2. Verify the consistency proof.
3. Verify that the new entries generate the corresponding 3. Verify that the new entries generate the corresponding
elements in the consistency proof. elements in the consistency proof.
9. Go to Step 5. 9. Go to Step 5.
8.4. Auditing 8.3. Auditing
Auditing ensures that the current published state of a log is Auditing ensures that the current published state of a log is
reachable from previously published states that are known to be good, reachable from previously published states that are known to be good,
and that the promises made by the log in the form of SCTs have been and that the promises made by the log in the form of SCTs have been
kept. Audits are performed by monitors or TLS clients. kept. Audits are performed by monitors or TLS clients.
In particular, there are four log behaviour properties that should be In particular, there are four log behavior properties that should be
checked: checked:
o The Maximum Merge Delay (MMD). o The Maximum Merge Delay (MMD).
o The STH Frequency Count. o The STH Frequency Count.
o The append-only property. o The append-only property.
o The consistency of the log view presented to all query sources. o The consistency of the log view presented to all query sources.
skipping to change at page 39, line 34 skipping to change at page 42, line 5
derived from the previous STH and the submitted entries incorporated derived from the previous STH and the submitted entries incorporated
into the log since publication of the previous STH. This can be into the log since publication of the previous STH. This can be
proven through auditing of STHs. SCTs returned to TLS clients can be proven through auditing of STHs. SCTs returned to TLS clients can be
audited by verifying against the accompanying certificate, and using audited by verifying against the accompanying certificate, and using
Merkle Inclusion Proofs, against the log's Merkle tree. Merkle Inclusion Proofs, against the log's Merkle tree.
The action taken by the auditor if an audit fails is not specified, The action taken by the auditor if an audit fails is not specified,
but note that in general if audit fails, the auditor is in possession but note that in general if audit fails, the auditor is in possession
of signed proof of the log's misbehavior. of signed proof of the log's misbehavior.
A monitor (Section 8.3) can audit by verifying the consistency of A monitor (Section 8.2) can audit by verifying the consistency of
STHs it receives, ensure that each entry can be fetched and that the STHs it receives, ensure that each entry can be fetched and that the
STH is indeed the result of making a tree from all fetched entries. STH is indeed the result of making a tree from all fetched entries.
A TLS client (Section 8.2) can audit by verifying an SCT against any A TLS client (Section 8.1) can audit by verifying an SCT against any
STH dated after the SCT timestamp + the Maximum Merge Delay by STH dated after the SCT timestamp + the Maximum Merge Delay by
requesting a Merkle inclusion proof (Section 5.5). It can also requesting a Merkle inclusion proof (Section 5.4). It can also
verify that the SCT corresponds to the server certificate it arrived verify that the SCT corresponds to the server certificate it arrived
with (i.e., the log entry is that certificate, or is a precertificate with (i.e., the log entry is that certificate, or is a precertificate
corresponding to that certificate). corresponding to that certificate).
Checking of the consistency of the log view presented to all entities Checking of the consistency of the log view presented to all entities
is more difficult to perform because it requires a way to share log is more difficult to perform because it requires a way to share log
responses among a set of CT-aware entities, and is discussed in responses among a set of CT-aware entities, and is discussed in
Section 11.3. Section 11.3.
The following algorithm outlines may be useful for clients that wish
to perform various audit operations.
8.4.1. Verifying an inclusion proof
When a client has received a "TransItem" of type "inclusion_proof_v2"
and wishes to verify inclusion of an input "hash" for an STH with a
given "tree_size" and "root_hash", the following algorithm may be
used to prove the "hash" was included in the "root_hash":
1. Compare "leaf_index" against "tree_size". If "leaf_index" is
greater than or equal to "tree_size" fail the proof verification.
2. Set "fn" to "leaf_index" and "sn" to "tree_size - 1".
3. Set "r" to "hash".
4. For each value "p" in the "inclusion_path" array:
If "sn" is 0, stop the iteration and fail the proof verification.
If "LSB(fn)" is set, or if "fn" is equal to "sn", then:
1. Set "r" to "HASH(0x01 || p || r)"
2. If "LSB(fn)" is not set, then right-shift both "fn" and "sn"
equally until either "LSB(fn)" is set or "fn" is "0".
Otherwise:
1. Set "r" to "HASH(0x01 || r || p)"
Finally, right-shift both "fn" and "sn" one time.
5. Compare "sn" to 0. Compare "r" against the "root_hash". If "sn"
is equal to 0, and "r" and the "root_hash" are equal, then the
log has proven the inclusion of "hash". Otherwise, fail the
proof verification.
8.4.2. Verifying consistency between two STHs
When a client has an STH "first_hash" for tree size "first", an STH
"second_hash" for tree size "second" where "0 < first < second", and
has received a "TransItem" of type "consistency_proof_v2" that they
wish to use to verify both hashes, the following algorithm may be
used:
1. If "first" is an exact power of 2, then prepend "first_hash" to
the "consistency_path" array.
2. Set "fn" to "first - 1" and "sn" to "second - 1".
3. If "LSB(fn)" is set, then right-shift both "fn" and "sn" equally
until "LSB(fn)" is not set.
4. Set both "fr" and "sr" to the first value in the
"consistency_path" array.
5. For each subsequent value "c" in the "consistency_path" array:
If "sn" is 0, stop the iteration and fail the proof verification.
If "LSB(fn)" is set, or if "fn" is equal to "sn", then:
1. Set "fr" to "HASH(0x01 || c || fr)"
Set "sr" to "HASH(0x01 || c || sr)"
2. If "LSB(fn)" is not set, then right-shift both "fn" and "sn"
equally until either "LSB(fn)" is set or "fn" is "0".
Otherwise:
1. Set "sr" to "HASH(0x01 || sr || c)"
Finally, right-shift both "fn" and "sn" one time.
6. After completing iterating through the "consistency_path" array
as described above, verify that the "fr" calculated is equal to
the "first_hash" supplied, that the "sr" calculated is equal to
the "second_hash" supplied and that "sn" is 0.
8.4.3. Verifying root hash given entries
When a client has a complete list of leaf input "entries" from "0" up
to "tree_size - 1" and wishes to verify this list against an STH
"root_hash" returned by the log for the same "tree_size", the
following algorithm may be used:
1. Set "stack" to an empty stack.
2. For each "i" from "0" up to "tree_size - 1":
1. Push "HASH(0x00 || entries[i])" to "stack".
2. Set "merge_count" to the lowest value ("0" included) such
that "LSB(i >> merge_count)" is not set. In other words, set
"merge_count" to the number of consecutive "1"s found
starting at the least significant bit of "i".
3. Repeat "merge_count" times:
1. Pop "right" from "stack".
2. Pop "left" from "stack".
3. Push "HASH(0x01 || left || right)" to "stack".
3. If there is more than one element in the "stack", repeat the same
merge procedure (Step 2.3 above) until only a single element
remains.
4. The remaining element in "stack" is the Merkle Tree hash for the
given "tree_size" and should be compared by equality against the
supplied "root_hash".
9. Algorithm Agility 9. Algorithm Agility
It is not possible for a log to change any of its algorithms part way It is not possible for a log to change any of its algorithms part way
through its lifetime: through its lifetime:
Signature algorithm: SCT signatures must remain valid so signature Signature algorithm: SCT signatures must remain valid so signature
algorithms can only be added, not removed. algorithms can only be added, not removed.
Hash algorithm: A log would have to support the old and new hash Hash algorithm: A log would have to support the old and new hash
algorithms to allow backwards-compatibility with clients that are algorithms to allow backwards-compatibility with clients that are
not aware of a hash algorithm change. not aware of a hash algorithm change.
Allowing multiple signature or hash algorithms for a log would Allowing multiple signature or hash algorithms for a log would
require that all data structures support it and would significantly require that all data structures support it and would significantly
complicate client implementation, which is why it is not supported by complicate client implementation, which is why it is not supported by
this document. this document.
If it should become necessary to deprecate an algorithm used by a If it should become necessary to deprecate an algorithm used by a
live log, then the log should be frozen as specified in Section 8.1 live log, then the log should be frozen as specified in Section 4.13
and a new log should be started. Certificates in the frozen log that and a new log should be started. Certificates in the frozen log that
have not yet expired and require new SCTs SHOULD be submitted to the have not yet expired and require new SCTs SHOULD be submitted to the
new log and the SCTs from that log used instead. new log and the SCTs from that log used instead.
10. IANA Considerations 10. IANA Considerations
The assignment policy criteria mentioned in this section refer to the The assignment policy criteria mentioned in this section refer to the
policies outlined in [RFC5226]. policies outlined in [RFC5226].
10.1. TLS Extension Type 10.1. TLS Extension Type
skipping to change at page 43, line 15 skipping to change at page 43, line 21
10.2. New Entry to the TLS CachedInformationType registry 10.2. New Entry to the TLS CachedInformationType registry
IANA is asked to add an entry for "ct_compliant(TBD)" to the "TLS IANA is asked to add an entry for "ct_compliant(TBD)" to the "TLS
CachedInformationType Values" registry that was defined in [RFC7924]. CachedInformationType Values" registry that was defined in [RFC7924].
10.3. Hash Algorithms 10.3. Hash Algorithms
IANA is asked to establish a registry of hash algorithm values, named IANA is asked to establish a registry of hash algorithm values, named
"CT Hash Algorithms", that initially consists of: "CT Hash Algorithms", that initially consists of:
+------------+---------------+--------------------------------------+ +--------+------------+------------------------+--------------------+
| Value | Hash | Reference / Assignment Policy | | Value | Hash | OID | Reference / |
| | Algorithm | | | | Algorithm | | Assignment Policy |
+------------+---------------+--------------------------------------+ +--------+------------+------------------------+--------------------+
| 0x00 | SHA-256 | [RFC4634] | | 0x00 | SHA-256 | 2.16.840.1.101.3.4.2.1 | [RFC6234] |
| | | | | | | | |
| 0x01 - | Unassigned | Specification Required and Expert | | 0x01 - | Unassigned | | Specification |
| 0xDF | | Review | | 0xDF | | | Required and |
| | | | | | | | Expert Review |
| 0xE0 - | Reserved | Experimental Use | | | | | |
| 0xEF | | | | 0xE0 - | Reserved | | Experimental Use |
| | | | | 0xEF | | | |
| 0xF0 - | Reserved | Private Use | | | | | |
| 0xFF | | | | 0xF0 - | Reserved | | Private Use |
+------------+---------------+--------------------------------------+ | 0xFF | | | |
+--------+------------+------------------------+--------------------+
10.3.1. Expert Review guidelines 10.3.1. Expert Review guidelines
The appointed Expert should ensure that the proposed algorithm has a The appointed Expert should ensure that the proposed algorithm has a
public specification and is suitable for use as a cryptographic hash public specification and is suitable for use as a cryptographic hash
algorithm with no known preimage or collision attacks. These attacks algorithm with no known preimage or collision attacks. These attacks
can damage the integrity of the log. can damage the integrity of the log.
10.4. Signature Algorithms 10.4. Signature Algorithms
IANA is asked to establish a registry of signature algorithm values, IANA is asked to establish a registry of signature algorithm values,
named "CT Signature Algorithms", that initially consists of: named "CT Signature Algorithms", that initially consists of:
+---------+-------------------------------+-------------------------+ +--------------------------------+--------------------+-------------+
| Value | Signature Algorithm | Reference / Assignment | | SignatureScheme Value | Signature | Reference / |
| | | Policy | | | Algorithm | Assignment |
+---------+-------------------------------+-------------------------+ | | | Policy |
| 0x00 | Deterministic ECDSA (NIST | [RFC6979] | +--------------------------------+--------------------+-------------+
| | P-256) with HMAC-SHA256 | | | ecdsa_secp256r1_sha256(0x0403) | ECDSA (NIST P-256) | [FIPS186-4] |
| | | | | | with SHA-256 | |
| 0x01 | RSA (RSASSA-PKCS1-v1_5, key | [RFC8017] | | | | |
| | >= 2048 bits) with SHA-256 | | | ecdsa_secp256r1_sha256(0x0403) | Deterministic | [RFC6979] |
| | | | | | ECDSA (NIST P-256) | |
| 0x02 - | Unassigned | Specification Required | | | with HMAC-SHA256 | |
| 0xDF | | and Expert Review | | | | |
| | | | | ed25519(0x0807) | Ed25519 (PureEdDSA | [RFC8032] |
| 0xE0 - | Reserved | Experimental Use | | | with the | |
| 0xEF | | | | | edwards25519 | |
| | | | | | curve) | |
| 0xF0 - | Reserved | Private Use | | | | |
| 0xFF | | | | private_use(0xFE00..0xFFFF) | Reserved | Private Use |
+---------+-------------------------------+-------------------------+ +--------------------------------+--------------------+-------------+
10.4.1. Expert Review guidelines 10.4.1. Expert Review guidelines
The appointed Expert should ensure that the proposed algorithm has a The appointed Expert should ensure that the proposed algorithm has a
public specification and is suitable for use as a cryptographic public specification, has a value assigned to it in the TLS
signature algorithm that always generates signatures SignatureScheme Registry (that IANA is asked to establish in
deterministically (for the reasons listed in Section 11.4). [I-D.ietf-tls-tls13]) and is suitable for use as a cryptographic
signature algorithm.
10.5. VersionedTransTypes 10.5. VersionedTransTypes
IANA is asked to establish a registry of "VersionedTransType" values, IANA is asked to establish a registry of "VersionedTransType" values,
named "CT VersionedTransTypes", that initially consists of: named "CT VersionedTransTypes", that initially consists of:
+------------+---------------------------+--------------------------+ +-------------+----------------------+------------------------------+
| Value | Type and Version | Reference / Assignment | | Value | Type and Version | Reference / Assignment |
| | | Policy | | | | Policy |
+------------+---------------------------+--------------------------+ +-------------+----------------------+------------------------------+
| 0x0000 | Reserved | [RFC6962] (*) | | 0x0000 | Reserved | [RFC6962] (*) |
| | | | | | | |
| 0x0001 | x509_entry_v2 | RFCXXXX | | 0x0001 | x509_entry_v2 | RFCXXXX |
| | | | | | | |
| 0x0002 | precert_entry_v2 | RFCXXXX | | 0x0002 | precert_entry_v2 | RFCXXXX |
| | | | | | | |
| 0x0003 | x509_sct_v2 | RFCXXXX | | 0x0003 | x509_sct_v2 | RFCXXXX |
| | | | | | | |
| 0x0004 | precert_sct_v2 | RFCXXXX | | 0x0004 | precert_sct_v2 | RFCXXXX |
| | | | | | | |
| 0x0005 | signed_tree_head_v2 | RFCXXXX | | 0x0005 | signed_tree_head_v2 | RFCXXXX |
| | | | | | | |
| 0x0006 | consistency_proof_v2 | RFCXXXX | | 0x0006 | consistency_proof_v2 | RFCXXXX |
| | | | | | | |
| 0x0007 | inclusion_proof_v2 | RFCXXXX | | 0x0007 | inclusion_proof_v2 | RFCXXXX |
| | | | | | | |
| 0x0008 | x509_sct_with_proof_v2 | RFCXXXX | | 0x0008 - | Unassigned | Specification Required and |
| | | | | 0xDFFF | | Expert Review |
| 0x0009 | precert_sct_with_proof_v2 | RFCXXXX | | | | |
| | | | | 0xE000 - | Reserved | Experimental Use |
| 0x0010 - | Unassigned | Specification Required | | 0xEFFF | | |
| 0xDFFF | | and Expert Review | | | | |
| | | | | 0xF000 - | Reserved | Private Use |
| 0xE000 - | Reserved | Experimental Use | | 0xFFFF | | |
| 0xEFFF | | | +-------------+----------------------+------------------------------+
| | | |
| 0xF000 - | Reserved | Private Use |
| 0xFFFF | | |
+------------+---------------------------+--------------------------+
(*) The 0x0000 value is reserved so that v1 SCTs are distinguishable (*) The 0x0000 value is reserved so that v1 SCTs are distinguishable
from v2 SCTs and other "TransItem" structures. from v2 SCTs and other "TransItem" structures.
[RFC Editor: please update 'RFCXXXX' to refer to this document, once [RFC Editor: please update 'RFCXXXX' to refer to this document, once
its RFC number is known.] its RFC number is known.]
10.5.1. Expert Review guidelines 10.5.1. Expert Review guidelines
The appointed Expert should review the public specification to ensure The appointed Expert should review the public specification to ensure
that it is detailed enough to ensure implementation interoperability. that it is detailed enough to ensure implementation interoperability.
10.6. SCT Extensions 10.6. Log Artifact Extension Registry
IANA is asked to establish a registry of SCT extensions, named "CT
Extension Types for SCT", that initially consists of:
+----------------+------------+-------------------------------------+
| Value | Extension | Reference / Assignment Policy |
+----------------+------------+-------------------------------------+
| 0x0000 - | Unassigned | Specification Required and Expert |
| 0xDFFF | | Review |
| | | |
| 0xE000 - | Reserved | Experimental Use |
| 0xEFFF | | |
| | | |
| 0xF000 - | Reserved | Private Use |
| 0xFFFF | | |
+----------------+------------+-------------------------------------+
10.6.1. Expert Review guidelines IANA is asked to establish a registry of "ExtensionType" values,
named "CT Log Artifact Extensions", that initially consists of:
The appointed Expert should review the public specification to ensure +---------------+------------+-----+--------------------------------+
that it is detailed enough to ensure implementation interoperability. | ExtensionType | Status | Use | Reference / Assignment Policy |
+---------------+------------+-----+--------------------------------+
| 0x0000 - | Unassigned | n/a | Specification Required and |
| 0xDFFF | | | Expert Review |
| | | | |
| 0xE000 - | Reserved | n/a | Experimental Use |
| 0xEFFF | | | |
| | | | |
| 0xF000 - | Reserved | n/a | Private Use |
| 0xFFFF | | | |
+---------------+------------+-----+--------------------------------+
10.7. STH Extensions The "Use" column should contain one or both of the following values:
IANA is asked to establish a registry of STH extensions, named "CT o "SCT", for extensions specified for use in Signed Certificate
Extension Types for STH", that initially consists of: Timestamps.
+----------------+------------+-------------------------------------+ o "STH", for extensions specified for use in Signed Tree Heads.
| Value | Extension | Reference / Assignment Policy |
+----------------+------------+-------------------------------------+
| 0x0000 - | Unassigned | Specification Required and Expert |
| 0xDFFF | | Review |
| | | |
| 0xE000 - | Reserved | Experimental Use |
| 0xEFFF | | |
| | | |
| 0xF000 - | Reserved | Private Use |
| 0xFFFF | | |
+----------------+------------+-------------------------------------+
10.7.1. Expert Review guidelines 10.6.1. Expert Review guidelines
The appointed Expert should review the public specification to ensure The appointed Expert should review the public specification to ensure
that it is detailed enough to ensure implementation interoperability. that it is detailed enough to ensure implementation interoperability.
The Expert should also verify that the extension is appropriate to
the contexts in which it is specified to be used (SCT, STH, or both).
10.8. Object Identifiers 10.7. Object Identifiers
This document uses object identifiers (OIDs) to identify Log IDs (see This document uses object identifiers (OIDs) to identify Log IDs (see
Section 4.3), the precertificate CMS "eContentType" (see Section 4.4), the precertificate CMS "eContentType" (see
Section 3.2), and X.509v3 extensions in certificates (see Section 3.2), and X.509v3 extensions in certificates (see
Section 7.1.2) and OCSP responses (see Section 7.1.1). The OIDs are Section 7.1.2) and OCSP responses (see Section 7.1.1). The OIDs are
defined in an arc that was selected due to its short encoding. defined in an arc that was selected due to its short encoding.
10.8.1. Log ID Registry 10.7.1. Log ID Registry
IANA is asked to establish a registry of Log IDs, named "CT Log ID IANA is asked to establish a registry of Log IDs, named "CT Log ID
Registry", that initially consists of: Registry", that initially consists of:
+-------------------------+------------+----------------------------+ +------------------------+------------+-----------------------------+
| Value | Log | Reference / Assignment | | Value | Log | Reference / Assignment |
| | | Policy | | | | Policy |
+-------------------------+------------+----------------------------+ +------------------------+------------+-----------------------------+
| 1.3.101.8192 - | Unassigned | Metadata Required and | | 1.3.101.8192 - | Unassigned | Parameters Required and |
| 1.3.101.16383 | | Expert Review | | 1.3.101.16383 | | Expert Review |
| | | | | | | |
| 1.3.101.80.0 - | Unassigned | Metadata Required and | | 1.3.101.80.0 - | Unassigned | Parameters Required and |
| 1.3.101.80.127 | | Expert Review | | 1.3.101.80.127 | | Expert Review |
| | | | | | | |
| 1.3.101.80.128 - | Unassigned | First Come First Served | | 1.3.101.80.128 - | Unassigned | First Come First Served |
| 1.3.101.80.* | | | | 1.3.101.80.* | | |
+-------------------------+------------+----------------------------+ +------------------------+------------+-----------------------------+
All OIDs in the range from 1.3.101.8192 to 1.3.101.16383 have been All OIDs in the range from 1.3.101.8192 to 1.3.101.16383 have been
reserved. This is a limited resource of 8,192 OIDs, each of which reserved. This is a limited resource of 8,192 OIDs, each of which
has an encoded length of 4 octets. has an encoded length of 4 octets.
The 1.3.101.80 arc has been delegated. This is an unlimited The 1.3.101.80 arc has been delegated. This is an unlimited
resource, but only the 128 OIDs from 1.3.101.80.0 to 1.3.101.80.127 resource, but only the 128 OIDs from 1.3.101.80.0 to 1.3.101.80.127
have an encoded length of only 4 octets. have an encoded length of only 4 octets.
Each application for the allocation of a Log ID should be accompanied Each application for the allocation of a Log ID should be accompanied
by all of the required metadata (except for the Log ID) listed in by all of the required parameters (except for the Log ID) listed in
Section 8.1. Section 4.1.
10.8.2. Expert Review guidelines 10.7.2. Expert Review guidelines
Since the Log IDs with the shortest encodings are a limited resource, Since the Log IDs with the shortest encodings are a limited resource,
the appointed Expert should review the submitted metadata and judge the appointed Expert should review the submitted parameters and judge
whether or not the applicant is requesting a Log ID in good faith whether or not the applicant is requesting a Log ID in good faith
(with the intention of actually running a CT log that will be (with the intention of actually running a CT log that will be
identified by the allocated Log ID). identified by the allocated Log ID).
11. Security Considerations 11. Security Considerations
With CAs, logs, and servers performing the actions described here, With CAs, logs, and servers performing the actions described here,
TLS clients can use logs and signed timestamps to reduce the TLS clients can use logs and signed timestamps to reduce the
likelihood that they will accept misissued certificates. If a server likelihood that they will accept misissued certificates. If a server
presents a valid signed timestamp for a certificate, then the client presents a valid signed timestamp for a certificate, then the client
skipping to change at page 48, line 34 skipping to change at page 48, line 19
[I-D.ietf-trans-threat-analysis] provides a more detailed threat [I-D.ietf-trans-threat-analysis] provides a more detailed threat
analysis of the Certificate Transparency architecture. analysis of the Certificate Transparency architecture.
11.1. Misissued Certificates 11.1. Misissued Certificates
Misissued certificates that have not been publicly logged, and thus Misissued certificates that have not been publicly logged, and thus
do not have a valid SCT, are not considered compliant. Misissued do not have a valid SCT, are not considered compliant. Misissued
certificates that do have an SCT from a log will appear in that certificates that do have an SCT from a log will appear in that
public log within the Maximum Merge Delay, assuming the log is public log within the Maximum Merge Delay, assuming the log is
operating correctly. Thus, the maximum period of time during which a operating correctly. As a log is allowed to serve an STH that's up
misissued certificate can be used without being available for audit to MMD old, the maximum period of time during which a misissued
is the MMD. certificate can be used without being available for audit is twice
the MMD.
11.2. Detection of Misissue 11.2. Detection of Misissue
The logs do not themselves detect misissued certificates; they rely The logs do not themselves detect misissued certificates; they rely
instead on interested parties, such as domain owners, to monitor them instead on interested parties, such as domain owners, to monitor them
and take corrective action when a misissue is detected. and take corrective action when a misissue is detected.
11.3. Misbehaving Logs 11.3. Misbehaving Logs
A log can misbehave in several ways. Examples include failing to A log can misbehave in several ways. Examples include: failing to
incorporate a certificate with an SCT in the Merkle Tree within the incorporate a certificate with an SCT in the Merkle Tree within the
MMD, presenting different, conflicting views of the Merkle Tree at MMD; presenting different, conflicting views of the Merkle Tree at
different times and/or to different parties and issuing STHs too different times and/or to different parties; and issuing STHs too
frequently. Such misbehavior is detectable and the frequently. Such misbehavior is detectable and
[I-D.ietf-trans-threat-analysis] provides more details on how this [I-D.ietf-trans-threat-analysis] provides more details on how this
can be done. can be done.
Violation of the MMD contract is detected by log clients requesting a Violation of the MMD contract is detected by log clients requesting a
Merkle inclusion proof (Section 5.5) for each observed SCT. These Merkle inclusion proof (Section 5.4) for each observed SCT. These
checks can be asynchronous and need only be done once per each checks can be asynchronous and need only be done once per
certificate. In order to protect the clients' privacy, these checks certificate. In order to protect the clients' privacy, these checks
need not reveal the exact certificate to the log. Instead, clients need not reveal the exact certificate to the log. Instead, clients
can request the proof from a trusted auditor (since anyone can can request the proof from a trusted auditor (since anyone can
compute the proofs from the log) or communicate with the log via compute the proofs from the log) or communicate with the log via
proxies. proxies.
Violation of the append-only property or the STH issuance rate limit Violation of the append-only property or the STH issuance rate limit
can be detected by clients comparing their instances of the Signed can be detected by clients comparing their instances of the Signed
Tree Heads. There are various ways this could be done, for example Tree Heads. There are various ways this could be done, for example
via gossip (see [I-D.ietf-trans-gossip]) or peer-to-peer via gossip (see [I-D.ietf-trans-gossip]) or peer-to-peer
communications or by sending STHs to monitors (who could then communications or by sending STHs to monitors (who could then
directly check against their own copy of the relevant log). A proof directly check against their own copy of the relevant log). Proof of
of misbehavior in such cases would be a series of STHs that were misbehavior in such cases would be: a series of STHs that were issued
issued too closely together, proving violation of the STH issuance too closely together, proving violation of the STH issuance rate
rate limit, or an STH with a root hash that does not match the one limit; or an STH with a root hash that does not match the one
calculated from a copy of the log, proving violation of the append- calculated from a copy of the log, proving violation of the append-
only property. only property.
11.4. Deterministic Signatures 11.4. Preventing Tracking Clients
Logs are required to use deterministic signatures for the following Clients that gossip STHs or report back SCTs can be tracked or traced
reasons: if a log produces multiple STHs or SCTs with the same timestamp and
data but different signatures. Logs SHOULD mitigate this risk by
either:
o Using non-deterministic ECDSA with a predictable source of o Using deterministic signature schemes, or
randomness means that each signature can potentially expose the
secret material of the signing key.
o Clients that gossip STHs or report back SCTs can be tracked or o Producing no more than one SCT for each distinct submission and no
traced if a log was to produce multiple STHs or SCTs with the same more than one STH for each distinct tree_size. Each of these SCTs
timestamp and data but different signatures. and STHs can be stored by the log and served to other clients that
submit the same certificate or request the same STH.
11.5. Multiple SCTs 11.5. Multiple SCTs
By offering multiple SCTs, each from a different log, TLS servers By offering multiple SCTs, each from a different log, TLS servers
reduce the effectiveness of an attack where a CA and a log collude reduce the effectiveness of an attack where a CA and a log collude
(see Section 6.1). (see Section 6.1).
12. Acknowledgements 12. Acknowledgements
The authors would like to thank Erwann Abelea, Robin Alden, Andrew The authors would like to thank Erwann Abelea, Robin Alden, Andrew
Ayer, Al Cutter, David Drysdale, Francis Dupont, Adam Eijdenberg, Ayer, Richard Barnes, Al Cutter, David Drysdale, Francis Dupont, Adam
Stephen Farrell, Daniel Kahn Gillmor, Paul Hadfield, Brad Hill, Jeff Eijdenberg, Stephen Farrell, Daniel Kahn Gillmor, Paul Hadfield, Brad
Hodges, Paul Hoffman, Jeffrey Hutzelman, Kat Joyce, Stephen Kent, SM, Hill, Jeff Hodges, Paul Hoffman, Jeffrey Hutzelman, Kat Joyce,
Alexey Melnikov, Linus Nordberg, Chris Palmer, Trevor Perrin, Pierre Stephen Kent, SM, Alexey Melnikov, Linus Nordberg, Chris Palmer,
Phaneuf, Melinda Shore, Ryan Sleevi, Martin Smith, Carl Wallace and Trevor Perrin, Pierre Phaneuf, Eric Rescorla, Melinda Shore, Ryan
Paul Wouters for their valuable contributions. Sleevi, Martin Smith, Carl Wallace and Paul Wouters for their
valuable contributions.
A big thank you to Symantec for kindly donating the OIDs from the A big thank you to Symantec for kindly donating the OIDs from the
1.3.101 arc that are used in this document. 1.3.101 arc that are used in this document.
13. References 13. References
13.1. Normative References 13.1. Normative References
[FIPS186-4]
NIST, "FIPS PUB 186-4", July 2013,
<http://nvlpubs.nist.gov/nistpubs/FIPS/
NIST.FIPS.186-4.pdf>.
[HTML401] Raggett, D., Le Hors, A., and I. Jacobs, "HTML 4.01 [HTML401] Raggett, D., Le Hors, A., and I. Jacobs, "HTML 4.01
Specification", World Wide Web Consortium Recommendation Specification", World Wide Web Consortium Recommendation
REC-html401-19991224, December 1999, REC-html401-19991224, December 1999,
<http://www.w3.org/TR/1999/REC-html401-19991224>. <http://www.w3.org/TR/1999/REC-html401-19991224>.
[I-D.ietf-tls-tls13]
Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", draft-ietf-tls-tls13-20 (work in progress),
April 2017.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/ Requirement Levels", BCP 14, RFC 2119,
RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>. <http://www.rfc-editor.org/info/rfc2119>.
[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data [RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006, Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
<http://www.rfc-editor.org/info/rfc4648>. <http://www.rfc-editor.org/info/rfc4648>.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, DOI 10.17487/ (TLS) Protocol Version 1.2", RFC 5246,
RFC5246, August 2008, DOI 10.17487/RFC5246, August 2008,
<http://www.rfc-editor.org/info/rfc5246>. <http://www.rfc-editor.org/info/rfc5246>.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S., [RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008, (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
<http://www.rfc-editor.org/info/rfc5280>. <http://www.rfc-editor.org/info/rfc5280>.
[RFC5652] Housley, R., "Cryptographic Message Syntax (CMS)", STD 70, [RFC5652] Housley, R., "Cryptographic Message Syntax (CMS)", STD 70,
RFC 5652, DOI 10.17487/RFC5652, September 2009, RFC 5652, DOI 10.17487/RFC5652, September 2009,
<http://www.rfc-editor.org/info/rfc5652>. <http://www.rfc-editor.org/info/rfc5652>.
[RFC5905] Mills, D., Martin, J., Ed., Burbank, J., and W. Kasch, [RFC5905] Mills, D., Martin, J., Ed., Burbank, J., and W. Kasch,
"Network Time Protocol Version 4: Protocol and Algorithms "Network Time Protocol Version 4: Protocol and Algorithms
Specification", RFC 5905, DOI 10.17487/RFC5905, June 2010, Specification", RFC 5905, DOI 10.17487/RFC5905, June 2010,
<http://www.rfc-editor.org/info/rfc5905>. <http://www.rfc-editor.org/info/rfc5905>.
[RFC6066] Eastlake 3rd, D., "Transport Layer Security (TLS) [RFC6066] Eastlake 3rd, D., "Transport Layer Security (TLS)
Extensions: Extension Definitions", RFC 6066, DOI 10.17487 Extensions: Extension Definitions", RFC 6066,
/RFC6066, January 2011, DOI 10.17487/RFC6066, January 2011,
<http://www.rfc-editor.org/info/rfc6066>. <http://www.rfc-editor.org/info/rfc6066>.
[RFC6960] Santesson, S., Myers, M., Ankney, R., Malpani, A., [RFC6960] Santesson, S., Myers, M., Ankney, R., Malpani, A.,
Galperin, S., and C. Adams, "X.509 Internet Public Key Galperin, S., and C. Adams, "X.509 Internet Public Key
Infrastructure Online Certificate Status Protocol - OCSP", Infrastructure Online Certificate Status Protocol - OCSP",
RFC 6960, DOI 10.17487/RFC6960, June 2013, RFC 6960, DOI 10.17487/RFC6960, June 2013,
<http://www.rfc-editor.org/info/rfc6960>. <http://www.rfc-editor.org/info/rfc6960>.
[RFC6961] Pettersen, Y., "The Transport Layer Security (TLS) [RFC6961] Pettersen, Y., "The Transport Layer Security (TLS)
Multiple Certificate Status Request Extension", RFC 6961, Multiple Certificate Status Request Extension", RFC 6961,
DOI 10.17487/RFC6961, June 2013, DOI 10.17487/RFC6961, June 2013,
<http://www.rfc-editor.org/info/rfc6961>. <http://www.rfc-editor.org/info/rfc6961>.
[RFC7159] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data [RFC7159] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
Interchange Format", RFC 7159, DOI 10.17487/RFC7159, March Interchange Format", RFC 7159, DOI 10.17487/RFC7159, March
2014, <http://www.rfc-editor.org/info/rfc7159>. 2014, <http://www.rfc-editor.org/info/rfc7159>.
[RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer [RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Semantics and Content", RFC 7231, DOI Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
10.17487/RFC7231, June 2014, DOI 10.17487/RFC7231, June 2014,
<http://www.rfc-editor.org/info/rfc7231>. <http://www.rfc-editor.org/info/rfc7231>.
[RFC7633] Hallam-Baker, P., "X.509v3 Transport Layer Security (TLS) [RFC7633] Hallam-Baker, P., "X.509v3 Transport Layer Security (TLS)
Feature Extension", RFC 7633, DOI 10.17487/RFC7633, Feature Extension", RFC 7633, DOI 10.17487/RFC7633,
October 2015, <http://www.rfc-editor.org/info/rfc7633>. October 2015, <http://www.rfc-editor.org/info/rfc7633>.
[RFC7924] Santesson, S. and H. Tschofenig, "Transport Layer Security [RFC7924] Santesson, S. and H. Tschofenig, "Transport Layer Security
(TLS) Cached Information Extension", RFC 7924, DOI (TLS) Cached Information Extension", RFC 7924,
10.17487/RFC7924, July 2016, DOI 10.17487/RFC7924, July 2016,
<http://www.rfc-editor.org/info/rfc7924>. <http://www.rfc-editor.org/info/rfc7924>.
[RFC8017] Moriarty, K., Ed., Kaliski, B., Jonsson, J., and A. Rusch, [RFC8032] Josefsson, S. and I. Liusvaara, "Edwards-Curve Digital
"PKCS #1: RSA Cryptography Specifications Version 2.2", Signature Algorithm (EdDSA)", RFC 8032,
RFC 8017, DOI 10.17487/RFC8017, November 2016, DOI 10.17487/RFC8032, January 2017,
<http://www.rfc-editor.org/info/rfc8017>. <http://www.rfc-editor.org/info/rfc8032>.
13.2. Informative References 13.2. Informative References
[Chromium.Log.Policy] [Chromium.Log.Policy]
The Chromium Projects, "Chromium Certificate Transparency The Chromium Projects, "Chromium Certificate Transparency
Log Policy", 2014, <http://www.chromium.org/Home/ Log Policy", 2014, <http://www.chromium.org/Home/chromium-
chromium-security/certificate-transparency/log-policy>. security/certificate-transparency/log-policy>.
[Chromium.Policy] [Chromium.Policy]
The Chromium Projects, "Chromium Certificate The Chromium Projects, "Chromium Certificate
Transparency", 2014, <http://www.chromium.org/Home/ Transparency", 2014, <http://www.chromium.org/Home/
chromium-security/certificate-transparency>. chromium-security/certificate-transparency>.
[CrosbyWallach] [CrosbyWallach]
Crosby, S. and D. Wallach, "Efficient Data Structures for Crosby, S. and D. Wallach, "Efficient Data Structures for
Tamper-Evident Logging", Proceedings of the 18th USENIX Tamper-Evident Logging", Proceedings of the 18th USENIX
Security Symposium, Montreal, August 2009, Security Symposium, Montreal, August 2009,
<http://static.usenix.org/event/sec09/tech/full_papers/ <http://static.usenix.org/event/sec09/tech/full_papers/
crosby.pdf>. crosby.pdf>.
[I-D.ietf-trans-gossip] [I-D.ietf-trans-gossip]
Nordberg, L., Gillmor, D., and T. Ritter, "Gossiping in Nordberg, L., Gillmor, D., and T. Ritter, "Gossiping in
CT", draft-ietf-trans-gossip-03 (work in progress), July CT", draft-ietf-trans-gossip-04 (work in progress),
2016. January 2017.
[I-D.ietf-trans-threat-analysis] [I-D.ietf-trans-threat-analysis]
Kent, S., "Attack and Threat Model for Certificate Kent, S., "Attack and Threat Model for Certificate
Transparency", draft-ietf-trans-threat-analysis-10 (work Transparency", draft-ietf-trans-threat-analysis-11 (work
in progress), October 2016. in progress), April 2017.
[JSON.Metadata] [JSON.Metadata]
The Chromium Projects, "Chromium Log Metadata JSON The Chromium Projects, "Chromium Log Metadata JSON
Schema", 2014, <http://www.certificate-transparency.org/ Schema", 2014, <http://www.certificate-transparency.org/
known-logs/log_list_schema.json>. known-logs/log_list_schema.json>.
[RFC4634] Eastlake 3rd, D. and T. Hansen, "US Secure Hash Algorithms
(SHA and HMAC-SHA)", RFC 4634, DOI 10.17487/RFC4634, July
2006, <http://www.rfc-editor.org/info/rfc4634>.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226, IANA Considerations Section in RFCs", RFC 5226,
DOI 10.17487/RFC5226, May 2008, DOI 10.17487/RFC5226, May 2008,
<http://www.rfc-editor.org/info/rfc5226>. <http://www.rfc-editor.org/info/rfc5226>.
[RFC6234] Eastlake 3rd, D. and T. Hansen, "US Secure Hash Algorithms
(SHA and SHA-based HMAC and HKDF)", RFC 6234,
DOI 10.17487/RFC6234, May 2011,
<http://www.rfc-editor.org/info/rfc6234>.
[RFC6962] Laurie, B., Langley, A., and E. Kasper, "Certificate [RFC6962] Laurie, B., Langley, A., and E. Kasper, "Certificate
Transparency", RFC 6962, DOI 10.17487/RFC6962, June 2013, Transparency", RFC 6962, DOI 10.17487/RFC6962, June 2013,
<http://www.rfc-editor.org/info/rfc6962>. <http://www.rfc-editor.org/info/rfc6962>.
[RFC6979] Pornin, T., "Deterministic Usage of the Digital Signature [RFC6979] Pornin, T., "Deterministic Usage of the Digital Signature
Algorithm (DSA) and Elliptic Curve Digital Signature Algorithm (DSA) and Elliptic Curve Digital Signature
Algorithm (ECDSA)", RFC 6979, DOI 10.17487/RFC6979, August Algorithm (ECDSA)", RFC 6979, DOI 10.17487/RFC6979, August
2013, <http://www.rfc-editor.org/info/rfc6979>. 2013, <http://www.rfc-editor.org/info/rfc6979>.
[RFC7320] Nottingham, M., "URI Design and Ownership", BCP 190,
RFC 7320, DOI 10.17487/RFC7320, July 2014,
<http://www.rfc-editor.org/info/rfc7320>.
Appendix A. Supporting v1 and v2 simultaneously Appendix A. Supporting v1 and v2 simultaneously
Certificate Transparency logs have to be either v1 (conforming to Certificate Transparency logs have to be either v1 (conforming to
[RFC6962]) or v2 (conforming to this document), as the data [RFC6962]) or v2 (conforming to this document), as the data
structures are incompatible and so a v2 log could not issue a valid structures are incompatible and so a v2 log could not issue a valid
v1 SCT. v1 SCT.
CT clients, however, can support v1 and v2 SCTs, for the same CT clients, however, can support v1 and v2 SCTs, for the same
certificate, simultaneously, as v1 SCTs are delivered in different certificate, simultaneously, as v1 SCTs are delivered in different
TLS, X.509 and OCSP extensions than v2 SCTs. TLS, X.509 and OCSP extensions than v2 SCTs.
skipping to change at page 53, line 27 skipping to change at page 53, line 38
o Create a CMS precertificate as described in Section 3.2 and submit o Create a CMS precertificate as described in Section 3.2 and submit
it to v2 logs. it to v2 logs.
o Embed the obtained v2 SCTs in the TBSCertificate, as described in o Embed the obtained v2 SCTs in the TBSCertificate, as described in
Section 7.1.2. Section 7.1.2.
o Use that TBSCertificate to create a v1 precertificate, as o Use that TBSCertificate to create a v1 precertificate, as
described in Section 3.1. of [RFC6962] and submit it to v1 logs. described in Section 3.1. of [RFC6962] and submit it to v1 logs.
o Embed the v1 SCTs in the TBSCertificate, as described in o Embed the v1 SCTs in the TBSCertificate, as described in
Section 3.3. of [RFC6962]. Section 3.3 of [RFC6962].
o Sign that TBSCertificate (which now contains v1 and v2 SCTs) to o Sign that TBSCertificate (which now contains v1 and v2 SCTs) to
issue the final X.509 certificate. issue the final X.509 certificate.
Authors' Addresses Authors' Addresses
Ben Laurie Ben Laurie
Google UK Ltd. Google UK Ltd.
Email: benl@google.com Email: benl@google.com
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