draft-ietf-trans-rfc6962-bis-18.txt   draft-ietf-trans-rfc6962-bis-19.txt 
Public Notary Transparency Working Group B. Laurie TRANS (Public Notary Transparency) B. Laurie
Internet-Draft A. Langley Internet-Draft A. Langley
Intended status: Standards Track E. Kasper Intended status: Standards Track E. Kasper
Expires: January 28, 2017 E. Messeri Expires: March 4, 2017 E. Messeri
Google Google
R. Stradling R. Stradling
Comodo Comodo
July 27, 2016 August 31, 2016
Certificate Transparency Certificate Transparency
draft-ietf-trans-rfc6962-bis-18 draft-ietf-trans-rfc6962-bis-19
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) server certificates as they are
observed, in a manner that allows anyone to audit certification issued or observed, in a manner that allows anyone to audit
authority (CA) activity and notice the issuance of suspect certification authority (CA) activity and notice the issuance of
certificates as well as to audit the certificate logs themselves. suspect certificates as well as to audit the certificate logs
The intent is that eventually clients would refuse to honor themselves. The intent is that eventually clients would refuse to
certificates that do not appear in a log, effectively forcing CAs to honor certificates that do not appear in a log, effectively forcing
add all issued certificates to the logs. CAs to add all issued certificates to the logs.
Logs are network services that implement the protocol operations for Logs are network services that implement the protocol operations for
submissions and queries that are defined in this document. submissions and queries that are defined in this document.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 28, 2017. This Internet-Draft will expire on March 4, 2017.
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
publication of this document. Please review these documents publication of this document. Please review these documents
skipping to change at page 2, line 31 skipping to change at page 2, line 31
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 . . . . . . . . . . . . . . . . . . . . . 10 2.1.4. Signatures . . . . . . . . . . . . . . . . . . . . . 10
3. Submitters . . . . . . . . . . . . . . . . . . . . . . . . . 11 3. Submitters . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.1. Certificates . . . . . . . . . . . . . . . . . . . . . . 11 3.1. Certificates . . . . . . . . . . . . . . . . . . . . . . 11
3.2. Precertificates . . . . . . . . . . . . . . . . . . . . . 11 3.2. Precertificates . . . . . . . . . . . . . . . . . . . . . 11
4. Private Domain Name Labels . . . . . . . . . . . . . . . . . 12 4. Private Domain Name Labels . . . . . . . . . . . . . . . . . 12
4.1. Wildcard Certificates . . . . . . . . . . . . . . . . . . 12 4.1. Wildcard Certificates . . . . . . . . . . . . . . . . . . 12
4.2. Redaction of Domain Name Labels . . . . . . . . . . . . . 13 4.2. Using a Name-Constrained Intermediate CA . . . . . . . . 12
4.2.1. Redacting Labels in Precertificates . . . . . . . . . 13 5. Log Format and Operation . . . . . . . . . . . . . . . . . . 13
4.2.2. redactedSubjectAltName Certificate Extension . . . . 13 5.1. Accepting Submissions . . . . . . . . . . . . . . . . . . 14
4.3. Using a Name-Constrained Intermediate CA . . . . . . . . 14 5.2. Log Entries . . . . . . . . . . . . . . . . . . . . . . . 14
5. Log Format and Operation . . . . . . . . . . . . . . . . . . 15 5.3. Log ID . . . . . . . . . . . . . . . . . . . . . . . . . 15
5.1. Accepting Submissions . . . . . . . . . . . . . . . . . . 16 5.4. TransItem Structure . . . . . . . . . . . . . . . . . . . 16
5.2. Log Entries . . . . . . . . . . . . . . . . . . . . . . . 16 5.5. Merkle Tree Leaves . . . . . . . . . . . . . . . . . . . 17
5.3. Log ID . . . . . . . . . . . . . . . . . . . . . . . . . 17 5.6. Signed Certificate Timestamp (SCT) . . . . . . . . . . . 18
5.4. TransItem Structure . . . . . . . . . . . . . . . . . . . 18 5.7. Merkle Tree Head . . . . . . . . . . . . . . . . . . . . 19
5.5. Merkle Tree Leaves . . . . . . . . . . . . . . . . . . . 19 5.8. Signed Tree Head (STH) . . . . . . . . . . . . . . . . . 20
5.6. Signed Certificate Timestamp (SCT) . . . . . . . . . . . 20 5.9. Merkle Consistency Proofs . . . . . . . . . . . . . . . . 21
5.7. Merkle Tree Head . . . . . . . . . . . . . . . . . . . . 21 5.10. Merkle Inclusion Proofs . . . . . . . . . . . . . . . . . 21
5.8. Signed Tree Head (STH) . . . . . . . . . . . . . . . . . 21 5.11. Shutting down a log . . . . . . . . . . . . . . . . . . . 22
5.9. Merkle Consistency Proofs . . . . . . . . . . . . . . . . 23 6. Log Client Messages . . . . . . . . . . . . . . . . . . . . . 22
5.10. Merkle Inclusion Proofs . . . . . . . . . . . . . . . . . 23 6.1. Add Chain to Log . . . . . . . . . . . . . . . . . . . . 24
5.11. Shutting down a log . . . . . . . . . . . . . . . . . . . 24 6.2. Add PreCertChain to Log . . . . . . . . . . . . . . . . . 25
6. Log Client Messages . . . . . . . . . . . . . . . . . . . . . 24 6.3. Retrieve Latest Signed Tree Head . . . . . . . . . . . . 25
6.1. Add Chain to Log . . . . . . . . . . . . . . . . . . . . 26
6.2. Add PreCertChain to Log . . . . . . . . . . . . . . . . . 27
6.3. Retrieve Latest Signed Tree Head . . . . . . . . . . . . 27
6.4. Retrieve Merkle Consistency Proof between Two Signed Tree 6.4. Retrieve Merkle Consistency Proof between Two Signed Tree
Heads . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Heads . . . . . . . . . . . . . . . . . . . . . . . . . . 25
6.5. Retrieve Merkle Inclusion Proof from Log by Leaf Hash . . 28 6.5. Retrieve Merkle Inclusion Proof from Log by Leaf Hash . . 26
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 . . . . . . . . . . . . . 29 Consistency Proof by Leaf Hash . . . . . . . . . . . . . 27
6.7. Retrieve Entries and STH from Log . . . . . . . . . . . . 30 6.7. Retrieve Entries and STH from Log . . . . . . . . . . . . 29
6.8. Retrieve Accepted Trust Anchors . . . . . . . . . . . . . 32 6.8. Retrieve Accepted Trust Anchors . . . . . . . . . . . . . 30
7. Optional Client Messages . . . . . . . . . . . . . . . . . . 32 7. Optional Client Messages . . . . . . . . . . . . . . . . . . 30
7.1. Get Entry Number for SCT . . . . . . . . . . . . . . . . 32 7.1. Get Entry Number for SCT . . . . . . . . . . . . . . . . 30
7.2. Get Entry Numbers for Certificate . . . . . . . . . . . . 33 7.2. Get Entry Numbers for TBSCertificate . . . . . . . . . . 31
8. TLS Servers . . . . . . . . . . . . . . . . . . . . . . . . . 33 8. TLS Servers . . . . . . . . . . . . . . . . . . . . . . . . . 32
8.1. Multiple SCTs . . . . . . . . . . . . . . . . . . . . . . 34 8.1. Multiple SCTs . . . . . . . . . . . . . . . . . . . . . . 33
8.2. TransItemList Structure . . . . . . . . . . . . . . . . . 35 8.2. TransItemList Structure . . . . . . . . . . . . . . . . . 33
8.3. Presenting SCTs, inclusion proofs and STHs . . . . . . . 35 8.3. Presenting SCTs, inclusion proofs and STHs . . . . . . . 34
8.4. Presenting SCTs only . . . . . . . . . . . . . . . . . . 36 8.4. Presenting SCTs only . . . . . . . . . . . . . . . . . . 34
8.5. transparency_info TLS Extension . . . . . . . . . . . . . 36 8.5. transparency_info TLS Extension . . . . . . . . . . . . . 34
9. Certification Authorities . . . . . . . . . . . . . . . . . . 36 8.6. cached_info TLS Extension . . . . . . . . . . . . . . . . 35
9.1. Transparency Information X.509v3 Extension . . . . . . . 36 9. Certification Authorities . . . . . . . . . . . . . . . . . . 35
9.1.1. OCSP Response Extension . . . . . . . . . . . . . . . 36 9.1. Transparency Information X.509v3 Extension . . . . . . . 35
9.1.2. Certificate Extension . . . . . . . . . . . . . . . . 37 9.1.1. OCSP Response Extension . . . . . . . . . . . . . . . 35
9.2. TLS Feature Extension . . . . . . . . . . . . . . . . . . 37 9.1.2. Certificate Extension . . . . . . . . . . . . . . . . 36
10. Clients . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 9.2. TLS Feature Extension . . . . . . . . . . . . . . . . . . 36
10.1. Metadata . . . . . . . . . . . . . . . . . . . . . . . . 37 10. Clients . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
10.2. TLS Client . . . . . . . . . . . . . . . . . . . . . . . 38 10.1. Metadata . . . . . . . . . . . . . . . . . . . . . . . . 36
10.2.1. Receiving SCTs . . . . . . . . . . . . . . . . . . . 38 10.2. TLS Client . . . . . . . . . . . . . . . . . . . . . . . 37
10.2.2. Reconstructing the TBSCertificate . . . . . . . . . 38 10.2.1. Receiving SCTs . . . . . . . . . . . . . . . . . . . 37
10.2.3. Verifying the redactedSubjectAltName extension . . . 39 10.2.2. Reconstructing the TBSCertificate . . . . . . . . . 37
10.2.4. Validating SCTs . . . . . . . . . . . . . . . . . . 39 10.2.3. Validating SCTs . . . . . . . . . . . . . . . . . . 38
10.2.5. Validating inclusion proofs . . . . . . . . . . . . 40 10.2.4. Validating inclusion proofs . . . . . . . . . . . . 38
10.2.6. Evaluating compliance . . . . . . . . . . . . . . . 40 10.2.5. Evaluating compliance . . . . . . . . . . . . . . . 39
10.2.7. TLS Feature Extension . . . . . . . . . . . . . . . 40 10.2.6. TLS Feature Extension . . . . . . . . . . . . . . . 39
10.2.8. Handling of Non-compliance . . . . . . . . . . . . . 41 10.2.7. cached_info TLS Extension . . . . . . . . . . . . . 39
10.3. Monitor . . . . . . . . . . . . . . . . . . . . . . . . 41 10.2.8. Handling of Non-compliance . . . . . . . . . . . . . 39
10.4. Auditing . . . . . . . . . . . . . . . . . . . . . . . . 42 10.3. Monitor . . . . . . . . . . . . . . . . . . . . . . . . 39
10.4.1. Verifying an inclusion proof . . . . . . . . . . . . 43 10.4. Auditing . . . . . . . . . . . . . . . . . . . . . . . . 40
10.4.2. Verifying consistency between two STHs . . . . . . . 43 10.4.1. Verifying an inclusion proof . . . . . . . . . . . . 41
10.4.3. Verifying root hash given entries . . . . . . . . . 44 10.4.2. Verifying consistency between two STHs . . . . . . . 42
11. Algorithm Agility . . . . . . . . . . . . . . . . . . . . . . 45 10.4.3. Verifying root hash given entries . . . . . . . . . 43
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 46 11. Algorithm Agility . . . . . . . . . . . . . . . . . . . . . . 44
12.1. TLS Extension Type . . . . . . . . . . . . . . . . . . . 46 12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 44
12.2. Hash Algorithms . . . . . . . . . . . . . . . . . . . . 46 12.1. TLS Extension Type . . . . . . . . . . . . . . . . . . . 44
12.3. Signature Algorithms . . . . . . . . . . . . . . . . . . 46 12.2. New Entry to the TLS CachedInformationType registry . . 44
12.4. SCT Extensions . . . . . . . . . . . . . . . . . . . . . 46 12.3. Hash Algorithms . . . . . . . . . . . . . . . . . . . . 44
12.5. STH Extensions . . . . . . . . . . . . . . . . . . . . . 47 12.4. Signature Algorithms . . . . . . . . . . . . . . . . . . 45
12.6. Object Identifiers . . . . . . . . . . . . . . . . . . . 47 12.5. SCT Extensions . . . . . . . . . . . . . . . . . . . . . 45
12.6.1. Log ID Registry 1 . . . . . . . . . . . . . . . . . 47 12.6. STH Extensions . . . . . . . . . . . . . . . . . . . . . 45
12.6.2. Log ID Registry 2 . . . . . . . . . . . . . . . . . 47 12.7. Object Identifiers . . . . . . . . . . . . . . . . . . . 45
13. Security Considerations . . . . . . . . . . . . . . . . . . . 48 12.7.1. Log ID Registry 1 . . . . . . . . . . . . . . . . . 46
13.1. Misissued Certificates . . . . . . . . . . . . . . . . . 48 12.7.2. Log ID Registry 2 . . . . . . . . . . . . . . . . . 46
13.2. Detection of Misissue . . . . . . . . . . . . . . . . . 48 13. Security Considerations . . . . . . . . . . . . . . . . . . . 46
13.3. Avoiding Overly Redacting Domain Name Labels . . . . . . 48 13.1. Misissued Certificates . . . . . . . . . . . . . . . . . 47
13.4. Misbehaving Logs . . . . . . . . . . . . . . . . . . . . 49 13.2. Detection of Misissue . . . . . . . . . . . . . . . . . 47
13.5. Deterministic Signatures . . . . . . . . . . . . . . . . 49 13.3. Misbehaving Logs . . . . . . . . . . . . . . . . . . . . 47
13.6. Multiple SCTs . . . . . . . . . . . . . . . . . . . . . 50 13.4. Deterministic Signatures . . . . . . . . . . . . . . . . 48
14. Privacy Considerations . . . . . . . . . . . . . . . . . . . 50 13.5. Multiple SCTs . . . . . . . . . . . . . . . . . . . . . 48
14.1. Ensuring Effective Redaction . . . . . . . . . . . . . . 50 14. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 48
15. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 50 15. References . . . . . . . . . . . . . . . . . . . . . . . . . 48
16. References . . . . . . . . . . . . . . . . . . . . . . . . . 51 15.1. Normative References . . . . . . . . . . . . . . . . . . 48
16.1. Normative References . . . . . . . . . . . . . . . . . . 51 15.2. Informative References . . . . . . . . . . . . . . . . . 50
16.2. Informative References . . . . . . . . . . . . . . . . . 52 Appendix A. Supporting v1 and v2 simultaneously . . . . . . . . 51
Appendix A. Supporting v1 and v2 simultaneously . . . . . . . . 54 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 52
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 that could be
document, we only describe its use for public TLS server certificates used for transparently logging any form of binary data, subject to
issued by public certification authorities (CAs). some kind of inclusion criteria. In this document, we only describe
its use for public TLS server certificates (i.e., where the inclusion
criteria is a valid certificate issued by a public certification
authority (CA)).
Each log contains 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 for which they are responsible have had certificates issued domains for which they are responsible have had certificates issued
that 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. However, broadly speaking, they
invoke existing business mechanisms for dealing with misissued can 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
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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 (see Section 10.1). We part of the metadata relating to that log (see Section 10.1). We
have established a registry of acceptable algorithms, see have established a registry of acceptable algorithms, see
Section 12.2. The hashing algorithm in use is referred to as HASH Section 12.3. The hashing algorithm in use is referred to as HASH
throughout this document and the size of its output in bytes as throughout this document and the size of its output in bytes as
HASH_SIZE. The input to the Merkle Tree Hash is a list of data HASH_SIZE. The input to the Merkle Tree Hash is a list of data
entries; these entries will be hashed to form the leaves of the entries; these entries will be hashed to form the leaves of the
Merkle Hash Tree. The output is a single HASH_SIZE Merkle Tree Hash. Merkle Hash Tree. The output is a single HASH_SIZE Merkle Tree Hash.
Given an ordered list of n inputs, D[n] = {d(0), d(1), ..., d(n-1)}, Given an ordered list of n inputs, D[n] = {d(0), d(1), ..., d(n-1)},
the Merkle Tree Hash (MTH) is thus defined as follows: the 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().
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MTH({d(0)}) = HASH(0x00 || d(0)). MTH({d(0)}) = HASH(0x00 || d(0)).
For n > 1, let k be the largest power of two smaller than n (i.e., k For n > 1, let k be the largest power of two smaller than n (i.e., k
< n <= 2k). The Merkle Tree Hash of an n-element list D[n] is then < n <= 2k). The Merkle Tree Hash of an n-element list D[n] is then
defined recursively as defined recursively as
MTH(D[n]) = HASH(0x01 || MTH(D[0:k]) || MTH(D[k:n])), MTH(D[n]) = HASH(0x01 || MTH(D[0:k]) || MTH(D[k:n])),
where || is concatenation and D[k1:k2] denotes the list {d(k1), where || is concatenation and D[k1:k2] denotes the list {d(k1),
d(k1+1),..., d(k2-1)} of length (k2 - k1). (Note that the hash d(k1+1), ..., d(k2-1)} of length (k2 - k1). (Note that the hash
calculations for leaves and nodes differ. This domain separation is calculations for leaves and nodes differ. This domain separation is
required to give second preimage resistance.) required to give second preimage resistance.)
Note that we do not require the length of the input list to be a Note that we do not require the length of the input list to be a
power of two. The resulting Merkle Tree may thus not be balanced; power of two. The resulting Merkle Tree may thus not be balanced;
however, its shape is uniquely determined by the number of leaves. however, its shape is uniquely determined by the number of leaves.
(Note: This Merkle Tree is essentially the same as the history tree (Note: This Merkle Tree is essentially the same as the history tree
[CrosbyWallach] proposal, except our definition handles non-full [CrosbyWallach] proposal, except our definition handles non-full
trees differently.) trees differently.)
skipping to change at page 7, line 14 skipping to change at page 7, line 14
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.
skipping to change at page 8, line 14 skipping to change at page 8, line 14
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
skipping to change at page 10, line 34 skipping to change at page 10, line 32
/ \ / \ / \ / \ / \ / \ / \ / \
/ \ e f / \ / \ / \ e f / \ / \
/ \ | | / \ / \ / \ | | / \ / \
g h d4 d5 g h i j g h d4 d5 g h i j
/ \ / \ / \ / \ / \ | / \ / \ / \ / \ / \ |
a b c d a b c d e f d6 a b c d a b c d e f d6
| | | | | | | | | | | | | | | | | | | |
d0 d1 d2 d3 d0 d1 d2 d3 d4 d5 d0 d1 d2 d3 d0 d1 d2 d3 d4 d5
The consistency proof between hash0 and hash is PROOF(3, D[7]) = [c, The consistency proof between hash0 and hash is PROOF(3, D[7]) = [c,
d, g, l]. c, g are used to verify hash0, and d, l are additionally d, g, l]. c, g are used to verify hash0, and d, l are additionally
used to show hash is consistent with hash0. used to show hash is consistent with hash0.
The consistency proof between hash1 and hash is PROOF(4, D[7]) = [l]. The consistency proof between hash1 and hash is PROOF(4, D[7]) = [l].
hash can be verified using hash1=k and l. hash can be verified using hash1=k and l.
The consistency proof between hash2 and hash is PROOF(6, D[7]) = [i, The consistency proof between hash2 and hash is PROOF(6, D[7]) = [i,
j, k]. k, i are used to verify hash2, and j is additionally used to j, k]. k, i are used to verify hash2, and j is additionally used to
show hash is consistent with hash2. show hash is consistent with hash2.
2.1.4. Signatures 2.1.4. 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 12.3. signature algorithms defined in Section 12.4.
3. Submitters 3. Submitters
Submitters submit certificates or preannouncements of certificates Submitters submit certificates or preannouncements of certificates
prior to issuance (precertificates) to logs for public auditing, as prior to issuance (precertificates) to logs for public auditing, as
described below. In order to enable attribution of each logged described below. In order to enable attribution of each logged
certificate or precertificate to its issuer, each submission MUST be certificate or precertificate to its issuer, each submission MUST be
accompanied by all additional certificates required to verify the accompanied by all additional certificates required to verify the
chain up to an accepted trust anchor. The trust anchor (a root or chain up to an accepted trust anchor. The trust anchor (a root or
intermediate CA certificate) MAY be omitted from the submission. intermediate CA certificate) MAY be omitted from the submission.
skipping to change at page 11, line 35 skipping to change at page 11, line 28
Any entity can submit a certificate (Section 6.1) to a log. Since it Any entity can submit a certificate (Section 6.1) to a log. Since it
is anticipated that TLS clients will reject certificates that are not is anticipated that TLS clients will reject certificates that are not
logged, it is expected that certificate issuers and subjects will be logged, it is expected that certificate issuers and subjects will be
strongly motivated to submit them. strongly motivated to submit them.
3.2. Precertificates 3.2. Precertificates
CAs may preannounce a certificate prior to issuance by submitting a CAs may preannounce a certificate prior to issuance by submitting a
precertificate (Section 6.2) that the log can use to create an entry precertificate (Section 6.2) that the log can use to create an entry
that will be valid against the issued certificate. The CA MAY that will be valid against the issued certificate. The CA MAY
incorporate the returned SCT in the issued certificate. Examples of incorporate the returned SCT in the issued certificate. One example
situations where the returned SCT is not incorporated into the issued of where the returned SCT is not incorporated in the issued
certificate would be when a CA sends the precertificate to multiple certificate is when a CA sends the precertificate to multiple logs,
logs, but only incorporates the SCTs that are returned first, or the but only incorporates the SCTs that are returned first.
CA is using domain name redaction (Section 4.2) and intends to use
another mechanism to publish SCTs (such as an OCSP response
(Section 9.1.1) 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
TBSCertificate [RFC5280] that will be identical to the TBSCertificate [RFC5280] that will be identical to the
TBSCertificate in the issued certificate, except that: TBSCertificate in the issued certificate, except that the
Transparency Information (Section 9.1) extension MUST be omitted.
* the Transparency Information (Section 9.1) extension MUST be
omitted.
* the subjectAltName [RFC5280] extension MUST be omitted when the
redactedSubjectAltName (Section 4.2.2) extension is present.
o "SignedData.signerInfos" MUST contain a signature from the same o "SignedData.signerInfos" MUST contain a signature from the same
(root or intermediate) CA that will ultimately issue the (root or intermediate) CA that will ultimately issue the
certificate. This signature indicates the CA's intent to issue certificate. This signature indicates the CA's intent to issue
the certificate. This intent is considered binding (i.e. the certificate. This intent is considered binding (i.e.,
misissuance of the precertificate is considered equivalent to misissuance of the precertificate is considered equivalent to
misissuance of the certificate). (Note that, because of the misissuance of the certificate). (Note that, because of the
structure of CMS, the signature on the CMS object will not be a structure of CMS, the signature on the CMS object will not be a
valid X.509v3 signature and so cannot be used to construct a valid X.509v3 signature and so cannot be used to construct a
certificate from the precertificate). certificate from the precertificate).
o "SignedData.certificates" SHOULD be omitted. o "SignedData.certificates" SHOULD be omitted.
4. Private Domain Name Labels 4. Private Domain Name Labels
Some regard certain DNS domain name labels within their registered Some regard certain DNS domain name labels within their registered
domain space as private and security sensitive. Even though these domain space as private and security sensitive. Even though these
domains are often only accessible within the domain owner's private domains are often only accessible within the domain owner's private
network, it's common for them to be secured using publicly trusted network, it's common for them to be secured using publicly trusted
TLS server certificates. We define a mechanism (see Section 4.2) to TLS server certificates.
allow these private labels to not appear in public logs, while still
retaining most of the security benefits that accrue from using
Certificate Transparency mechanisms.
4.1. Wildcard Certificates 4.1. Wildcard Certificates
A certificate containing a DNS-ID [RFC6125] of "*.example.com" could A certificate containing a DNS-ID [RFC6125] of "*.example.com" could
be used to secure the domain "topsecret.example.com", without be used to secure the domain "topsecret.example.com", without
revealing the string "topsecret" publicly. revealing the string "topsecret" publicly.
Since TLS clients only match the wildcard character to the complete Since TLS clients only match the wildcard character to the complete
leftmost label of the DNS domain name (see Section 6.4.3 of leftmost label of the DNS domain name (see Section 6.4.3 of
[RFC6125]), a different approach is needed when any label other than [RFC6125]), a different approach is needed when any label other than
the leftmost label in a DNS-ID is considered private (e.g. the leftmost label in a DNS-ID is considered private (e.g.,
"top.secret.example.com"). Also, wildcard certificates are "top.secret.example.com"). Also, wildcard certificates are
prohibited in some cases, such as Extended Validation Certificates prohibited in some cases, such as Extended Validation Certificates
[EVSSLGuidelines]. [EVSSLGuidelines].
4.2. Redaction of Domain Name Labels 4.2. Using a Name-Constrained Intermediate CA
4.2.1. Redacting Labels in Precertificates
When creating a precertificate, the CA MAY omit the subjectAltName
extension, even if it intends to include the extension in the final
certificate. If omitting the subjectAltName extension, the CA MUST
include a redactedSubjectAltName (Section 4.2.2) extension that
contains, in a redacted form, the same entries that will be included
in the certificate's subjectAltName extension.
Wildcard "*" labels MUST NOT be redacted, but one or more non-
wildcard labels in each DNS-ID [RFC6125] can each be replaced with a
redacted label as follows:
REDACT(label) = prefix || BASE32(index || _label_hash)
_label_hash = LABELHASH(keyid_len || keyid || label_len || label)
"label" is the case-sensitive label to be redacted.
"prefix" is the "?" character (ASCII value 63).
"index" is the 1 byte index of a hash function in Section 12.2. The
value 255 is reserved.
"keyid_len" is the 1 byte length of the "keyid".
"keyid" is the keyIdentifier from the Subject Key Identifier
extension (section 4.2.1.2 of [RFC5280]), excluding the ASN.1 OCTET
STRING tag and length bytes.
"label_len" is the 1 byte length of the "label".
"||" denotes concatenation.
"BASE32" is the Base 32 Encoding function (section 6 of [RFC4648]).
Pad characters MUST NOT be appended to the encoded data.
"LABELHASH" is the hash function identified by "index".
4.2.2. redactedSubjectAltName Certificate Extension
The redactedSubjectAltName extension is a non-critical extension (OID
1.3.101.77) that is identical in structure to the subjectAltName
extension, except that DNS-IDs MAY contain redacted labels (see
Section 4.2.1).
When used, the redactedSubjectAltName extension MUST be present in
both the precertificate and the corresponding certificate.
This extension informs TLS clients of the DNS-ID labels that were
redacted and the degree of redaction, while minimizing the complexity
of TBSCertificate reconstruction (as described in Section 10.2.2).
Hashing the redacted labels allows the legitimate domain owner to
identify whether or not each redacted label correlates to a label
they know of.
Only DNS-ID labels can be redacted using this mechanism. However,
CAs can use Name Constraints (Section 4.3) to allow DNS domain name
labels in other subjectAltName entries to not appear in logs.
4.3. Using a Name-Constrained Intermediate CA
An intermediate CA certificate or intermediate CA precertificate that An intermediate CA certificate or intermediate CA precertificate that
contains the Name Constraints [RFC5280] extension MAY be logged in contains the Name Constraints [RFC5280] extension MAY be logged in
place of end-entity certificates issued by that intermediate CA, as place of end-entity certificates issued by that intermediate CA, as
long as all of the following conditions are met: long as all of the following conditions are met:
o there MUST be a non-critical extension (OID 1.3.101.76, whose o there MUST be a non-critical extension (OID 1.3.101.76, whose
extnValue OCTET STRING contains ASN.1 NULL data (0x05 0x00)). extnValue OCTET STRING contains ASN.1 NULL data (0x05 0x00)).
This extension is an explicit indication that it is acceptable to This extension is an explicit indication that it is acceptable to
not log certificates issued by this intermediate CA. not log certificates issued by this intermediate CA.
o permittedSubtrees MUST specify one or more dNSNames. o there MUST be a Name Constraints extension, in which:
o excludedSubtrees MUST specify the entire IPv4 and IPv6 address * permittedSubtrees MUST specify one or more dNSNames.
ranges.
* excludedSubtrees MUST specify the entire IPv4 and IPv6 address
ranges.
Below is an example Name Constraints extension that meets these Below is an example Name Constraints extension that meets these
conditions: conditions:
SEQUENCE { SEQUENCE {
OBJECT IDENTIFIER '2 5 29 30' OBJECT IDENTIFIER '2 5 29 30'
OCTET STRING, encapsulates { OCTET STRING, encapsulates {
SEQUENCE { SEQUENCE {
[0] { [0] {
SEQUENCE { SEQUENCE {
skipping to change at page 15, line 40 skipping to change at page 13, line 40
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 13.5). If different SCTs are clients as described in Section 13.4). If different SCTs are
produced for the same submission, multiple log entries will have to produced for the same submission, multiple log entries will have to
be created, one for each SCT (as the timestamp is a part of the leaf be created, one for each SCT (as the timestamp is a part of the leaf
structure). Note that if a certificate was previously logged as a structure). Note that if a certificate was previously logged as a
precertificate, then the precertificate's SCT of type precertificate, then the precertificate's SCT of type
"precert_sct_v2" would not be appropriate; instead, a fresh SCT of "precert_sct_v2" would not be appropriate; instead, a fresh SCT of
type "x509_sct_v2" should be generated. 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.
skipping to change at page 17, line 47 skipping to change at page 15, line 43
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 identified by an OID, which is specified in the log's Each log is identified by an OID, which is specified in the log's
metadata and which MUST NOT be used to identify any other log. A metadata and which MUST NOT be used to identify any other log. A
log's operator MUST either allocate the OID themselves or request an log's operator MUST either allocate the OID themselves or request an
OID from one of the two Log ID Registries (see Section 12.6.1 and OID from one of the two Log ID Registries (see Section 12.7.1 and
Section 12.6.2). Various data structures include the DER encoding of Section 12.7.2). Various data structures include the DER encoding of
this OID, excluding the ASN.1 tag and length bytes, in an opaque this OID, excluding the ASN.1 tag and length bytes, in an opaque
vector: vector:
opaque LogID<2..127>; opaque LogID<2..127>;
Note that the ASN.1 length and the opaque vector length are identical Note that the ASN.1 length and the opaque vector length are identical
in size (1 byte) and value, so the DER encoding of the OID can be in size (1 byte) and value, so the DER encoding of the OID can be
reproduced simply by prepending an OBJECT IDENTIFIER tag (0x06) to reproduced simply by prepending an OBJECT IDENTIFIER tag (0x06) to
the opaque vector length and contents. the opaque vector length and contents.
OIDs used to identify logs are limited such that the DER encoding of
their value is less than or equal to 127 octets.
5.4. TransItem Structure 5.4. TransItem Structure
Various data structures are encapsulated in the "TransItem" structure Various data structures are encapsulated in the "TransItem" structure
to ensure that the type and version of each one is identified in a to ensure that the type and version of each one is identified in a
common fashion: common fashion:
enum { enum {
reserved(0), reserved(0),
x509_entry_v2(1), precert_entry_v2(2), x509_entry_v2(1), precert_entry_v2(2),
x509_sct_v2(3), precert_sct_v2(4), x509_sct_v2(3), precert_sct_v2(4),
tree_head_v2(5), signed_tree_head_v2(6), signed_tree_head_v2(5), consistency_proof_v2(6),
consistency_proof_v2(7), inclusion_proof_v2(8), inclusion_proof_v2(7), x509_sct_with_proof_v2(8),
x509_sct_with_proof_v2(9), precert_sct_with_proof_v2(10), precert_sct_with_proof_v2(9),
(65535) (65535)
} VersionedTransType; } VersionedTransType;
struct { struct {
VersionedTransType versioned_type; VersionedTransType versioned_type;
select (versioned_type) { select (versioned_type) {
case x509_entry_v2: TimestampedCertificateEntryDataV2; case x509_entry_v2: TimestampedCertificateEntryDataV2;
case precert_entry_v2: TimestampedCertificateEntryDataV2; case precert_entry_v2: TimestampedCertificateEntryDataV2;
case x509_sct_v2: SignedCertificateTimestampDataV2; case x509_sct_v2: SignedCertificateTimestampDataV2;
case precert_sct_v2: SignedCertificateTimestampDataV2; case precert_sct_v2: SignedCertificateTimestampDataV2;
case tree_head_v2: TreeHeadDataV2;
case signed_tree_head_v2: SignedTreeHeadDataV2; case signed_tree_head_v2: SignedTreeHeadDataV2;
case consistency_proof_v2: ConsistencyProofDataV2; case consistency_proof_v2: ConsistencyProofDataV2;
case inclusion_proof_v2: InclusionProofDataV2; case inclusion_proof_v2: InclusionProofDataV2;
case x509_sct_with_proof_v2: SCTWithProofDataV2; case x509_sct_with_proof_v2: SCTWithProofDataV2;
case precert_sct_with_proof_v2: SCTWithProofDataV2; case precert_sct_with_proof_v2: SCTWithProofDataV2;
} data; } data;
} TransItem; } TransItem;
"versioned_type" is the type of the encapsulated data structure and "versioned_type" is the type of the encapsulated data structure and
the earliest version of this protocol to which it conforms. This the earliest version of this protocol to which it conforms. This
skipping to change at page 19, line 25 skipping to change at page 17, line 25
(see Section 5.2). Each leaf is the leaf hash (Section 2.1) of a (see Section 5.2). Each leaf is the leaf hash (Section 2.1) of a
"TransItem" structure of type "x509_entry_v2" or "precert_entry_v2", "TransItem" structure of type "x509_entry_v2" or "precert_entry_v2",
which encapsulates a "TimestampedCertificateEntryDataV2" structure. which encapsulates a "TimestampedCertificateEntryDataV2" structure.
Note that leaf hashes are calculated as HASH(0x00 || TransItem), Note that leaf hashes are calculated as HASH(0x00 || TransItem),
where the hashing algorithm is specified in the log's metadata. where the hashing algorithm is specified in the log's metadata.
opaque TBSCertificate<1..2^24-1>; opaque TBSCertificate<1..2^24-1>;
struct { struct {
uint64 timestamp; uint64 timestamp;
opaque issuer_key_hash[HASH_SIZE]; opaque issuer_key_hash<32..2^8-1>;
TBSCertificate tbs_certificate; TBSCertificate tbs_certificate;
SctExtension sct_extensions<0..2^16-1>; SctExtension sct_extensions<0..2^16-1>;
} TimestampedCertificateEntryDataV2; } TimestampedCertificateEntryDataV2;
"timestamp" is the NTP Time [RFC5905] at which the certificate or "timestamp" is the NTP Time [RFC5905] at which the certificate or
precertificate was accepted by the log, measured in milliseconds precertificate was accepted by the log, measured in milliseconds
since the epoch (January 1, 1970, 00:00), ignoring leap seconds. since the epoch (January 1, 1970, 00:00 UTC), ignoring leap seconds.
Note that the leaves of a log's Merkle Tree are not required to be in Note that the leaves of a log's Merkle Tree are not required to be in
strict chronological order. strict chronological order.
"issuer_key_hash" is the HASH of the public key of the CA that issued "issuer_key_hash" is the HASH of the public key of the CA that issued
the certificate or precertificate, calculated over the DER encoding the certificate or precertificate, calculated over the DER encoding
of the key represented as SubjectPublicKeyInfo [RFC5280]. This is of the key represented as SubjectPublicKeyInfo [RFC5280]. This is
needed to bind the CA to the certificate or precertificate, making it needed to bind the CA to the certificate or precertificate, making it
impossible for the corresponding SCT to be valid for any other impossible for the corresponding SCT to be valid for any other
certificate or precertificate whose TBSCertificate matches certificate or precertificate whose TBSCertificate matches
"tbs_certificate". "tbs_certificate". The length of the "issuer_key_hash" MUST match
HASH_SIZE.
"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 10.2.2). 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)
skipping to change at page 20, line 37 skipping to change at page 18, line 37
} 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 12.4. 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 "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
skipping to change at page 21, line 12 skipping to change at page 19, line 12
it SHOULD ignore that extension. Furthermore, an implementation MAY it SHOULD ignore that extension. Furthermore, an implementation MAY
choose to ignore any extension(s) that it does understand. choose to ignore any extension(s) that it does understand.
The encoding of the digitally-signed element is defined in [RFC5246]. The encoding of the digitally-signed element is defined in [RFC5246].
"timestamped_entry" is a "TransItem" structure that MUST be of type "timestamped_entry" is a "TransItem" structure that MUST be of type
"x509_entry_v2" or "precert_entry_v2" (see Section 5.5). "x509_entry_v2" or "precert_entry_v2" (see Section 5.5).
5.7. Merkle Tree Head 5.7. Merkle Tree Head
The log stores information about its Merkle Tree in a "TransItem" The log stores information about its Merkle Tree in a
structure of type "tree_head_v2", which encapsulates a "TreeHeadDataV2":
"TreeHeadDataV2" structure:
opaque NodeHash[HASH_SIZE]; opaque NodeHash<32..2^8-1>;
enum {
reserved(65535)
} SthExtensionType;
struct {
SthExtensionType sth_extension_type;
opaque sth_extension_data<0..2^16-1>;
} SthExtension;
struct { struct {
uint64 timestamp; uint64 timestamp;
uint64 tree_size; uint64 tree_size;
NodeHash root_hash; NodeHash root_hash;
SthExtension sth_extensions<0..2^16-1>; SthExtension sth_extensions<0..2^16-1>;
} TreeHeadDataV2; } TreeHeadDataV2;
The length of NodeHash MUST match HASH_SIZE of the log.
"sth_extension_type" identifies a single extension from the IANA
registry in Section 12.6. At the time of writing, no extensions are
specified.
The interpretation of the "sth_extension_data" field is determined
solely by the value of the "sth_extension_type" field. Each document
that registers a new "sth_extension_type" must describe how to
interpret the corresponding "sth_extension_data".
"timestamp" is the current NTP Time [RFC5905], measured in "timestamp" is the current NTP Time [RFC5905], measured in
milliseconds since the epoch (January 1, 1970, 00:00), ignoring leap milliseconds since the epoch (January 1, 1970, 00:00 UTC), ignoring
seconds. leap seconds.
"tree_size" is the number of entries currently in the log's Merkle "tree_size" is the number of entries currently in the log's Merkle
Tree. Tree.
"root_hash" is the root of the Merkle Hash Tree. "root_hash" is the root of the Merkle Hash Tree.
"sth_extensions" matches the STH extensions of the corresponding STH. "sth_extensions" is a vector of 0 or more STH extensions. This
vector MUST NOT include more than one extension with the same
"sth_extension_type". The extensions in the vector MUST be ordered
by the value of the "sth_extension_type" field, smallest value first.
If an implementation sees an extension that it does not understand,
it SHOULD ignore that extension. Furthermore, an implementation MAY
choose to ignore any extension(s) that it does understand.
5.8. Signed Tree Head (STH) 5.8. Signed Tree Head (STH)
Periodically each log SHOULD sign its current tree head information Periodically each log SHOULD sign its current tree head information
(see Section 5.7) to produce an STH. When a client requests a log's (see Section 5.7) to produce an STH. When a client requests a log's
latest STH (see Section 6.3), the log MUST return an STH that is no latest STH (see Section 6.3), the log MUST return an STH that is no
older than the log's MMD. However, STHs could be used to mark older than the log's MMD. However, STHs could be used to mark
individual clients (by producing a new one for each query), so logs individual clients (by producing a new one for each query), so logs
MUST NOT produce them more frequently than is declared in their MUST NOT produce them more frequently than is declared in their
metadata. In general, there is no need to produce a new STH unless metadata. In general, there is no need to produce a new STH unless
there are new entries in the log; however, in the unlikely event that there are new entries in the log; however, in the unlikely event that
it receives no new submissions during an MMD period, the log SHALL it receives no new submissions during an MMD period, the log SHALL
sign the same Merkle Tree Hash with a fresh timestamp. sign the same Merkle Tree Hash with a fresh timestamp.
An STH is a "TransItem" structure of type "signed_tree_head_v2", An STH is a "TransItem" structure of type "signed_tree_head_v2",
which encapsulates a "SignedTreeHeadDataV2" structure: which encapsulates a "SignedTreeHeadDataV2" structure:
enum {
reserved(65535)
} SthExtensionType;
struct {
SthExtensionType sth_extension_type;
opaque sth_extension_data<0..2^16-1>;
} SthExtension;
struct { struct {
LogID log_id; LogID log_id;
uint64 timestamp; TreeHeadDataV2 tree_head;
uint64 tree_size;
NodeHash root_hash;
SthExtension sth_extensions<0..2^16-1>;
digitally-signed struct { digitally-signed struct {
TransItem merkle_tree_head; TreeHeadDataV2 tree_head;
} signature; } signature;
} SignedTreeHeadDataV2; } SignedTreeHeadDataV2;
"log_id" is this log's unique ID, encoded in an opaque vector as "log_id" is this log's unique ID, encoded in an opaque vector as
described in Section 5.3. described in Section 5.3.
"timestamp" is equal to the timestamp from the "TreeHeadDataV2" The "timestamp" in "tree_head" MUST be at least as recent as the most
structure encapsulated in "merkle_tree_head". This timestamp MUST be recent SCT timestamp in the tree. Each subsequent timestamp MUST be
at least as recent as the most recent SCT timestamp in the tree. more recent than the timestamp of the previous update.
Each subsequent timestamp MUST be more recent than the timestamp of
the previous update.
"tree_size" is equal to the tree size from the "TreeHeadDataV2"
structure encapsulated in "merkle_tree_head".
"root_hash" is equal to the root hash from the "TreeHeadDataV2"
structure encapsulated in "merkle_tree_head".
"sth_extension_type" identifies a single extension from the IANA
registry in Section 12.5. At the time of writing, no extensions are
specified.
The interpretation of the "sth_extension_data" field is determined
solely by the value of the "sth_extension_type" field. Each document
that registers a new "sth_extension_type" must describe how to
interpret the corresponding "sth_extension_data".
"sth_extensions" is a vector of 0 or more STH extensions. This "tree_head" contains the latest tree head information (see
vector MUST NOT include more than one extension with the same Section 5.7).
"sth_extension_type". The extensions in the vector MUST be ordered
by the value of the "sth_extension_type" field, smallest value first.
If an implementation sees an extension that it does not understand,
it SHOULD ignore that extension. Furthermore, an implementation MAY
choose to ignore any extension(s) that it does understand.
"merkle_tree_head" is a "TransItem" structure that MUST be of type "signature" is a signature over the encoded "tree_head" field.
"tree_head_v2" (see Section 5.7).
5.9. Merkle Consistency Proofs 5.9. Merkle Consistency Proofs
To prepare a Merkle Consistency Proof for distribution to clients, To prepare a Merkle Consistency Proof for distribution to clients,
the log produces a "TransItem" structure of type the log produces a "TransItem" structure of type
"consistency_proof_v2", which encapsulates a "ConsistencyProofDataV2" "consistency_proof_v2", which encapsulates a "ConsistencyProofDataV2"
structure: structure:
struct { struct {
LogID log_id; LogID log_id;
uint64 tree_size_1; uint64 tree_size_1;
uint64 tree_size_2; uint64 tree_size_2;
NodeHash consistency_path<1..2^8-1>; NodeHash consistency_path<1..2^16-1>;
} ConsistencyProofDataV2; } ConsistencyProofDataV2;
"log_id" is this log's unique ID, encoded in an opaque vector as "log_id" is this log's unique ID, encoded in an opaque vector as
described in Section 5.3. described in Section 5.3.
"tree_size_1" is the size of the older tree. "tree_size_1" is the size of the older tree.
"tree_size_2" is the size of the newer tree. "tree_size_2" is the size of the newer tree.
"consistency_path" is a vector of Merkle Tree nodes proving the "consistency_path" is a vector of Merkle Tree nodes proving the
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5.10. Merkle Inclusion Proofs 5.10. Merkle Inclusion Proofs
To prepare a Merkle Inclusion Proof for distribution to clients, the To prepare a Merkle Inclusion Proof for distribution to clients, the
log produces a "TransItem" structure of type "inclusion_proof_v2", log produces a "TransItem" structure of type "inclusion_proof_v2",
which encapsulates an "InclusionProofDataV2" structure: which encapsulates an "InclusionProofDataV2" structure:
struct { struct {
LogID log_id; LogID log_id;
uint64 tree_size; uint64 tree_size;
uint64 leaf_index; uint64 leaf_index;
NodeHash inclusion_path<1..2^8-1>; NodeHash inclusion_path<1..2^16-1>;
} InclusionProofDataV2; } InclusionProofDataV2;
"log_id" is this log's unique ID, encoded in an opaque vector as "log_id" is this log's unique ID, encoded in an opaque vector as
described in Section 5.3. described in Section 5.3.
"tree_size" is the size of the tree on which this inclusion proof is "tree_size" is the size of the tree on which this inclusion proof is
based. based.
"leaf_index" is the 0-based index of the log entry corresponding to "leaf_index" is the 0-based index of the log entry corresponding to
this inclusion proof. this inclusion proof.
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error_message: A human-readable string describing the error which error_message: A human-readable string describing the error which
prevented the log from processing the request. prevented the log from processing the request.
In the case of a malformed request, the string SHOULD provide In the case of a malformed request, the string SHOULD provide
sufficient detail for the error to be rectified. sufficient detail for the error to be rectified.
error_code: An error code readable by the client. Some codes are error_code: An error code readable by the client. 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. +---------------+---------------------------------------------+
| Error Code | Meaning |
+---------------+---------------------------------------------+
| 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
skipping to change at page 26, line 39 skipping to change at page 24, line 25
SCT; the second certifies the first and so on to the last, SCT; the second certifies the first and so on to the last,
which either is, or is certified by, an accepted trust anchor. which either is, or is certified by, an accepted trust anchor.
Outputs: Outputs:
sct: A base64 encoded "TransItem" of type "x509_sct_v2", signed sct: A base64 encoded "TransItem" of type "x509_sct_v2", signed
by this log, that corresponds to the submitted certificate. by this log, that corresponds to the submitted certificate.
Error codes: Error codes:
unknown anchor The last certificate in the chain both is not, and +-------------+-----------------------------------------------------+
is not certified by, an accepted trust anchor. | Error Code | Meaning |
+-------------+-----------------------------------------------------+
bad chain The alleged chain is not actually a chain of | unknown | The last certificate in the chain both is not, and |
certificates. | anchor | is not certified by, an accepted trust anchor. |
| | |
bad certificate One or more certificates in the chain are not | bad chain | The alleged chain is not actually a chain of |
valid (e.g. not properly encoded). | | certificates. |
| | |
shutdown The log has ceased operation and is not accepting new | bad | One or more certificates in the chain are not valid |
submissions. | certificate | (e.g., not properly encoded). |
| | |
| shutdown | The log has ceased operation and is not accepting |
| | new submissions. |
+-------------+-----------------------------------------------------+
If the version of "sct" is not v2, then a v2 client may be unable to If the version of "sct" is not v2, then a v2 client may be unable to
verify the signature. It MUST NOT construe this as an error. This verify the signature. It MUST NOT construe this as an error. This
is to avoid forcing an upgrade of compliant v2 clients that do not is to avoid forcing an upgrade of compliant v2 clients that do not
use the returned SCTs. use the returned SCTs.
If a log detects bad encoding in a chain that otherwise verifies If a log detects bad encoding in a chain that otherwise verifies
correctly then the log MUST either log the certificate or return the correctly then the log MUST either log the certificate or return the
"bad certificate" error. If the certificate is logged, an SCT MUST "bad certificate" error. If the certificate is logged, an SCT MUST
be issued. Logging the certificate is useful, because monitors be issued. Logging the certificate is useful, because monitors
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sth: A base64 encoded "TransItem" of type "signed_tree_head_v2", sth: A base64 encoded "TransItem" of type "signed_tree_head_v2",
signed by this log. signed by this log.
Note that no signature is required for the "consistency" output as Note that no signature is required for the "consistency" output as
it is used to verify the consistency between two STHs, which are it is used to verify the consistency between two STHs, which are
signed. signed.
Error codes: Error codes:
first unknown "first" is before the latest known STH but is not +-------------+-----------------------------------------------------+
from an existing STH. | Error Code | Meaning |
+-------------+-----------------------------------------------------+
second unknown "second" is before the latest known STH but is not | first | "first" is before the latest known STH but is not |
from an existing STH. | unknown | from an existing STH. |
| | |
| second | "second" is before the latest known STH but is not |
| unknown | from an existing STH. |
+-------------+-----------------------------------------------------+
See Section 10.4.2 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:
skipping to change at page 29, line 28 skipping to change at page 27, line 23
sth: A base64 encoded "TransItem" of type "signed_tree_head_v2", sth: A base64 encoded "TransItem" of type "signed_tree_head_v2",
signed by this log. signed by this log.
Note that no signature is required for the "inclusion" output as Note that no signature is required for the "inclusion" output as
it is used to verify inclusion in the selected STH, which is it is used to verify inclusion in the selected STH, which is
signed. signed.
Error codes: Error codes:
hash unknown "hash" is not the hash of a known leaf (may be +-----------+-------------------------------------------------------+
caused by skew or by a known certificate not yet merged). | Error | Meaning |
| Code | |
tree_size unknown "hash" is before the latest known STH but is +-----------+-------------------------------------------------------+
not from an existing STH. | hash | "hash" is not the hash of a known leaf (may be caused |
| unknown | by skew or by a known certificate not yet merged). |
| | |
| tree_size | "hash" is before the latest known STH but is not from |
| unknown | an existing STH. |
+-----------+-------------------------------------------------------+
See Section 10.4.1 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:
skipping to change at page 32, line 34 skipping to change at page 30, line 40
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. Optional Client Messages 7. Optional Client Messages
Logs MAY implement these messages. They are not required for correct Logs MAY implement these messages. They are not required for correct
operation of logs or their clients, but may be convenient in some operation of logs or their clients, but may be convenient in some
circumstances. Note that mirrors can implement these even if the log circumstances.
they are mirroring does not.
7.1. Get Entry Number for SCT 7.1. Get Entry Number for SCT
GET https://<log server>/ct/v2/get-entry-for-sct GET https://<log server>/ct/v2/get-entry-for-sct
Inputs: Inputs:
sct: A base64 encoded "TransItem" of type "x509_sct_v2" or sct: A base64 encoded "TransItem" of type "x509_sct_v2" or
"precert_sct_v2" signed by this log. "precert_sct_v2" signed by this log.
Outputs: Outputs:
entry: 0-based index of the log entry corresponding to the entry: 0-based index of the log entry corresponding to the
supplied SCT. supplied SCT.
Error codes: Error codes:
bad signature "sct" is not signed by this log. +-------------+-----------------------------------------------------+
| Error Code | Meaning |
not found "sct" does not correspond to an entry that is currently +-------------+-----------------------------------------------------+
available. | bad | "sct" is not signed by this log. |
| signature | |
| | |
| 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 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 log, but it may not be retrievable until the MMD has passed since
the SCT was issued. the SCT was issued.
7.2. Get Entry Numbers for Certificate 7.2. Get Entry Numbers for TBSCertificate
GET https://<log server>/ct/v2/get-entry-for-certificate GET https://<log server>/ct/v2/get-entry-for-tbscertificate
Inputs: Inputs:
hash: A base64 encoded HASH of a "TBSCertificate". Note that if hash: A base64 encoded HASH of a "TBSCertificate" for which the
the certificate has redacted labels then the "TBSCertificate" log has previously issued an SCT. (Note that a
must be constructed as described above (Section 4.2). precertificate's TBSCertificate is reconstructed from the
corresponding certificate as described in Section 10.2.2).
Outputs: Outputs:
entries: An array of 0-based indices of log entries corresponding entries: An array of 0-based indices of log entries corresponding
to the supplied HASH. to the supplied HASH.
Error codes: Error codes:
bad hash "hash" is not the right size or format. +-----------+-------------------------------------------------------+
| Error | Meaning |
not found "sct" does not correspond to an entry that is currently | Code | |
available. +-----------+-------------------------------------------------------+
| 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 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 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 index. If the certificate is present in the log, then the log MUST
return at least one entry index. return at least one entry index.
8. TLS Servers 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
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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 9.1.2). 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 which 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.
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"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".
8.4. 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 10.2.5) 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".
8.5. 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.
8.6. cached_info TLS Extension
When a TLS server includes the "transparency_info" extension in the
ServerHello, it SHOULD NOT include any "TransItem" structures of type
"x509_sct_with_proof_v2", "x509_sct_v2", "precert_sct_with_proof_v2"
or "precert_sct_v2" in the "TransItemList" if all of the following
conditions are met:
o The TLS client includes the "transparency_info" extension type in
the ClientHello.
o The TLS client includes the "cached_info" ([RFC7924]) extension
type in the ClientHello, with a "CachedObject" of type
"ct_compliant" (see Section 10.2.7) and at least one
"CachedObject" of type "cert".
o The TLS server sends a modified Certificate message (as described
in section 4.1 of [RFC7924]).
TLS servers SHOULD ignore the "hash_value" fields of each
"CachedObject" of type "ct_compliant" sent by TLS clients.
9. Certification Authorities 9. Certification Authorities
9.1. 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 9.1.1) and certificates (see included in OCSP responses (see Section 9.1.1) and certificates (see
Section 9.1.2). 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
skipping to change at page 37, line 49 skipping to change at page 36, line 47
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.
10.1. 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 12.2). Section 12.3).
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
log. A log MUST NOT use the same keypair as any other log. the 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.
Version The version of the protocol supported by the log (currently Version: The version of the protocol supported by the log (currently
1 or 2). 1 or 2).
Maximum Chain Length The longest chain submission the log is willing Maximum Chain Length: The longest chain submission the log is
to accept, if the log chose to limit it. willing to accept, if the log chose to limit it.
STH Frequency Count The maximum number of STHs the log may produce STH Frequency Count: The maximum number of STHs the log may produce
in any period equal to the "Maximum Merge Delay" (see in any period equal to the "Maximum Merge Delay" (see
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
entries), existing entries may still be valid. In this case, the new entries), existing entries may still be valid. In this case,
client should know the final valid STH in the log to ensure no new the client should know the final valid STH in the log to ensure no
entries can be added without detection. The final STH should be new entries can be added without detection. The final STH should
provided in the form of a TransItem of type signed_tree_head_v2. be provided in the form of a TransItem of type
"signed_tree_head_v2".
[JSON.Metadata] is an example of a metadata format which includes the [JSON.Metadata] is an example of a metadata format which includes the
above elements. above elements.
10.2. TLS Client 10.2. TLS Client
10.2.1. 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 8). 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.
10.2.2. 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 remove the Transparency Information
extension described in Section 9.1.
o Remove the Transparency Information extension described in
Section 9.1.
o If the redactedSubjectAltName extension (Section 4.2.2) is
present:
* TLS clients MUST verify it against the subjectAltName extension
according to Section 10.2.3.
* Once verified, remove the subjectAltName extension from the
TBSCertificate.
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).
10.2.3. Verifying the redactedSubjectAltName extension 10.2.3. Validating SCTs
If the redactedSubjectAltName extension is present, TLS clients MUST
check that the subjectAltName extension is present, that the
subjectAltName extension contains the same number of entries as the
redactedSubjectAltName extension, and that each entry in the
subjectAltName extension has a matching entry at the same position in
the redactedSubjectAltName extension. Two entries are matching if
either:
o The two entries are identical; or,
o Both entries are DNS-IDs, have the same number of labels, and each
label in the subjectAltName entry has a matching label at the same
position in the redactedSubjectAltName entry. Two labels are
matching if either:
* The two labels are identical; or,
* Neither label is "*" and the label from the
redactedSubjectAltName entry is equal to REDACT(label from
subjectAltName entry) (Section 4.2.1).
If any of these checks fail, the certificate MUST NOT be considered
compliant.
10.2.4. 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 4.2) 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.
10.2.5. 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
skipping to change at page 40, line 39 skipping to change at page 39, line 5
TLS clients SHOULD also verify each received inclusion proof (see TLS clients SHOULD also verify each received inclusion proof (see
Section 10.4.1) 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.
10.2.6. 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.
10.2.7. TLS Feature Extension A TLS client MUST NOT evaluate compliance if it did not send both the
"transparency_info" and "status_request" TLS extensions in the
ClientHello.
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 8.5) 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 8) is required. mechanisms from Section 8) is required.
10.2.7. cached_info TLS Extension
If a TLS client uses the "cached_info" TLS extension ([RFC7924]) to
indicate 1 or more cached certificates, all of which it already
considers to be CT compliant, the TLS client MAY also include a
"CachedObject" of type "ct_compliant" in the "cached_info" extension.
The "hash_value" field MUST be 1 byte long with the value 0.
10.2.8. Handling of Non-compliance 10.2.8. 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,
and the use of a compliant certificate is mandated by an explicit and the use of a compliant certificate is mandated by an explicit
security policy, application protocol specification, the TLS Feature security policy, application protocol specification, the TLS Feature
extension or any other means, the TLS client MUST refuse the extension or any other means, the TLS client MUST refuse the
connection. connection.
10.3. Monitor 10.3. Monitor
skipping to change at page 42, line 49 skipping to change at page 41, line 26
of signed proof of the log's misbehavior. of signed proof of the log's misbehavior.
A monitor (Section 10.3) 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 10.2) 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
certificate or is an appropriate name-constrained intermediate [see that certificate or is an appropriate name-constrained intermediate
Section 4.3]). (Section 4.2).
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 13.4. Section 13.3.
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.
10.4.1. 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":
skipping to change at page 43, line 38 skipping to change at page 42, line 14
If "LSB(fn)" is set, or if "fn" is equal to "sn", then: If "LSB(fn)" is set, or if "fn" is equal to "sn", then:
1. Set "r" to "HASH(0x01 || p || r)" 1. Set "r" to "HASH(0x01 || p || r)"
2. If "LSB(fn)" is not set, then right-shift both "fn" and "sn" 2. If "LSB(fn)" is not set, then right-shift both "fn" and "sn"
equally until either "LSB(fn)" is set or "fn" is "0". equally until either "LSB(fn)" is set or "fn" is "0".
Otherwise: Otherwise:
Set "r" to "HASH(0x01 || r || p)" 1. 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.
10.4.2. Verifying consistency between two STHs 10.4.2. Verifying consistency between two STHs
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If "LSB(fn)" is set, or if "fn" is equal to "sn", then: If "LSB(fn)" is set, or if "fn" is equal to "sn", then:
1. Set "fr" to "HASH(0x01 || c || fr)" 1. Set "fr" to "HASH(0x01 || c || fr)"
Set "sr" to "HASH(0x01 || c || sr)" Set "sr" to "HASH(0x01 || c || sr)"
2. If "LSB(fn)" is not set, then right-shift both "fn" and "sn" 2. If "LSB(fn)" is not set, then right-shift both "fn" and "sn"
equally until either "LSB(fn)" is set or "fn" is "0". equally until either "LSB(fn)" is set or "fn" is "0".
Otherwise: Otherwise:
Set "sr" to "HASH(0x01 || sr || c)" 1. 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.
10.4.3. Verifying root hash given entries 10.4.3. Verifying root hash given entries
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new log and the SCTs from that log used instead. new log and the SCTs from that log used instead.
12. IANA Considerations 12. IANA Considerations
12.1. 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.
12.2. Hash Algorithms 12.2. New Entry to the TLS CachedInformationType registry
IANA is asked to establish a registry of hash values, initially IANA is asked to add an entry for "ct_compliant(TBD)" to the "TLS
consisting of: CachedInformationType Values" registry that was defined in [RFC7924].
+-------+----------------------+ 12.3. Hash Algorithms
| Index | Hash |
+-------+----------------------+
| 0 | SHA-256 [FIPS.180-4] |
+-------+----------------------+
12.3. Signature Algorithms IANA is asked to establish a registry of hash algorithm values,
initially consisting of:
+-------+---------------------+
| Index | Hash |
+-------+---------------------+
| 0 | SHA-256 [FIPS180-4] |
| | |
| 255 | reserved |
+-------+---------------------+
12.4. Signature Algorithms
IANA is asked to establish a registry of signature algorithm values, IANA is asked to establish a registry of signature algorithm values,
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. |
+-------+-----------------------------------------------------------+ +-------+-----------------------------------------------------------+
12.4. SCT Extensions 12.5. 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
12.5. STH Extensions 12.6. 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
12.6. Object Identifiers 12.7. Object Identifiers
This document uses object identifiers (OIDs) to identify Log IDs (see This document uses object identifiers (OIDs) to identify Log IDs (see
Section 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
Section 4.2.2, Section 4.3 and Section 9.1.2) and OCSP responses (see and Section 9.1.2) and OCSP responses (see Section 9.1.1). The OIDs
Section 9.1.1). The OIDs are defined in an arc that was selected due are defined in an arc that was selected due to its short encoding.
to its short encoding.
12.6.1. Log ID Registry 1 12.7.1. 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"?
12.6.2. Log ID Registry 2 12.7.2. 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"?
skipping to change at page 48, line 44 skipping to change at page 47, line 21
operating correctly. Thus, the maximum period of time during which a operating correctly. Thus, the maximum period of time during which a
misissued certificate can be used without being available for audit misissued certificate can be used without being available for audit
is the MMD. is the MMD.
13.2. 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.
13.3. Avoiding Overly Redacting Domain Name Labels 13.3. Misbehaving Logs
Redaction of domain name labels carries the same risks as the use of
wildcards (See Section 7.2 of [RFC6125], for example). If the
entirety of the domain space below the unredacted part of a domain
name is not registered by a single domain owner (e.g.
"REDACT(label).com", "REDACT(label).co.uk" and other public suffixes
[Public.Suffix.List]), then the domain name may be considered by
clients to be overly redacted.
CAs should take care to avoid overly redacting domain names in
precertificates. It is expected that monitors will treat
precertificates that contain overly redacted domain names as
potentially misissued. TLS clients MAY consider a certificate to be
non-compliant if the reconstructed TBSCertificate (Section 10.2.2)
contains any overly redacted domain names.
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
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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.
13.5. Deterministic Signatures 13.4. 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.
13.6. Multiple SCTs 13.5. Multiple SCTs
By offering multiple SCTs, each from a different log, TLS servers By offering multiple SCTs, each from a different log, TLS servers
reduce the effectiveness of an attack where a CA and a log collude reduce the effectiveness of an attack where a CA and a log collude
(see Section 8.1). (see Section 8.1).
14. Privacy Considerations 14. Acknowledgements
14.1. Ensuring Effective Redaction
Although the domain name redaction mechanism (Section 4.2) removes
the need for private labels to appear in logs, it does not guarantee
that this will never happen. Anyone who encounters a certificate
could choose to submit it to one or more logs, thereby rendering the
redaction futile. Therefore, domain owners are advised to take the
following steps to minimize the likelihood that their private labels
will become known outside their closed communities:
o Avoid registering private labels in public DNS.
o Avoid using private labels that are predictable (e.g. "www").
CAs are advised to carefully consider each request to redact a label.
When a CA believes that redacting a particular label would be futile,
we advise rejecting the redaction request. TLS clients may have
policies that forbid redaction, so redaction should only be used when
it's absolutely necessary and likely to be effective.
15. Acknowledgements
The authors would like to thank Erwann Abelea, Robin Alden, Andrew The authors would like to thank Erwann Abelea, Robin Alden, Andrew
Ayer, Al Cutter, Francis Dupont, Adam Eijdenberg, Stephen Farrell, Ayer, Al Cutter, David Drysdale, Francis Dupont, Adam Eijdenberg,
Daniel Kahn Gillmor, Paul Hadfield, Brad Hill, Jeff Hodges, Paul Stephen Farrell, Daniel Kahn Gillmor, Paul Hadfield, Brad Hill, Jeff
Hoffman, Jeffrey Hutzelman, Kat Joyce, Stephen Kent, SM, Alexey Hodges, Paul Hoffman, Jeffrey Hutzelman, Kat Joyce, Stephen Kent, SM,
Melnikov, Linus Nordberg, Chris Palmer, Trevor Perrin, Pierre Alexey Melnikov, Linus Nordberg, Chris Palmer, Trevor Perrin, Pierre
Phaneuf, Melinda Shore, Ryan Sleevi, Martin Smith, Carl Wallace and Phaneuf, Melinda Shore, Ryan Sleevi, Martin Smith, Carl Wallace and
Paul Wouters for their valuable contributions. Paul Wouters for their valuable contributions.
A big thank you to Symantec for kindly donating the OIDs from the A big thank you to Symantec for kindly donating the OIDs from the
1.3.101 arc that are used in this document. 1.3.101 arc that are used in this document.
16. References 15. References
16.1. 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] [FIPS180-4]
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 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 52, line 38 skipping to change at page 50, 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>.
16.2. Informative References [RFC7924] Santesson, S. and H. Tschofenig, "Transport Layer Security
(TLS) Cached Information Extension", RFC 7924,
DOI 10.17487/RFC7924, July 2016,
<http://www.rfc-editor.org/info/rfc7924>.
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 53, line 20 skipping to change at page 51, line 25
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-03 (work in progress), July
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 and Threat Model for Certificate
Transparency", draft-ietf-trans-threat-analysis-03 (work Transparency", draft-ietf-trans-threat-analysis-08 (work
in progress), October 2015. in progress), August 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]
Mozilla Foundation, "Public Suffix List", 2016, <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 54, line 44 skipping to change at page 52, line 33
Section 3.3. of [RFC6962]. Section 3.3. of [RFC6962].
o Sign that TBSCertificate (which now contains v1 and v2 SCTs) to o Sign that TBSCertificate (which now contains v1 and v2 SCTs) to
issue the final X.509 certificate. issue the final X.509 certificate.
Authors' Addresses Authors' Addresses
Ben Laurie Ben Laurie
Google UK Ltd. Google UK Ltd.
EMail: benl@google.com Email: benl@google.com
Adam Langley Adam Langley
Google Inc. Google Inc.
EMail: agl@google.com Email: agl@google.com
Emilia Kasper Emilia Kasper
Google Switzerland GmbH Google Switzerland GmbH
EMail: ekasper@google.com Email: ekasper@google.com
Eran Messeri Eran Messeri
Google UK Ltd. Google UK Ltd.
EMail: eranm@google.com Email: eranm@google.com
Rob Stradling Rob Stradling
Comodo CA, Ltd. Comodo CA, Ltd.
EMail: rob.stradling@comodo.com Email: rob.stradling@comodo.com
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