draft-ietf-trans-rfc6962-bis-14.txt   draft-ietf-trans-rfc6962-bis-15.txt 
Public Notary Transparency Working Group B. Laurie Public Notary Transparency Working Group B. Laurie
Internet-Draft A. Langley Internet-Draft A. Langley
Intended status: Standards Track E. Kasper Intended status: Standards Track E. Kasper
Expires: October 13, 2016 E. Messeri Expires: November 27, 2016 E. Messeri
Google Google
R. Stradling R. Stradling
Comodo Comodo
April 11, 2016 May 26, 2016
Certificate Transparency Certificate Transparency
draft-ietf-trans-rfc6962-bis-14 draft-ietf-trans-rfc6962-bis-15
Abstract Abstract
This document describes a protocol for publicly logging the existence This document describes a protocol for publicly logging the existence
of Transport Layer Security (TLS) certificates as they are issued or of Transport Layer Security (TLS) certificates as they are issued or
observed, in a manner that allows anyone to audit certification observed, in a manner that allows anyone to audit certification
authority (CA) activity and notice the issuance of suspect authority (CA) activity and notice the issuance of suspect
certificates as well as to audit the certificate logs themselves. certificates as well as to audit the certificate logs themselves.
The intent is that eventually clients would refuse to honor The intent is that eventually clients would refuse to honor
certificates that do not appear in a log, effectively forcing CAs to certificates that do not appear in a log, effectively forcing CAs to
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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 October 13, 2016. This Internet-Draft will expire on November 27, 2016.
Copyright Notice Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
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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
2. Cryptographic Components . . . . . . . . . . . . . . . . . . 5 2. Cryptographic Components . . . . . . . . . . . . . . . . . . 5
2.1. Merkle Hash Trees . . . . . . . . . . . . . . . . . . . . 5 2.1. Merkle Hash Trees . . . . . . . . . . . . . . . . . . . . 5
2.1.1. Merkle Inclusion Proofs . . . . . . . . . . . . . . . 6 2.1.1. Merkle Inclusion Proofs . . . . . . . . . . . . . . . 6
2.1.2. Merkle Consistency Proofs . . . . . . . . . . . . . . 7 2.1.2. Merkle Consistency Proofs . . . . . . . . . . . . . . 7
2.1.3. Example . . . . . . . . . . . . . . . . . . . . . . . 8 2.1.3. Example . . . . . . . . . . . . . . . . . . . . . . . 8
2.1.4. Signatures . . . . . . . . . . . . . . . . . . . . . 9 2.1.4. Signatures . . . . . . . . . . . . . . . . . . . . . 10
3. Submitters . . . . . . . . . . . . . . . . . . . . . . . . . 10 3. Submitters . . . . . . . . . . . . . . . . . . . . . . . . . 11
3.1. Certificates . . . . . . . . . . . . . . . . . . . . . . 10 3.1. Certificates . . . . . . . . . . . . . . . . . . . . . . 11
3.2. Precertificates . . . . . . . . . . . . . . . . . . . . . 10 3.2. Precertificates . . . . . . . . . . . . . . . . . . . . . 11
4. Private Domain Name Labels . . . . . . . . . . . . . . . . . 11 4. Private Domain Name Labels . . . . . . . . . . . . . . . . . 12
4.1. Wildcard Certificates . . . . . . . . . . . . . . . . . . 11 4.1. Wildcard Certificates . . . . . . . . . . . . . . . . . . 12
4.2. Redaction of Domain Name Labels . . . . . . . . . . . . . 11 4.2. Redaction of Domain Name Labels . . . . . . . . . . . . . 12
4.2.1. Redacting Labels in Precertificates . . . . . . . . . 12 4.2.1. Redacting Labels in Precertificates . . . . . . . . . 13
4.2.2. Redacted Labels Certificate Extension . . . . . . . . 12 4.2.2. Redacted Labels Certificate Extension . . . . . . . . 13
4.3. Using a Name-Constrained Intermediate CA . . . . . . . . 12 4.3. Using a Name-Constrained Intermediate CA . . . . . . . . 13
5. Log Format and Operation . . . . . . . . . . . . . . . . . . 13 5. Log Format and Operation . . . . . . . . . . . . . . . . . . 14
5.1. Accepting Submissions . . . . . . . . . . . . . . . . . . 14 5.1. Accepting Submissions . . . . . . . . . . . . . . . . . . 15
5.2. Log Entries . . . . . . . . . . . . . . . . . . . . . . . 14 5.2. Log Entries . . . . . . . . . . . . . . . . . . . . . . . 15
5.3. Log ID . . . . . . . . . . . . . . . . . . . . . . . . . 15 5.3. Log ID . . . . . . . . . . . . . . . . . . . . . . . . . 16
5.4. TransItem Structure . . . . . . . . . . . . . . . . . . . 16 5.4. TransItem Structure . . . . . . . . . . . . . . . . . . . 17
5.5. Merkle Tree Leaves . . . . . . . . . . . . . . . . . . . 17 5.5. Merkle Tree Leaves . . . . . . . . . . . . . . . . . . . 18
5.6. Signed Certificate Timestamp (SCT) . . . . . . . . . . . 18 5.6. Signed Certificate Timestamp (SCT) . . . . . . . . . . . 19
5.7. Merkle Tree Head . . . . . . . . . . . . . . . . . . . . 19 5.7. Merkle Tree Head . . . . . . . . . . . . . . . . . . . . 20
5.8. Signed Tree Head (STH) . . . . . . . . . . . . . . . . . 19 5.8. Signed Tree Head (STH) . . . . . . . . . . . . . . . . . 20
5.9. Merkle Consistency Proofs . . . . . . . . . . . . . . . . 21 5.9. Merkle Consistency Proofs . . . . . . . . . . . . . . . . 22
5.10. Merkle Inclusion Proofs . . . . . . . . . . . . . . . . . 21 5.10. Merkle Inclusion Proofs . . . . . . . . . . . . . . . . . 22
5.11. Shutting down a log . . . . . . . . . . . . . . . . . . . 22 5.11. Shutting down a log . . . . . . . . . . . . . . . . . . . 23
6. Log Client Messages . . . . . . . . . . . . . . . . . . . . . 22 6. Log Client Messages . . . . . . . . . . . . . . . . . . . . . 23
6.1. Add Chain to Log . . . . . . . . . . . . . . . . . . . . 24 6.1. Add Chain to Log . . . . . . . . . . . . . . . . . . . . 25
6.2. Add PreCertChain to Log . . . . . . . . . . . . . . . . . 25 6.2. Add PreCertChain to Log . . . . . . . . . . . . . . . . . 26
6.3. Retrieve Latest Signed Tree Head . . . . . . . . . . . . 25 6.3. Retrieve Latest Signed Tree Head . . . . . . . . . . . . 26
6.4. Retrieve Merkle Consistency Proof between Two Signed Tree 6.4. Retrieve Merkle Consistency Proof between Two Signed Tree
Heads . . . . . . . . . . . . . . . . . . . . . . . . . . 26 Heads . . . . . . . . . . . . . . . . . . . . . . . . . . 26
6.5. Retrieve Merkle Inclusion Proof from Log by Leaf Hash . . 27 6.5. Retrieve Merkle Inclusion Proof from Log by Leaf Hash . . 27
6.6. Retrieve Merkle Inclusion Proof, Signed Tree Head and 6.6. Retrieve Merkle Inclusion Proof, Signed Tree Head and
Consistency Proof by Leaf Hash . . . . . . . . . . . . . 28 Consistency Proof by Leaf Hash . . . . . . . . . . . . . 28
6.7. Retrieve Entries and STH from Log . . . . . . . . . . . . 29 6.7. Retrieve Entries and STH from Log . . . . . . . . . . . . 29
6.8. Retrieve Accepted Trust Anchors . . . . . . . . . . . . . 30 6.8. Get Entry Number for SCT . . . . . . . . . . . . . . . . 31
7. TLS Servers . . . . . . . . . . . . . . . . . . . . . . . . . 31 6.9. Retrieve Accepted Trust Anchors . . . . . . . . . . . . . 31
7.1. Multiple SCTs . . . . . . . . . . . . . . . . . . . . . . 31 7. Optional Client Messages . . . . . . . . . . . . . . . . . . 32
7.2. TransItemList Structure . . . . . . . . . . . . . . . . . 32 7.1. Get Entry Number for SCT . . . . . . . . . . . . . . . . 32
7.3. Presenting SCTs, inclusion proofs and STHs . . . . . . . 32 7.2. Get Entry Numbers for Certificate . . . . . . . . . . . . 32
7.4. Presenting SCTs only . . . . . . . . . . . . . . . . . . 33 8. TLS Servers . . . . . . . . . . . . . . . . . . . . . . . . . 33
7.5. transparency_info TLS Extension . . . . . . . . . . . . . 33 8.1. Multiple SCTs . . . . . . . . . . . . . . . . . . . . . . 34
8. Certification Authorities . . . . . . . . . . . . . . . . . . 33 8.2. TransItemList Structure . . . . . . . . . . . . . . . . . 34
8.1. Transparency Information X.509v3 Extension . . . . . . . 34 8.3. Presenting SCTs, inclusion proofs and STHs . . . . . . . 35
8.1.1. OCSP Response Extension . . . . . . . . . . . . . . . 34 8.4. Presenting SCTs only . . . . . . . . . . . . . . . . . . 35
8.1.2. Certificate Extension . . . . . . . . . . . . . . . . 34 8.5. transparency_info TLS Extension . . . . . . . . . . . . . 35
8.2. TLS Feature Extension . . . . . . . . . . . . . . . . . . 34 9. Certification Authorities . . . . . . . . . . . . . . . . . . 36
9. Clients . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 9.1. Transparency Information X.509v3 Extension . . . . . . . 36
9.1. Metadata . . . . . . . . . . . . . . . . . . . . . . . . 35 9.1.1. OCSP Response Extension . . . . . . . . . . . . . . . 36
9.2. TLS Client . . . . . . . . . . . . . . . . . . . . . . . 36 9.1.2. Certificate Extension . . . . . . . . . . . . . . . . 36
9.2.1. Receiving SCTs . . . . . . . . . . . . . . . . . . . 36 9.2. TLS Feature Extension . . . . . . . . . . . . . . . . . . 36
9.2.2. Reconstructing the TBSCertificate . . . . . . . . . . 36 10. Clients . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
9.2.3. Validating SCTs . . . . . . . . . . . . . . . . . . . 36 10.1. Metadata . . . . . . . . . . . . . . . . . . . . . . . . 37
9.2.4. Validating inclusion proofs . . . . . . . . . . . . . 37 10.2. TLS Client . . . . . . . . . . . . . . . . . . . . . . . 38
9.2.5. Evaluating compliance . . . . . . . . . . . . . . . . 37 10.2.1. Receiving SCTs . . . . . . . . . . . . . . . . . . . 38
9.2.6. TLS Feature Extension . . . . . . . . . . . . . . . . 37 10.2.2. Reconstructing the TBSCertificate . . . . . . . . . 38
9.2.7. Handling of Non-compliance . . . . . . . . . . . . . 37 10.2.3. Validating SCTs . . . . . . . . . . . . . . . . . . 38
9.3. Monitor . . . . . . . . . . . . . . . . . . . . . . . . . 38 10.2.4. Validating inclusion proofs . . . . . . . . . . . . 39
9.4. Auditing . . . . . . . . . . . . . . . . . . . . . . . . 39 10.2.5. Evaluating compliance . . . . . . . . . . . . . . . 39
9.4.1. Verifying an inclusion proof . . . . . . . . . . . . 40 10.2.6. TLS Feature Extension . . . . . . . . . . . . . . . 39
9.4.2. Verifying consistency between two STHs . . . . . . . 40 10.2.7. Handling of Non-compliance . . . . . . . . . . . . . 40
9.4.3. Verifying root hash given entries . . . . . . . . . . 41 10.3. Monitor . . . . . . . . . . . . . . . . . . . . . . . . 40
10. Algorithm Agility . . . . . . . . . . . . . . . . . . . . . . 42 10.4. Auditing . . . . . . . . . . . . . . . . . . . . . . . . 41
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 43 10.4.1. Verifying an inclusion proof . . . . . . . . . . . . 42
11.1. TLS Extension Type . . . . . . . . . . . . . . . . . . . 43 10.4.2. Verifying consistency between two STHs . . . . . . . 43
11.2. Hash Algorithms . . . . . . . . . . . . . . . . . . . . 43 10.4.3. Verifying root hash given entries . . . . . . . . . 44
11.3. Signature Algorithms . . . . . . . . . . . . . . . . . . 43 11. Algorithm Agility . . . . . . . . . . . . . . . . . . . . . . 44
11.4. SCT Extensions . . . . . . . . . . . . . . . . . . . . . 43 12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 45
11.5. STH Extensions . . . . . . . . . . . . . . . . . . . . . 44 12.1. TLS Extension Type . . . . . . . . . . . . . . . . . . . 45
11.6. Object Identifiers . . . . . . . . . . . . . . . . . . . 44 12.2. Hash Algorithms . . . . . . . . . . . . . . . . . . . . 45
11.6.1. Log ID Registry 1 . . . . . . . . . . . . . . . . . 44 12.3. Signature Algorithms . . . . . . . . . . . . . . . . . . 45
11.6.2. Log ID Registry 2 . . . . . . . . . . . . . . . . . 44 12.4. SCT Extensions . . . . . . . . . . . . . . . . . . . . . 45
12. Security Considerations . . . . . . . . . . . . . . . . . . . 45 12.5. STH Extensions . . . . . . . . . . . . . . . . . . . . . 46
12.1. Misissued Certificates . . . . . . . . . . . . . . . . . 45 12.6. Object Identifiers . . . . . . . . . . . . . . . . . . . 46
12.2. Detection of Misissue . . . . . . . . . . . . . . . . . 45 12.6.1. Log ID Registry 1 . . . . . . . . . . . . . . . . . 46
12.3. Avoiding Overly Redacting Domain Name Labels . . . . . . 45 12.6.2. Log ID Registry 2 . . . . . . . . . . . . . . . . . 46
12.4. Misbehaving Logs . . . . . . . . . . . . . . . . . . . . 46 13. Security Considerations . . . . . . . . . . . . . . . . . . . 47
12.5. Deterministic Signatures . . . . . . . . . . . . . . . . 46 13.1. Misissued Certificates . . . . . . . . . . . . . . . . . 47
12.6. Multiple SCTs . . . . . . . . . . . . . . . . . . . . . 47 13.2. Detection of Misissue . . . . . . . . . . . . . . . . . 47
12.7. Threat Analysis . . . . . . . . . . . . . . . . . . . . 47 13.3. Avoiding Overly Redacting Domain Name Labels . . . . . . 47
13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 47 13.4. Misbehaving Logs . . . . . . . . . . . . . . . . . . . . 48
14. References . . . . . . . . . . . . . . . . . . . . . . . . . 47 13.5. Deterministic Signatures . . . . . . . . . . . . . . . . 48
14.1. Normative References . . . . . . . . . . . . . . . . . . 47 13.6. Multiple SCTs . . . . . . . . . . . . . . . . . . . . . 49
14.2. Informative References . . . . . . . . . . . . . . . . . 49 13.7. Threat Analysis . . . . . . . . . . . . . . . . . . . . 49
Appendix A. Supporting v1 and v2 simultaneously . . . . . . . . 51 14. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 49
15. References . . . . . . . . . . . . . . . . . . . . . . . . . 49
15.1. Normative References . . . . . . . . . . . . . . . . . . 49
15.2. Informative References . . . . . . . . . . . . . . . . . 51
Appendix A. Supporting v1 and v2 simultaneously . . . . . . . . 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, but in this misissuance. Note that this is a general mechanism; but in this
document, we only describe its use for public TLS server certificates document, we only describe its use for public TLS server certificates
issued by public certification authorities (CAs). issued by public certification authorities (CAs).
Each log consists of certificate chains, which can be submitted by Each log contains certificate chains, which can be submitted by
anyone. It is expected that public CAs will contribute all their anyone. It is expected that public CAs will contribute all their
newly issued certificates to one or more logs, however certificate newly issued certificates to one or more logs; however certificate
holders can also contribute their own certificate chains, as can holders can also contribute their own certificate chains, as can
third parties. In order to avoid logs being rendered useless by the third parties. In order to avoid logs being rendered useless by the
submission of large numbers of spurious certificates, it is required submission of large numbers of spurious certificates, it is required
that each chain ends with a trust anchor that is accepted by the log. that each chain ends with a trust anchor that is accepted by the log.
When a chain is accepted by a log, a signed timestamp is returned, When a chain is accepted by a log, a signed timestamp is returned,
which can later be used to provide evidence to TLS clients that the which can later be used to provide evidence to TLS clients that the
chain has been submitted. TLS clients can thus require that all chain has been submitted. TLS clients can thus require that all
certificates they accept as valid are accompanied by signed certificates they accept as valid are accompanied by signed
timestamps. timestamps.
Those who are concerned about misissuance can monitor the logs, Those who are concerned about misissuance can monitor the logs,
asking them regularly for all new entries, and can thus check whether asking them regularly for all new entries, and can thus check whether
domains they are responsible for have had certificates issued that domains for which they are responsible have had certificates issued
they did not expect. What they do with this information, that they did not expect. What they do with this information,
particularly when they find that a misissuance has happened, is particularly when they find that a misissuance has happened, is
beyond the scope of this document, but broadly speaking, they can beyond the scope of this document; but, broadly speaking, they can
invoke existing business mechanisms for dealing with misissued invoke existing business mechanisms for dealing with misissued
certificates, such as working with the CA to get the certificate certificates, such as working with the CA to get the certificate
revoked, or with maintainers of trust anchor lists to get the CA revoked, or with maintainers of trust anchor lists to get the CA
removed. Of course, anyone who wants can monitor the logs and, if removed. Of course, anyone who wants can monitor the logs and, if
they believe a certificate is incorrectly issued, take action as they they believe a certificate is incorrectly issued, take action as they
see fit. see fit.
Similarly, those who have seen signed timestamps from a particular Similarly, those who have seen signed timestamps from a particular
log can later demand a proof of inclusion from that log. If the log log can later demand a proof of inclusion from that log. If the log
is unable to provide this (or, indeed, if the corresponding is unable to provide this (or, indeed, if the corresponding
certificate is absent from monitors' copies of that log), that is certificate is absent from monitors' copies of that log), that is
evidence of the incorrect operation of the log. The checking evidence of the incorrect operation of the log. The checking
operation is asynchronous to allow clients to proceed without delay, operation is asynchronous to allow clients to proceed without delay,
despite possible issues such as network connectivity and the vagaries despite possible issues such as network connectivity and the vagaries
of firewalls. of firewalls.
The append-only property of each log is technically achieved using The append-only property of each log is achieved using Merkle Trees,
Merkle Trees, which can be used to show that any particular instance which can be used to show that any particular instance of the log is
of the log is a superset of any particular previous instance. a superset of any particular previous instance. Likewise, Merkle
Likewise, Merkle Trees avoid the need to blindly trust logs: if a log Trees avoid the need to blindly trust logs: if a log attempts to show
attempts to show different things to different people, this can be different things to different people, this can be efficiently
efficiently detected by comparing tree roots and consistency proofs. detected by comparing tree roots and consistency proofs. Similarly,
Similarly, other misbehaviors of any log (e.g., issuing signed other misbehaviors of any log (e.g., issuing signed timestamps for
timestamps for certificates they then don't log) can be efficiently certificates they then don't log) can be efficiently detected and
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 RFC 2119 [RFC2119].
1.2. Data Structures 1.2. Data Structures
Data structures are defined according to the conventions laid out in Data structures are defined according to the conventions laid out in
Section 4 of [RFC5246]. Section 4 of [RFC5246].
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 Logs use a binary Merkle Hash Tree for efficient auditing. The
hashing algorithm used by each log is expected to be specified as hashing algorithm used by each log is expected to be specified as
part of the metadata relating to that log. We have established a part of the metadata relating to that log (see Section 10.1). We
registry of acceptable algorithms, see Section 11.2. The hashing have established a registry of acceptable algorithms, see
algorithm in use is referred to as HASH throughout this document and Section 12.2. The hashing algorithm in use is referred to as HASH
the size of its output in bytes as HASH_SIZE. The input to the throughout this document and the size of its output in bytes as
Merkle Tree Hash is a list of data entries; these entries will be HASH_SIZE. The input to the Merkle Tree Hash is a list of data
hashed to form the leaves of the Merkle Hash Tree. The output is a entries; these entries will be hashed to form the leaves of the
single HASH_SIZE Merkle Tree Hash. Given an ordered list of n Merkle Hash Tree. The output is a single HASH_SIZE Merkle Tree Hash.
inputs, D[n] = {d(0), d(1), ..., d(n-1)}, the Merkle Tree Hash (MTH) Given an ordered list of n inputs, D[n] = {d(0), d(1), ..., d(n-1)},
is thus defined as follows: 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
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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), ..., Given an ordered list of n inputs to the tree, D[n] = {d(0), ...,
d(n-1)}, the Merkle inclusion proof PATH(m, D[n]) for the (m+1)th 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: 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 where : is concatenation of lists and D[k1:k2] denotes the length (k2
- k1) list {d(k1), d(k1+1),..., d(k2-1)} as before. - k1) list {d(k1), d(k1+1),..., d(k2-1)} as before.
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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
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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 2.1.4. Signatures
Various data structures are signed. A log MUST use one of the Various data structures are signed. A log MUST use one of the
signature algorithms defined in the Section 11.3. signature algorithms defined in the Section 12.3.
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 5.6). The submitter SHOULD validate the Timestamp (SCT) (see Section 5.6). The submitter SHOULD validate the
returned SCT as described in Section 9.2 if they understand its returned SCT as described in Section 10.2 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 6.1) to a log. Since Any entity can submit a certificate (Section 6.1) to a log. Since
certificates may not be accepted by TLS clients unless logged, it is certificates may not be accepted by TLS clients unless logged, it is
expected that certificate owners or their CAs will usually submit expected that certificate owners or their CAs will usually submit
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Alternatively, (root as well as intermediate) CAs may preannounce a Alternatively, (root as well as intermediate) CAs may preannounce a
certificate prior to issuance by submitting a precertificate certificate prior to issuance by submitting a precertificate
(Section 6.2) that the log can use to create an entry that will be (Section 6.2) that the log can use to create an entry that will be
valid against the issued certificate. The CA MAY incorporate the valid against the issued certificate. The CA MAY incorporate the
returned SCT in the issued certificate. Examples of situations where returned SCT in the issued certificate. Examples of situations where
the returned SCT is not incorporated into the issued certificate the returned SCT is not incorporated into the issued certificate
would be when a CA sends the precertificate to multiple logs, but would be when a CA sends the precertificate to multiple logs, but
only incorporates the SCTs that are returned first, or the CA is only incorporates the SCTs that are returned first, or the CA is
using domain name redaction (Section 4.2) and intends to use another using domain name redaction (Section 4.2) and intends to use another
mechanism to publish SCTs (such as an OCSP response (Section 8.1.1) mechanism to publish SCTs (such as an OCSP response (Section 9.1.1)
or the TLS extension (Section 7.5)). or the TLS extension (Section 8.5)).
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 requirements:
o It MUST be DER encoded. o It MUST be DER encoded.
o "SignedData.encapContentInfo.eContentType" MUST be the OID o "SignedData.encapContentInfo.eContentType" MUST be the OID
1.3.101.78. 1.3.101.78.
o "SignedData.encapContentInfo.eContent" MUST contain a o "SignedData.encapContentInfo.eContent" MUST contain a
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precertificate could contain "*.?.?.example.com" instead, but not precertificate could contain "*.?.?.example.com" instead, but not
"?.?.?.example.com" instead. "?.?.?.example.com" instead.
4.2.2. Redacted Labels Certificate Extension 4.2.2. Redacted Labels Certificate Extension
When a precertificate contains one or more "?" labels, a non-critical When a precertificate contains one or more "?" labels, a non-critical
extension (OID 1.3.101.77, whose extnValue OCTET STRING contains an extension (OID 1.3.101.77, whose extnValue OCTET STRING contains an
ASN.1 SEQUENCE OF INTEGERs) MUST be added to the corresponding ASN.1 SEQUENCE OF INTEGERs) MUST be added to the corresponding
certificate. The purpose of this extension is to enable TLS clients certificate. The purpose of this extension is to enable TLS clients
to reconstruct the TBSCertificate component of the precertificate to reconstruct the TBSCertificate component of the precertificate
from the certificate, as described in Section 9.2.2. from the certificate, as described in Section 10.2.2.
Each INTEGER MUST have a value of zero or more. The first INTEGER Each INTEGER MUST have a value of zero or more. The first INTEGER
indicates the total number of "?" labels in the precertificate's indicates the total number of "?" labels in the precertificate's
first DNS-ID; the second INTEGER does the same for the first DNS-ID; the second INTEGER does the same for the
precertificate's second DNS-ID; etc. The last INTEGER does the same precertificate's second DNS-ID; etc. The last INTEGER does the same
for the precertificate's zero or more CN-IDs. There MUST NOT be more for the precertificate's zero or more CN-IDs. There MUST NOT be more
INTEGERs than there are DNS-IDs (plus one, if any CN-IDs are INTEGERs than there are DNS-IDs (plus one, if any CN-IDs are
present); if there are fewer INTEGERs than this, the shortfall is present); if there are fewer INTEGERs than this, the shortfall is
made up by implicitly repeating the last INTEGER. made up by implicitly repeating the last INTEGER.
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5. Log Format and Operation 5. 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 a valid submission, the log MUST return an SCT that When it receives a valid submission, the log MUST return an SCT that
corresponds to the submitted certificate or precertificate. If the corresponds to the submitted certificate or precertificate. If the
log has previously seen this valid submission, it SHOULD return the log has previously seen this valid submission, it SHOULD return the
same SCT as it returned before (to reduce the ability to track same SCT as it returned before (to reduce the ability to track
clients as described in Section 12.5). Note that if a certificate clients as described in Section 13.5). If different SCTs are
was previously logged as a precertificate, then the precertificate's produced for the same submission, multiple log entries will have to
SCT of type "precert_sct_v2" would not be appropriate; instead, a be created, one for each SCT (as the timestamp is a part of the leaf
fresh SCT of type "x509_sct_v2" should be generated. structure). Note that if a certificate was previously logged as a
precertificate, then the precertificate's SCT of type
"precert_sct_v2" would not be appropriate; instead, a fresh 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 incorporate the submitted entry in its
Merkle Tree no later than a fixed amount of time, known as the Merkle Tree no later than a fixed amount of time, known as the
Maximum Merge Delay (MMD), after the issuance of the SCT. Maximum Merge Delay (MMD), after the issuance of the SCT.
Periodically, the log MUST append all its new entries to its Merkle Periodically, the log MUST append all its new entries to its Merkle
Tree and sign the root of the tree. Tree and sign the root of the tree.
Log operators MUST NOT impose any conditions on retrieving or sharing Log operators MUST NOT impose any conditions on retrieving or sharing
data from the log. data from the log.
5.1. Accepting Submissions 5.1. Accepting Submissions
Logs MUST verify that each submitted certificate or precertificate Logs MUST verify that each submitted certificate or precertificate
has a valid signature chain to an accepted trust anchor, using the has a valid signature chain to an accepted trust anchor, using the
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verification rules in order to accommodate quirks of CA certificate- verification rules in order to accommodate quirks of CA certificate-
issuing software. However, logs MUST reject submissions without a issuing software. However, logs MUST reject submissions without a
valid signature chain to an accepted trust anchor. Logs MUST also valid signature chain to an accepted trust anchor. Logs MUST also
reject precertificates that do not conform to the requirements in reject precertificates that do not conform to the requirements in
Section 3.2. 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 specified in the log's metadata.
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 6.8), each of which is a root or intermediate CA (see Section 6.9), 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.
5.2. Log Entries 5.2. 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
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"precertificate_chain" is a vector of 1 or more additional "precertificate_chain" is a vector of 1 or more additional
certificates required to verify "pre_certificate". The first certificates required to verify "pre_certificate". The first
certificate MUST certify "pre_certificate". Each following certificate MUST certify "pre_certificate". Each following
certificate MUST directly certify the one preceding it. The final certificate MUST directly certify the one preceding it. The final
certificate MUST be a trust anchor accepted by the log. certificate MUST be a trust anchor accepted by the log.
5.3. Log ID 5.3. Log ID
Each log is uniquely identified by an OID. A log's operator MUST Each log is uniquely identified by an OID. A log's operator MUST
either allocate the OID themselves or request an OID from one of the either allocate the OID themselves or request an OID from one of the
two Log ID Registries (see Section 11.6.1 and Section 11.6.2). The two Log ID Registries (see Section 12.6.1 and Section 12.6.2). The
OID is specified in the log's metadata. Various data structures OID is specified in the log's metadata. Various data structures
include the DER encoding of this OID, excluding the ASN.1 tag and include the DER encoding of this OID, excluding the ASN.1 tag and
length bytes, in an opaque vector: 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.
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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". "tbs_certificate".
"tbs_certificate" is the DER encoded TBSCertificate from either the "tbs_certificate" is the DER encoded TBSCertificate from either the
"leaf_certificate" (in the case of an "X509ChainEntry") or the "leaf_certificate" (in the case of an "X509ChainEntry") or the
"pre_certificate" (in the case of a "PrecertChainEntryV2"). (Note "pre_certificate" (in the case of a "PrecertChainEntryV2"). (Note
that a precertificate's TBSCertificate can be reconstructed from the that a precertificate's TBSCertificate can be reconstructed from the
corresponding certificate as described in Section 9.2.2). corresponding certificate as described in Section 10.2.2).
"sct_extensions" matches the SCT extensions of the corresponding SCT. "sct_extensions" matches the SCT extensions of the corresponding SCT.
5.6. Signed Certificate Timestamp (SCT) 5.6. 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 { enum {
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} 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 5.3. described in Section 5.3.
"timestamp" is equal to the timestamp from the "timestamp" is equal to the timestamp from the
"TimestampedCertificateEntryDataV2" structure encapsulated in the "TimestampedCertificateEntryDataV2" structure encapsulated in the
"timestamped_entry". "timestamped_entry".
"sct_extension_type" identifies a single extension from the IANA "sct_extension_type" identifies a single extension from the IANA
registry in Section 11.4. At the time of writing, no extensions are registry in Section 12.4. At the time of writing, no extensions are
specified. specified.
The interpretation of the "sct_extension_data" field is determined The interpretation of the "sct_extension_data" field is determined
solely by the value of the "sct_extension_type" field. Each document solely by the value of the "sct_extension_type" field. Each document
that registers a new "sct_extension_type" must describe how to that registers a new "sct_extension_type" must describe how to
interpret the corresponding "sct_extension_data". 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 "sct_extension_type". The extensions in the vector MUST be ordered
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Each subsequent timestamp MUST be more recent than the timestamp of Each subsequent timestamp MUST be more recent than the timestamp of
the previous update. the previous update.
"tree_size" is equal to the tree size from the "TreeHeadDataV2" "tree_size" is equal to the tree size from the "TreeHeadDataV2"
structure encapsulated in "merkle_tree_head". structure encapsulated in "merkle_tree_head".
"root_hash" is equal to the root hash from the "TreeHeadDataV2" "root_hash" is equal to the root hash from the "TreeHeadDataV2"
structure encapsulated in "merkle_tree_head". structure encapsulated in "merkle_tree_head".
"sth_extension_type" identifies a single extension from the IANA "sth_extension_type" identifies a single extension from the IANA
registry in Section 11.5. At the time of writing, no extensions are registry in Section 12.5. At the time of writing, no extensions are
specified. specified.
The interpretation of the "sth_extension_data" field is determined The interpretation of the "sth_extension_data" field is determined
solely by the value of the "sth_extension_type" field. Each document solely by the value of the "sth_extension_type" field. Each document
that registers a new "sth_extension_type" must describe how to that registers a new "sth_extension_type" must describe how to
interpret the corresponding "sth_extension_data". interpret the corresponding "sth_extension_data".
"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 "sth_extension_type". The extensions in the vector MUST be ordered
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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. Some codes are
generic and are detailed here. Others are detailed in the generic and are detailed here. Others are detailed in the
individual requests. Error codes are fixed text strings. individual requests. Error codes are fixed text strings.
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:
{ {
"error_message": "'start' cannot be greater than 'end'", "error_message": "'start' cannot be greater than 'end'",
"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
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shutdown The log has ceased operation and is not accepting new shutdown The log has ceased operation and is not accepting new
submissions. 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 MAY still log the certificate but SHOULD NOT correctly then the log MUST either log the certificate or return the
return an SCT. It should instead return the "bad certificate" error. "bad certificate" error. If the certificate is logged, an SCT MUST
Logging the certificate is useful, because monitors (Section 9.3) can be issued. Logging the certificate is useful, because monitors
then detect these encoding errors, which may be accepted by some TLS (Section 10.3) can then detect these encoding errors, which may be
clients. accepted by some TLS clients.
Note that not all certificate handling software is capable of
detecting all encoding errors (e.g. some software will accept BER
instead of DER encodings in certificates, or incorrect character
encodings, even though these are technically incorrect) .
6.2. Add PreCertChain to Log 6.2. Add PreCertChain to Log
POST https://<log server>/ct/v2/add-pre-chain POST https://<log server>/ct/v2/add-pre-chain
Inputs: Inputs:
precertificate: The base64 encoded precertificate. precertificate: The base64 encoded precertificate.
chain: An array of base64 encoded CA certificates. The first chain: An array of base64 encoded CA certificates. The first
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signed. signed.
Error codes: Error codes:
first unknown "first" is before the latest known STH but is not first unknown "first" is before the latest known STH but is not
from an existing STH. from an existing STH.
second unknown "second" is before the latest known STH but is not second unknown "second" is before the latest known STH but is not
from an existing STH. from an existing STH.
See Section 9.4.2 for an outline of how to use the "consistency" See Section 10.4.2 for an outline of how to use the "consistency"
output. output.
6.5. Retrieve Merkle Inclusion Proof from Log by Leaf Hash 6.5. 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.
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signed. signed.
Error codes: Error codes:
hash unknown "hash" is not the hash of a known leaf (may be hash unknown "hash" is not the hash of a known leaf (may be
caused by skew or by a known certificate not yet merged). caused by skew or by a known certificate not yet merged).
tree_size unknown "hash" is before the latest known STH but is tree_size unknown "hash" is before the latest known STH but is
not from an existing STH. not from an existing STH.
See Section 9.4.1 for an outline of how to use the "inclusion" See Section 10.4.1 for an outline of how to use the "inclusion"
output. output.
6.6. Retrieve Merkle Inclusion Proof, Signed Tree Head and Consistency 6.6. 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.
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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 6.5. Errors are the same as in Section 6.5.
See Section 9.4.1 for an outline of how to use the "inclusion" See Section 10.4.1 for an outline of how to use the "inclusion"
output, and see Section 9.4.2 for an outline of how to use the output, and see Section 10.4.2 for an outline of how to use the
"consistency" output. "consistency" output.
6.7. Retrieve Entries and STH from Log 6.7. 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.
skipping to change at page 29, line 37 skipping to change at page 30, line 19
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 leaf_input: The base64 encoded "TransItem" structure of type
"x509_entry_v2" or "precert_entry_v2" (see Section 5.5). "x509_entry_v2" or "precert_entry_v2" (see Section 5.5).
log_entry: The base64 encoded log entry (see Section 5.2). In log_entry: The base64 encoded log entry (see Section 5.2). In
the case of an "x509_entry_v2" entry, this is the whole the case of an "x509_entry_v2" entry, this is the whole
"X509ChainEntry"; and in the case of a "precert_entry_v2", "X509ChainEntry"; and in the case of a "precert_entry_v2",
this is the whole "PrecertChainEntryV2". this is the whole "PrecertChainEntryV2".
sct: A 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. Note that "precert_sct_v2" corresponding to this log entry.
more than one SCT may have been returned for the same entry
- only one of those is returned in this field. It may not
be possible to retrieve others.
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
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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 9.4.3 for an outline of how to use a complete list of See Section 10.4.3 for an outline of how to use a complete list of
"leaf_input" entries to verify the "root_hash". "leaf_input" entries to verify the "root_hash".
6.8. Retrieve Accepted Trust Anchors 6.8. Get Entry Number for SCT
GET https://<log server>/ct/v2/get-entry-for-sct
Inputs:
sct: A base64 encoded "TransItem" of type "x509_sct_v2" or
"precert_sct_v2" allegedly from this log.
Outputs:
entry: 0-based index of the log entry corresponding to the
supplied SCT.
Error codes:
bad signature "sct" is not signed by this log.
not found "sct" does not correspond to an entry that is currently
available.
Note that any SCT with a valid signature MUST have a corresponding
entry in the log, but it may not be retrievable until the MMD has
passed since the SCT was issued.
6.9. 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: If the server has chosen to limit the length of chains
it accepts, this is the maximum number of certificates in the it accepts, this is the maximum number of certificates in the
chain, in decimal. If there is no limit, this is omitted. chain, in decimal. If there is no limit, this is omitted.
7. TLS Servers 7. Optional Client Messages
Logs MAY implement these messages. They are not required for correct
operation of logs or their clients, but may be convenient in some
circumstances. Note that mirrors can implement these even if the log
they are mirroring does not.
7.1. Get Entry Number for SCT
GET https://<log server>/ct/v2/get-entry-for-sct
Inputs:
sct: A base64 encoded "TransItem" of type "x509_sct_v2" or
"precert_sct_v2" signed by this log.
Outputs:
entry: 0-based index of the log entry corresponding to the
supplied SCT.
Error codes:
bad signature "sct" is not signed by this log.
not found "sct" does not correspond to an entry that is currently
available.
Note that any SCT signed by a log MUST have a corresponding entry in
the log, but it may not be retrievable until the MMD has passed since
the SCT was issued.
7.2. Get Entry Numbers for Certificate
GET https://<log server>/ct/v2/get-entry-for-certificate
Inputs:
hash: A base64 encoded HASH of a "TBSCertificate". Note that if
the certificate has redacted labels then the "TBSCertificate"
must be constructed as described above (Section 4.2).
Outputs:
entries: An array of 0-based indices of log entries corresponding
to the supplied HASH.
Error codes:
bad hash "hash" is not the right size or format.
not found "sct" does not correspond to an entry that is currently
available.
Note that it is possible for a certificate to be logged more than
once. If that is the case, the log MAY return more than one entry
index. If the certificate is present in the log, then the log MUST
return at least one entry index.
8. 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 or to a name-constrained intermediate the server server certificate or to a name-constrained intermediate the server
certificate chains to. TLS servers SHOULD also present corresponding certificate chains to. TLS servers SHOULD also present corresponding
inclusion proofs and STHs (see Section 7.3). inclusion proofs and STHs (see Section 8.3).
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 7.5). This mechanism allows TLS "transparency_info" (see Section 8.5). 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 8.1.1), where the OCSP response is provided extension (see Section 9.1.1), 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)
implemented. It also allows SCTs and inclusion proofs to be implemented. It also allows SCTs and inclusion proofs to be
updated on the fly. updated on the fly.
o An X509v3 certificate extension (see Section 8.1.2). This o An X509v3 certificate extension (see Section 9.1.2). This
mechanism allows the use of unmodified TLS servers, but the SCTs mechanism allows the use of unmodified TLS servers, but the SCTs
and inclusion proofs cannot be updated on the fly. Since the logs and inclusion proofs cannot be updated on the fly. Since the logs
from where the SCTs and inclusion proofs originated won't from where the SCTs and inclusion proofs originated won't
necessarily be accepted by TLS clients for the full lifetime of necessarily be accepted by TLS clients for the full lifetime of
the certificate, there is a risk that TLS clients will the certificate, there is a risk that TLS clients will
subsequently consider the certificate to be non-compliant and in subsequently consider the certificate to be non-compliant and in
need of re-issuance. need of re-issuance.
Additionally, a TLS server which supports presenting SCTs using an Additionally, a TLS server which supports presenting SCTs using an
OCSP response MAY provide it when the TLS client included the OCSP response MAY provide it when the TLS client included the
"status_request_v2" extension ([RFC6961]) in the (extended) "status_request_v2" extension ([RFC6961]) in the (extended)
"ClientHello", but only in addition to at least one of the three "ClientHello", but only in addition to at least one of the three
mechanisms listed above. mechanisms listed above.
7.1. Multiple SCTs 8.1. Multiple SCTs
TLS servers SHOULD send SCTs from multiple logs in case one or more TLS servers SHOULD send SCTs from multiple logs in case one or more
logs are not acceptable to the TLS client (for example, if a log has logs are not acceptable to the TLS client (for example, if a log has
been struck off for misbehavior, has had a key compromise, or is not been struck off for misbehavior, has had a key compromise, or is not
known to the TLS client). For example: known to the TLS client). For example:
o If a CA and a log collude, it is possible to temporarily hide o If a CA and a log collude, it is possible to temporarily hide
misissuance from clients. Including SCTs from different logs misissuance from clients. Including SCTs from different logs
makes it more difficult to mount this attack. makes it more difficult to mount this attack.
skipping to change at page 32, line 26 skipping to change at page 34, line 41
o TLS clients may have policies related to the above risks requiring o TLS clients may have policies related to the above risks requiring
servers to present multiple SCTs. For example, at the time of servers to present multiple SCTs. For example, at the time of
writing, Chromium [Chromium.Log.Policy] requires multiple SCTs to writing, Chromium [Chromium.Log.Policy] requires multiple SCTs to
be presented with EV certificates in order for the EV indicator to be presented with EV certificates in order for the EV indicator to
be shown. be shown.
To select the logs from which to obtain SCTs, a TLS server can, for To select the logs from which to obtain SCTs, a TLS server can, for
example, examine the set of logs popular TLS clients accept and example, examine the set of logs popular TLS clients accept and
recognize. recognize.
7.2. TransItemList Structure 8.2. TransItemList Structure
Multiple SCTs, inclusion proofs, and indeed "TransItem" structures of Multiple SCTs, inclusion proofs, and indeed "TransItem" structures of
any type, are combined into a list as follows: any type, are combined into a list as follows:
opaque SerializedTransItem<1..2^16-1>; opaque SerializedTransItem<1..2^16-1>;
struct { struct {
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).
7.3. Presenting SCTs, inclusion proofs and STHs 8.3. Presenting SCTs, inclusion proofs and STHs
When constructing a "TransItemList" structure, a TLS server SHOULD When constructing a "TransItemList" structure, a TLS server SHOULD
construct and include "TransItem" structures of type construct and include "TransItem" structures of type
"x509_sct_with_proof_v2" (for an SCT of type "x509_sct_v2") or "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"), "precert_sct_with_proof_v2" (for an SCT of type "precert_sct_v2"),
both of which encapsulate a "SCTWithProofDataV2" structure: both of which encapsulate a "SCTWithProofDataV2" structure:
struct { struct {
SignedCertificateTimestampDataV2 sct; SignedCertificateTimestampDataV2 sct;
SignedTreeHeadDataV2 sth; SignedTreeHeadDataV2 sth;
InclusionProofDataV2 inclusion_proof; InclusionProofDataV2 inclusion_proof;
skipping to change at page 33, line 27 skipping to change at page 35, line 37
to the server certificate or to a name-constrained intermediate the to the server certificate or to a name-constrained intermediate the
server certificate chains to. server certificate chains to.
"sth" is the encapsulated data structure from an STH that was signed "sth" is the encapsulated data structure from an STH that was signed
by the same log as "sct". by the same log as "sct".
"inclusion_proof" is the encapsulated data structure from an "inclusion_proof" is the encapsulated data structure from an
inclusion proof that corresponds to "sct" and can be used to compute inclusion proof that corresponds to "sct" and can be used to compute
the root in "sth". the root in "sth".
7.4. Presenting SCTs only 8.4. Presenting SCTs only
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 9.2.4) and reduces load on protect the client's privacy (see Section 10.2.4) and reduces load on
log servers. However, if a TLS server is unable to obtain an log servers. However, if a TLS server is unable to obtain an
inclusion proof and STH that correspond to an SCT, then it MUST inclusion proof and STH that correspond to an SCT, then it MUST
include "TransItem" structures of type "x509_sct_v2" or include "TransItem" structures of type "x509_sct_v2" or
"precert_sct_v2" in the "TransItemList". "precert_sct_v2" in the "TransItemList".
7.5. transparency_info TLS Extension 8.5. 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.
8. Certification Authorities 9. Certification Authorities
8.1. Transparency Information X.509v3 Extension
9.1. 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 8.1.1) and certificates (see included in OCSP responses (see Section 9.1.1) and certificates (see
Section 8.1.2). Since RFC5280 requires the "extnValue" field (an Section 9.1.2). 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
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".
8.1.1. OCSP Response Extension 9.1.1. 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. The included SCTs or 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 or for a precertificate that corresponds to that certificate, or for
a name-constrained intermediate to which that certificate chains. a name-constrained intermediate to which that certificate chains.
8.1.2. Certificate Extension 9.1.2. 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. Any included SCTs or inclusion
proofs MUST be either for a precertificate that corresponds to this proofs MUST be either for a precertificate that corresponds to this
certificate, or for a name-constrained intermediate to which this certificate, or for a name-constrained intermediate to which this
certificate chains. certificate chains.
8.2. TLS Feature Extension 9.2. TLS Feature Extension
A certification authority MAY include the transparency_info A certification authority MAY include the transparency_info
(Section 7.5) TLS extension identifier in the TLS Feature [RFC7633] (Section 8.5) TLS extension identifier in the TLS Feature [RFC7633]
certificate extension in root, intermediate and end-entity certificate extension in root, intermediate and end-entity
certificates. When a certificate chain includes such a certificate, certificates. When a certificate chain includes such a certificate,
this indicates that CT compliance is required. this indicates that CT compliance is required.
9. Clients 10. 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 metadata in order to communicate with logs
and verify their responses. This metadata is described below, but and verify their responses. This metadata is described below, but
note that this document does not describe how the metadata is note that this document does not describe how the metadata is
obtained, which is implementation dependent (see, for example, obtained, which is implementation dependent (see, for example,
[Chromium.Policy]). [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.
9.1. Metadata 10.1. Metadata
In order to communicate with and verify a log, clients need metadata In order to communicate with and verify a log, clients need metadata
about the log. about the log.
Base URL: The URL to substitute for <log server> in Section 6. Base URL: The URL to substitute for <log server> in Section 6.
Hash Algorithm The hash algorithm used for the Merkle Tree (see Hash Algorithm The hash algorithm used for the Merkle Tree (see
Section 11.2). Section 12.2).
Signing Algorithm The signing algorithm used (see Section 2.1.4). Signing Algorithm The signing algorithm used (see Section 2.1.4).
Public Key The public key used to verify signatures generated by the 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. A log MUST NOT use the same keypair as any other log.
Log ID The OID that uniquely identifies the log. Log ID The OID that uniquely identifies the log.
Maximum Merge Delay The MMD the log has committed to. Maximum Merge Delay The MMD the log has committed to.
skipping to change at page 36, line 5 skipping to change at page 38, line 13
Section 5.8). Section 5.8).
Final STH If a log has been closed down (i.e. no longer accepts new 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 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 client should know the final valid STH in the log to ensure no new
entries can be added without detection. entries can be added without detection.
[JSON.Metadata] is an example of a metadata format which includes the [JSON.Metadata] is an example of a metadata format which includes the
above elements. above elements.
9.2. TLS Client 10.2. TLS Client
9.2.1. Receiving SCTs 10.2.1. Receiving SCTs
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 7). TLS clients MAY also accept SCTs via present SCTs (see Section 8). 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.
9.2.2. Reconstructing the TBSCertificate 10.2.2. 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: a certificate, TLS clients should:
o Remove the Redacted Labels extension described in Section 4.2.2 o Remove the Redacted Labels extension described in Section 4.2.2
o Replace leftmost labels of each DNS-ID with "?", based on the o Replace leftmost labels of each DNS-ID with "?", based on the
INTEGER value corresponding to that DNS-ID in the extension. INTEGER value corresponding to that DNS-ID in the extension.
A certificate with redacted labels where one of the redacted labels A certificate with redacted labels where one of the redacted labels
is "*" MUST NOT be considered compliant. is "*" MUST NOT be considered compliant.
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).
9.2.3. Validating SCTs 10.2.3. 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 metadata. To validate an SCT, a TLS
client computes the signature input from the SCT data and the client computes the signature input from the SCT data and the
corresponding certificate, and then verifies the signature using the corresponding certificate, and then verifies the signature using the
corresponding log's public key. TLS clients MUST NOT consider valid corresponding log's public key. TLS clients MUST NOT consider valid
any SCT whose timestamp is in the future. any SCT whose timestamp is in the future.
Before considering any SCT to be invalid, the TLS client MUST attempt Before considering any SCT to be invalid, the TLS client MUST attempt
to validate it against the server certificate and against each of the to validate it against the server certificate and against each of the
zero or more suitable name-constrained intermediates (Section 4.3) in zero or more suitable name-constrained intermediates (Section 4.3) in
the chain. These certificates may be evaluated in the order they the chain. These certificates may be evaluated in the order they
appear in the chain, or, indeed, in any order. appear in the chain, or, indeed, in any order.
9.2.4. Validating inclusion proofs 10.2.4. Validating inclusion proofs
After validating a received SCT, a TLS client MAY request a After validating a received SCT, a TLS client MAY request a
corresponding inclusion proof (if one is not already available) and corresponding inclusion proof (if one is not already available) and
then verify it. An inclusion proof can be requested directly from a then verify it. An inclusion proof can be requested directly from a
log using "get-proof-by-hash" (Section 6.5) or "get-all-by-hash" log using "get-proof-by-hash" (Section 6.5) or "get-all-by-hash"
(Section 6.6), but note that this will disclose to the log which TLS (Section 6.6), but note that this will disclose to the log which TLS
server the client has been communicating with. server the client has been communicating with.
Alternatively, if the TLS client has received an inclusion proof (and Alternatively, if the TLS client has received an inclusion proof (and
an STH) alongside the SCT, it can proceed to verifying the inclusion an STH) alongside the SCT, it can proceed to verifying the inclusion
proof to the provided STH. The client then has to verify consistency 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 between the provided STH and an STH it knows about, which is less
sensitive from a privacy perspective. sensitive from a privacy perspective.
TLS clients SHOULD also verify each received inclusion proof (see TLS clients SHOULD also verify each received inclusion proof (see
Section 9.4.1) for which they have the corresponding log's metadata, Section 10.4.1) for which they have the corresponding log's metadata,
to audit the log and gain confidence that the certificate is logged. to audit the log and gain confidence that the certificate is logged.
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 6.3), process of auditing, request a new STH from the log (Section 6.3),
then verify it by requesting a consistency proof (Section 6.4). Note then verify it by requesting a consistency proof (Section 6.4). 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.
9.2.5. Evaluating compliance 10.2.5. Evaluating compliance
To be considered compliant, a certificate MUST be accompanied by at To be considered compliant, a certificate MUST be accompanied by at
least one valid SCT. A certificate not accompanied by any valid SCTs least one valid SCT. A certificate not accompanied by any valid SCTs
MUST NOT be considered compliant by TLS clients. MUST NOT be considered compliant by TLS clients.
9.2.6. TLS Feature Extension 10.2.6. TLS Feature Extension
If any certificate in a chain includes the transparency_info If any certificate in a chain includes the transparency_info
(Section 7.5) TLS extension identifier in the TLS Feature [RFC7633] (Section 8.5) TLS extension identifier in the TLS Feature [RFC7633]
certificate extension, then CT compliance (using any of the certificate extension, then CT compliance (using any of the
mechanisms from Section 7) is required. mechanisms from Section 8) is required.
TLS clients MUST treat certificates which fail this requirement as TLS clients MUST treat certificates which fail this requirement as
non-compliant. non-compliant.
9.2.7. Handling of Non-compliance 10.2.7. Handling of Non-compliance
If a TLS server presents a certificate chain that is non-compliant, If a TLS server presents a certificate chain that is non-compliant,
there are two possibilities. there are two possibilities.
o In the case that use of TLS with a valid certificate is mandated o In the case that use of TLS with a valid certificate is mandated
by explicit security policy, application protocol specification, by explicit security policy, application protocol specification,
or other means, the TLS client MUST refuse the connection. or other means, the TLS client MUST refuse the connection.
o If the use of TLS with a valid certificate is optional, the TLS o If the use of TLS with a valid certificate is optional, the TLS
client MAY accept the connection but MUST NOT treat the client MAY accept the connection but MUST NOT treat the
certificate as valid. certificate as valid.
9.3. Monitor 10.3. 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:
skipping to change at page 39, line 12 skipping to change at page 41, line 20
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 6.4). STH (Section 6.4).
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.
9.4. Auditing 10.4. 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 behaviour properties that should be
checked: checked:
o The Maximum Merge Delay (MMD). o The Maximum Merge Delay (MMD).
skipping to change at page 39, line 41 skipping to change at page 41, line 49
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 9.3) can audit by verifying the consistency of A monitor (Section 10.3) 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 9.2) can audit by verifying an SCT against any A TLS client (Section 10.2) 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 6.5). It can also requesting a Merkle inclusion proof (Section 6.5). It can also
verify that the SCT corresponds to the certificate it arrived with verify that the SCT corresponds to the certificate it arrived with
(i.e. the log entry is that certificate, is a precertificate for that (i.e. the log entry is that certificate, is a precertificate for that
certificate or is an appropriate name-constrained intermediate [see certificate or is an appropriate name-constrained intermediate [see
Section 4.3]). Section 4.3]).
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 12.4. Section 13.4.
The following algorithm outlines may be useful for clients that wish The following algorithm outlines may be useful for clients that wish
to perform various audit operations. to perform various audit operations.
9.4.1. Verifying an inclusion proof 10.4.1. Verifying an inclusion proof
When a client has received a "TransItem" of type "inclusion_proof_v2" 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 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 given "tree_size" and "root_hash", the following algorithm may be
used to prove the "hash" was included in the "root_hash": used to prove the "hash" was included in the "root_hash":
1. Compare "leaf_index" against "tree_size". If "leaf_index" is 1. Compare "leaf_index" against "tree_size". If "leaf_index" is
greater than or equal to "tree_size" fail the proof verification. greater than or equal to "tree_size" fail the proof verification.
2. Set "fn" to "leaf_index" and "sn" to "tree_size - 1". 2. Set "fn" to "leaf_index" and "sn" to "tree_size - 1".
skipping to change at page 40, line 47 skipping to change at page 43, line 7
Set "r" to "HASH(0x01 || r || p)" Set "r" to "HASH(0x01 || r || p)"
Finally, right-shift both "fn" and "sn" one time. Finally, right-shift both "fn" and "sn" one time.
5. Compare "sn" to 0. Compare "r" against the "root_hash". If "sn" 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 is equal to 0, and "r" and the "root_hash" are equal, then the
log has proven the inclusion of "hash". Otherwise, fail the log has proven the inclusion of "hash". Otherwise, fail the
proof verification. proof verification.
9.4.2. Verifying consistency between two STHs 10.4.2. Verifying consistency between two STHs
When a client has an STH "first_hash" for tree size "first", an STH 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 "second_hash" for tree size "second" where "0 < first < second", and
has received a "TransItem" of type "consistency_proof_v2" that they has received a "TransItem" of type "consistency_proof_v2" that they
wish to use to verify both hashes, the following algorithm may be wish to use to verify both hashes, the following algorithm may be
used: used:
1. If "first" is an exact power of 2, then prepend "first_hash" to 1. If "first" is an exact power of 2, then prepend "first_hash" to
the "consistency_path" array. the "consistency_path" array.
skipping to change at page 41, line 41 skipping to change at page 44, line 5
Set "sr" to "HASH(0x01 || sr || c)" Set "sr" to "HASH(0x01 || sr || c)"
Finally, right-shift both "fn" and "sn" one time. Finally, right-shift both "fn" and "sn" one time.
6. After completing iterating through the "consistency_path" array 6. After completing iterating through the "consistency_path" array
as described above, verify that the "fr" calculated is equal to as described above, verify that the "fr" calculated is equal to
the "first_hash" supplied, that the "sr" calculated is equal to the "first_hash" supplied, that the "sr" calculated is equal to
the "second_hash" supplied and that "sn" is 0. the "second_hash" supplied and that "sn" is 0.
9.4.3. Verifying root hash given entries 10.4.3. Verifying root hash given entries
When a client has a complete list of leaf input "entries" from "0" up 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 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 "root_hash" returned by the log for the same "tree_size", the
following algorithm may be used: following algorithm may be used:
1. Set "stack" to an empty stack. 1. Set "stack" to an empty stack.
2. For each "i" from "0" up to "tree_size - 1": 2. For each "i" from "0" up to "tree_size - 1":
skipping to change at page 42, line 28 skipping to change at page 44, line 39
3. Push "HASH(0x01 || left || right)" to "stack". 3. Push "HASH(0x01 || left || right)" to "stack".
3. If there is more than one element in the "stack", repeat the same 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 merge procedure (Step 2.3 above) until only a single element
remains. remains.
4. The remaining element in "stack" is the Merkle Tree hash for the 4. The remaining element in "stack" is the Merkle Tree hash for the
given "tree_size" and should be compared by equality against the given "tree_size" and should be compared by equality against the
supplied "root_hash". supplied "root_hash".
10. Algorithm Agility 11. 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 9.1 live log, then the log should be frozen as specified in Section 10.1
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.
11. IANA Considerations 12. IANA Considerations
11.1. TLS Extension Type 12.1. TLS Extension Type
IANA is asked to allocate an RFC 5246 ExtensionType value for the IANA is asked to allocate an RFC 5246 ExtensionType value for the
"transparency_info" TLS extension. IANA should update this extension "transparency_info" TLS extension. IANA should update this extension
type to point at this document. type to point at this document.
11.2. Hash Algorithms 12.2. Hash Algorithms
IANA is asked to establish a registry of hash values, initially IANA is asked to establish a registry of hash values, initially
consisting of: consisting of:
+-------+----------------------+ +-------+----------------------+
| Index | Hash | | Index | Hash |
+-------+----------------------+ +-------+----------------------+
| 0 | SHA-256 [FIPS.180-4] | | 0 | SHA-256 [FIPS.180-4] |
+-------+----------------------+ +-------+----------------------+
11.3. Signature Algorithms 12.3. Signature Algorithms
IANA is asked to establish a registry of signature algorithm values, IANA is asked to establish a registry of signature algorithm values,
initially consisting of: initially consisting of:
+-------+-----------------------------------------------------------+ +-------+-----------------------------------------------------------+
| Index | Signature Algorithm | | Index | Signature Algorithm |
+-------+-----------------------------------------------------------+ +-------+-----------------------------------------------------------+
| 0 | deterministic ECDSA [RFC6979] using the NIST P-256 curve | | 0 | deterministic ECDSA [RFC6979] using the NIST P-256 curve |
| | (Section D.1.2.3 of the Digital Signature Standard [DSS]) | | | (Section D.1.2.3 of the Digital Signature Standard [DSS]) |
| | and HMAC-SHA256 | | | and HMAC-SHA256 |
| 1 | RSA signatures (RSASSA-PKCS1-v1_5 with SHA-256, Section | | 1 | RSA signatures (RSASSA-PKCS1-v1_5 with SHA-256, Section |
| | 8.2 of [RFC3447]) using a key of at least 2048 bits. | | | 8.2 of [RFC3447]) using a key of at least 2048 bits. |
+-------+-----------------------------------------------------------+ +-------+-----------------------------------------------------------+
11.4. SCT Extensions 12.4. SCT Extensions
IANA is asked to establish a registry of SCT extensions, initially IANA is asked to establish a registry of SCT extensions, initially
consisting of: consisting of:
+-------+-----------+ +-------+-----------+
| Type | Extension | | Type | Extension |
+-------+-----------+ +-------+-----------+
| 65535 | reserved | | 65535 | reserved |
+-------+-----------+ +-------+-----------+
TBD: policy for adding to the registry TBD: policy for adding to the registry
11.5. STH Extensions 12.5. STH Extensions
IANA is asked to establish a registry of STH extensions, initially IANA is asked to establish a registry of STH extensions, initially
consisting of: consisting of:
+-------+-----------+ +-------+-----------+
| Type | Extension | | Type | Extension |
+-------+-----------+ +-------+-----------+
| 65535 | reserved | | 65535 | reserved |
+-------+-----------+ +-------+-----------+
TBD: policy for adding to the registry TBD: policy for adding to the registry
11.6. Object Identifiers 12.6. 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 5.3), the precertificate CMS "eContentType" (see Section 5.3), 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 4.2.2, Section 4.3 and Section 8.1.2) and OCSP responses (see Section 4.2.2, Section 4.3 and Section 9.1.2) and OCSP responses (see
Section 8.1.1). The OIDs are defined in an arc that was selected due Section 9.1.1). The OIDs are defined in an arc that was selected due
to its short encoding. to its short encoding.
11.6.1. Log ID Registry 1 12.6.1. Log ID Registry 1
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.
IANA is requested to establish a registry that will allocate Log IDs IANA is requested to establish a registry that will allocate Log IDs
from this range. from this range.
TBD: policy for adding to the registry. Perhaps "Expert Review"? TBD: policy for adding to the registry. Perhaps "Expert Review"?
11.6.2. Log ID Registry 2 12.6.2. Log ID Registry 2
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.
IANA is requested to establish a registry that will allocate Log IDs IANA is requested to establish a registry that will allocate Log IDs
from this arc. from this arc.
TBD: policy for adding to the registry. Perhaps "Expert Review"? TBD: policy for adding to the registry. Perhaps "Expert Review"?
12. Security Considerations 13. 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
knows that a log has committed to publishing the certificate. From knows that a log has committed to publishing the certificate. From
this, the client knows that monitors acting for the subject of the this, the client knows that monitors acting for the subject of the
certificate have had some time to notice the misissue and take some certificate have had some time to notice the misissue and take some
action, such as asking a CA to revoke a misissued certificate, or action, such as asking a CA to revoke a misissued certificate, or
that the log has misbehaved, which will be discovered when the SCT is that the log has misbehaved, which will be discovered when the SCT is
audited. A signed timestamp is not a guarantee that the certificate audited. A signed timestamp is not a guarantee that the certificate
is not misissued, since appropriate monitors might not have checked is not misissued, since appropriate monitors might not have checked
the logs or the CA might have refused to revoke the certificate. the logs or the CA might have refused to revoke the certificate.
In addition, if TLS clients will not accept unlogged certificates, In addition, if TLS clients will not accept unlogged certificates,
then site owners will have a greater incentive to submit certificates then site owners will have a greater incentive to submit certificates
to logs, possibly with the assistance of their CA, increasing the to logs, possibly with the assistance of their CA, increasing the
overall transparency of the system. overall transparency of the system.
12.1. Misissued Certificates 13.1. 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 (so TLS clients do not have a valid SCT, are not considered compliant (so TLS clients
may decide, for example, to reject them). Misissued certificates may decide, for example, to reject them). Misissued certificates
that do have an SCT from a log will appear in that public log within that do have an SCT from a log will appear in that public log within
the Maximum Merge Delay, assuming the log is operating correctly. the Maximum Merge Delay, assuming the log is operating correctly.
Thus, the maximum period of time during which a misissued certificate Thus, the maximum period of time during which a misissued certificate
can be used without being available for audit is the MMD. can be used without being available for audit is the MMD.
12.2. Detection of Misissue 13.2. 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.
12.3. Avoiding Overly Redacting Domain Name Labels 13.3. Avoiding Overly Redacting Domain Name Labels
Redaction of domain name labels carries the same risks as the use of Redaction of domain name labels carries the same risks as the use of
wildcards (See Section 7.2 of [RFC6125], for example). If the wildcards (See Section 7.2 of [RFC6125], for example). If the
entirety of the domain space below the unredacted part of a domain entirety of the domain space below the unredacted part of a domain
name is not controlled by a single entity (e.g. "?.com", "?.co.uk" name is not controlled by a single entity (e.g. "?.com", "?.co.uk"
and other public suffixes [Public.Suffix.List]), then the domain name and other public suffixes [Public.Suffix.List]), then the domain name
may be considered by clients to be overly redacted. may be considered by clients to be overly redacted.
CAs should take care to avoid overly redacting domain names in CAs should take care to avoid overly redacting domain names in
precertificates. It is expected that monitors will treat precertificates. It is expected that monitors will treat
precertificates that contain overly redacted domain names as precertificates that contain overly redacted domain names as
potentially misissued. TLS clients MAY consider a certificate to be potentially misissued. TLS clients MAY consider a certificate to be
non-compliant if the reconstructed TBSCertificate (Section 9.2.2) non-compliant if the reconstructed TBSCertificate (Section 10.2.2)
contains any overly redacted domain names. contains any overly redacted domain names.
12.4. Misbehaving Logs 13.4. 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 the
[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
skipping to change at page 46, line 39 skipping to change at page 48, line 45
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). A proof
of misbehavior in such cases would be a series of STHs that were of misbehavior in such cases would be a series of STHs that were
issued too closely together, proving violation of the STH issuance issued too closely together, proving violation of the STH issuance
rate limit, or an STH with a root hash that does not match the one rate 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.
12.5. Deterministic Signatures 13.5. Deterministic Signatures
Logs are required to use deterministic signatures for the following Logs are required to use deterministic signatures for the following
reasons: reasons:
o Using non-deterministic ECDSA with a predictable source of o Using non-deterministic ECDSA with a predictable source of
randomness means that each signature can potentially expose the randomness means that each signature can potentially expose the
secret material of the signing key. secret material of the signing key.
o Clients that gossip STHs or report back SCTs can be tracked or o Clients that gossip STHs or report back SCTs can be tracked or
traced if a log was to produce multiple STHs or SCTs with the same traced if a log was to produce multiple STHs or SCTs with the same
timestamp and data but different signatures. timestamp and data but different signatures.
12.6. Multiple SCTs 13.6. 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 7.1). (see Section 8.1).
12.7. Threat Analysis 13.7. Threat Analysis
[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.
13. Acknowledgements 14. Acknowledgements
The authors would like to thank Erwann Abelea, Robin Alden, Al The authors would like to thank Erwann Abelea, Robin Alden, Al
Cutter, Francis Dupont, Adam Eijdenberg, Stephen Farrell, Daniel Kahn Cutter, Francis Dupont, Adam Eijdenberg, Stephen Farrell, Daniel Kahn
Gillmor, Paul Hadfield, Brad Hill, Jeff Hodges, Paul Hoffman, Jeffrey Gillmor, Paul Hadfield, Brad Hill, Jeff Hodges, Paul Hoffman, Jeffrey
Hutzelman, Kat Joyce, Stephen Kent, SM, Alexey Melnikov, Linus Hutzelman, Kat Joyce, Stephen Kent, SM, Alexey Melnikov, Linus
Nordberg, Chris Palmer, Trevor Perrin, Pierre Phaneuf, Melinda Shore, Nordberg, Chris Palmer, Trevor Perrin, Pierre Phaneuf, Melinda Shore,
Ryan Sleevi, Martin Smith, Carl Wallace and Paul Wouters for their Ryan Sleevi, Martin Smith, Carl Wallace and Paul Wouters for their
valuable contributions. 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.
14. References 15. References
14.1. Normative References 15.1. Normative References
[DSS] National Institute of Standards and Technology, "Digital [DSS] National Institute of Standards and Technology, "Digital
Signature Standard (DSS)", FIPS 186-3, June 2009, Signature Standard (DSS)", FIPS 186-3, June 2009,
<http://csrc.nist.gov/publications/fips/fips186-3/ <http://csrc.nist.gov/publications/fips/fips186-3/
fips_186-3.pdf>. fips_186-3.pdf>.
[FIPS.180-4] [FIPS.180-4]
National Institute of Standards and Technology, "Secure National Institute of Standards and Technology, "Secure
Hash Standard", FIPS PUB 180-4, March 2012, Hash Standard", FIPS PUB 180-4, March 2012,
<http://csrc.nist.gov/publications/fips/fips180-4/ <http://csrc.nist.gov/publications/fips/fips180-4/
fips-180-4.pdf>. fips-180-4.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>.
[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, March 1997. Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., [RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999. Transfer Protocol -- HTTP/1.1", RFC 2616,
DOI 10.17487/RFC2616, June 1999,
<http://www.rfc-editor.org/info/rfc2616>.
[RFC3447] Jonsson, J. and B. Kaliski, "Public-Key Cryptography [RFC3447] Jonsson, J. and B. Kaliski, "Public-Key Cryptography
Standards (PKCS) #1: RSA Cryptography Specifications Standards (PKCS) #1: RSA Cryptography Specifications
Version 2.1", RFC 3447, February 2003. Version 2.1", RFC 3447, DOI 10.17487/RFC3447, February
2003, <http://www.rfc-editor.org/info/rfc3447>.
[RFC4627] Crockford, D., "The application/json Media Type for [RFC4627] Crockford, D., "The application/json Media Type for
JavaScript Object Notation (JSON)", RFC 4627, July 2006. JavaScript Object Notation (JSON)", RFC 4627,
DOI 10.17487/RFC4627, July 2006,
<http://www.rfc-editor.org/info/rfc4627>.
[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data [RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, October 2006. Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
<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, August 2008. (TLS) Protocol Version 1.2", RFC 5246,
DOI 10.17487/RFC5246, August 2008,
<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, May 2008. (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
<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., Burbank, J., and W. Kasch, "Network [RFC5905] Mills, D., Martin, J., Ed., Burbank, J., and W. Kasch,
Time Protocol Version 4: Protocol and Algorithms "Network Time Protocol Version 4: Protocol and Algorithms
Specification", RFC 5905, June 2010. Specification", RFC 5905, DOI 10.17487/RFC5905, June 2010,
<http://www.rfc-editor.org/info/rfc5905>.
[RFC6066] Eastlake, D., "Transport Layer Security (TLS) Extensions: [RFC6066] Eastlake 3rd, D., "Transport Layer Security (TLS)
Extension Definitions", RFC 6066, January 2011. Extensions: Extension Definitions", RFC 6066,
DOI 10.17487/RFC6066, January 2011,
<http://www.rfc-editor.org/info/rfc6066>.
[RFC6125] Saint-Andre, P. and J. Hodges, "Representation and [RFC6125] Saint-Andre, P. and J. Hodges, "Representation and
Verification of Domain-Based Application Service Identity Verification of Domain-Based Application Service Identity
within Internet Public Key Infrastructure Using X.509 within Internet Public Key Infrastructure Using X.509
(PKIX) Certificates in the Context of Transport Layer (PKIX) Certificates in the Context of Transport Layer
Security (TLS)", RFC 6125, March 2011. Security (TLS)", RFC 6125, DOI 10.17487/RFC6125, March
2011, <http://www.rfc-editor.org/info/rfc6125>.
[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,
skipping to change at page 49, line 19 skipping to change at page 51, line 42
[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>.
[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>.
14.2. Informative References 15.2. 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,
skipping to change at page 49, line 46 skipping to change at page 52, line 20
crosby.pdf>. crosby.pdf>.
[EVSSLGuidelines] [EVSSLGuidelines]
CA/Browser Forum, "Guidelines For The Issuance And CA/Browser Forum, "Guidelines For The Issuance And
Management Of Extended Validation Certificates", 2007, Management Of Extended Validation Certificates", 2007,
<https://cabforum.org/wp-content/uploads/ <https://cabforum.org/wp-content/uploads/
EV_Certificate_Guidelines.pdf>. EV_Certificate_Guidelines.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-01 (work in progress), CT", draft-ietf-trans-gossip-02 (work in progress), March
October 2015. 2016.
[I-D.ietf-trans-threat-analysis] [I-D.ietf-trans-threat-analysis]
Kent, S., "Attack Model and Threat for Certificate Kent, S., "Attack Model and Threat for Certificate
Transparency", draft-ietf-trans-threat-analysis-03 (work Transparency", draft-ietf-trans-threat-analysis-05 (work
in progress), October 2015. in progress), April 2016.
[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>.
[Public.Suffix.List] [Public.Suffix.List]
Mozilla Foundation, "Public Suffix List", 2016, <https:// Mozilla Foundation, "Public Suffix List", 2016,
publicsuffix.org>. <https://publicsuffix.org>.
[RFC6962] Laurie, B., Langley, A., and E. Kasper, "Certificate [RFC6962] Laurie, B., Langley, A., and E. Kasper, "Certificate
Transparency", RFC 6962, June 2013. Transparency", RFC 6962, DOI 10.17487/RFC6962, June 2013,
<http://www.rfc-editor.org/info/rfc6962>.
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
skipping to change at page 51, line 28 skipping to change at page 53, line 28
before submission of the TBSCertificate (inside a v1 precertificate, before submission of the TBSCertificate (inside a v1 precertificate,
as described in Section 3.1. of [RFC6962]) to a v1 log so that TLS as described in Section 3.1. of [RFC6962]) to a v1 log so that TLS
clients conforming to [RFC6962] but not this document are oblivious clients conforming to [RFC6962] but not this document are oblivious
to the embedded v2 SCTs. An issuer can follow these steps to produce to the embedded v2 SCTs. An issuer can follow these steps to produce
an X.509 certificate with embedded v1 and v2 SCTs: an X.509 certificate with embedded v1 and v2 SCTs:
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 8.1.2. Section 9.1.2.
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.
 End of changes. 116 change blocks. 
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