draft-ietf-trans-rfc6962-bis-22.txt   draft-ietf-trans-rfc6962-bis-23.txt 
TRANS (Public Notary Transparency) B. Laurie TRANS (Public Notary Transparency)
Internet-Draft A. Langley Internet-Draft
Obsoletes: 6962 (if approved) E. Kasper Obsoletes: 6962 (if approved)
Intended status: Standards Track E. Messeri Intended status: Standards Track
Expires: June 17, 2017 Google Expires: June 24, 2017 Google
R. Stradling
Comodo Comodo
December 14, 2016 December 21, 2016
Certificate Transparency Version 2.0 Certificate Transparency Version 2.0
draft-ietf-trans-rfc6962-bis-22 draft-ietf-trans-rfc6962-bis-23
Abstract Abstract
This document describes version 2.0 of the Certificate Transparency This document describes version 2.0 of the Certificate Transparency
(CT) protocol for publicly logging the existence of Transport Layer (CT) protocol for publicly logging the existence of Transport Layer
Security (TLS) server certificates as they are issued or observed, in Security (TLS) server certificates as they are issued or observed, in
a manner that allows anyone to audit certification authority (CA) a manner that allows anyone to audit certification authority (CA)
activity and notice the issuance of suspect certificates as well as activity and notice the issuance of suspect certificates as well as
to audit the certificate logs themselves. The intent is that to audit the certificate logs themselves. The intent is that
eventually clients would refuse to honor certificates that do not eventually clients would refuse to honor certificates that do not
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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-
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Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
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 June 17, 2017. This Internet-Draft will expire on June 24, 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
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1.3. Major Differences from CT 1.0 . . . . . . . . . . . . . . 5 1.3. Major Differences from CT 1.0 . . . . . . . . . . . . . . 5
2. Cryptographic Components . . . . . . . . . . . . . . . . . . 7 2. Cryptographic Components . . . . . . . . . . . . . . . . . . 7
2.1. Merkle Hash Trees . . . . . . . . . . . . . . . . . . . . 7 2.1. Merkle Hash Trees . . . . . . . . . . . . . . . . . . . . 7
2.1.1. Merkle Inclusion Proofs . . . . . . . . . . . . . . . 8 2.1.1. Merkle Inclusion Proofs . . . . . . . . . . . . . . . 8
2.1.2. Merkle Consistency Proofs . . . . . . . . . . . . . . 9 2.1.2. Merkle Consistency Proofs . . . . . . . . . . . . . . 9
2.1.3. Example . . . . . . . . . . . . . . . . . . . . . . . 10 2.1.3. Example . . . . . . . . . . . . . . . . . . . . . . . 10
2.1.4. Signatures . . . . . . . . . . . . . . . . . . . . . 11 2.1.4. Signatures . . . . . . . . . . . . . . . . . . . . . 11
3. Submitters . . . . . . . . . . . . . . . . . . . . . . . . . 11 3. Submitters . . . . . . . . . . . . . . . . . . . . . . . . . 11
3.1. Certificates . . . . . . . . . . . . . . . . . . . . . . 12 3.1. Certificates . . . . . . . . . . . . . . . . . . . . . . 12
3.2. Precertificates . . . . . . . . . . . . . . . . . . . . . 12 3.2. Precertificates . . . . . . . . . . . . . . . . . . . . . 12
4. Private Domain Name Labels . . . . . . . . . . . . . . . . . 13 4. Log Format and Operation . . . . . . . . . . . . . . . . . . 13
4.1. Wildcard Certificates . . . . . . . . . . . . . . . . . . 13 4.1. Accepting Submissions . . . . . . . . . . . . . . . . . . 13
4.2. Using a Name-Constrained Intermediate CA . . . . . . . . 13 4.2. Log Entries . . . . . . . . . . . . . . . . . . . . . . . 14
5. Log Format and Operation . . . . . . . . . . . . . . . . . . 14 4.3. Log ID . . . . . . . . . . . . . . . . . . . . . . . . . 15
5.1. Accepting Submissions . . . . . . . . . . . . . . . . . . 15 4.4. TransItem Structure . . . . . . . . . . . . . . . . . . . 15
5.2. Log Entries . . . . . . . . . . . . . . . . . . . . . . . 15 4.5. Merkle Tree Leaves . . . . . . . . . . . . . . . . . . . 17
5.3. Log ID . . . . . . . . . . . . . . . . . . . . . . . . . 16 4.6. Signed Certificate Timestamp (SCT) . . . . . . . . . . . 17
5.4. TransItem Structure . . . . . . . . . . . . . . . . . . . 17 4.7. Merkle Tree Head . . . . . . . . . . . . . . . . . . . . 19
5.5. Merkle Tree Leaves . . . . . . . . . . . . . . . . . . . 18 4.8. Signed Tree Head (STH) . . . . . . . . . . . . . . . . . 20
5.6. Signed Certificate Timestamp (SCT) . . . . . . . . . . . 19 4.9. Merkle Consistency Proofs . . . . . . . . . . . . . . . . 20
5.7. Merkle Tree Head . . . . . . . . . . . . . . . . . . . . 20 4.10. Merkle Inclusion Proofs . . . . . . . . . . . . . . . . . 21
5.8. Signed Tree Head (STH) . . . . . . . . . . . . . . . . . 21 4.11. Shutting down a log . . . . . . . . . . . . . . . . . . . 21
5.9. Merkle Consistency Proofs . . . . . . . . . . . . . . . . 22 5. Log Client Messages . . . . . . . . . . . . . . . . . . . . . 22
5.10. Merkle Inclusion Proofs . . . . . . . . . . . . . . . . . 22 5.1. Add Chain to Log . . . . . . . . . . . . . . . . . . . . 24
5.11. Shutting down a log . . . . . . . . . . . . . . . . . . . 23 5.2. Add PreCertChain to Log . . . . . . . . . . . . . . . . . 25
6. Log Client Messages . . . . . . . . . . . . . . . . . . . . . 23 5.3. Retrieve Latest Signed Tree Head . . . . . . . . . . . . 25
6.1. Add Chain to Log . . . . . . . . . . . . . . . . . . . . 25 5.4. Retrieve Merkle Consistency Proof between Two Signed Tree
6.2. Add PreCertChain to Log . . . . . . . . . . . . . . . . . 26 Heads . . . . . . . . . . . . . . . . . . . . . . . . . . 25
6.3. Retrieve Latest Signed Tree Head . . . . . . . . . . . . 26
6.4. Retrieve Merkle Consistency Proof between Two Signed Tree
Heads . . . . . . . . . . . . . . . . . . . . . . . . . . 26
6.5. Retrieve Merkle Inclusion Proof from Log by Leaf Hash . . 27
6.6. Retrieve Merkle Inclusion Proof, Signed Tree Head and
Consistency Proof by Leaf Hash . . . . . . . . . . . . . 28
6.7. Retrieve Entries and STH from Log . . . . . . . . . . . . 30
6.8. Retrieve Accepted Trust Anchors . . . . . . . . . . . . . 31
7. TLS Servers . . . . . . . . . . . . . . . . . . . . . . . . . 31
7.1. Multiple SCTs . . . . . . . . . . . . . . . . . . . . . . 32
7.2. TransItemList Structure . . . . . . . . . . . . . . . . . 33
7.3. Presenting SCTs, inclusion proofs and STHs . . . . . . . 33
7.4. Presenting SCTs only . . . . . . . . . . . . . . . . . . 34
7.5. transparency_info TLS Extension . . . . . . . . . . . . . 34
7.6. cached_info TLS Extension . . . . . . . . . . . . . . . . 34
8. Certification Authorities . . . . . . . . . . . . . . . . . . 34
8.1. Transparency Information X.509v3 Extension . . . . . . . 35
8.1.1. OCSP Response Extension . . . . . . . . . . . . . . . 35
8.1.2. Certificate Extension . . . . . . . . . . . . . . . . 35
8.2. TLS Feature Extension . . . . . . . . . . . . . . . . . . 35
9. Clients . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
9.1. Metadata . . . . . . . . . . . . . . . . . . . . . . . . 36
9.2. TLS Client . . . . . . . . . . . . . . . . . . . . . . . 37
9.2.1. Receiving SCTs . . . . . . . . . . . . . . . . . . . 37
9.2.2. Reconstructing the TBSCertificate . . . . . . . . . . 37
9.2.3. Validating SCTs . . . . . . . . . . . . . . . . . . . 37
9.2.4. Validating inclusion proofs . . . . . . . . . . . . . 38
9.2.5. Evaluating compliance . . . . . . . . . . . . . . . . 38
9.2.6. TLS Feature Extension . . . . . . . . . . . . . . . . 38
9.2.7. cached_info TLS Extension . . . . . . . . . . . . . . 38
9.2.8. Handling of Non-compliance . . . . . . . . . . . . . 39
9.3. Monitor . . . . . . . . . . . . . . . . . . . . . . . . . 39
9.4. Auditing . . . . . . . . . . . . . . . . . . . . . . . . 40
9.4.1. Verifying an inclusion proof . . . . . . . . . . . . 41
9.4.2. Verifying consistency between two STHs . . . . . . . 42
9.4.3. Verifying root hash given entries . . . . . . . . . . 42
10. Algorithm Agility . . . . . . . . . . . . . . . . . . . . . . 43
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 44
11.1. TLS Extension Type . . . . . . . . . . . . . . . . . . . 44
11.2. New Entry to the TLS CachedInformationType registry . . 44
11.3. Hash Algorithms . . . . . . . . . . . . . . . . . . . . 44
11.3.1. Expert Review guidelines . . . . . . . . . . . . . . 44
11.4. Signature Algorithms . . . . . . . . . . . . . . . . . . 45
11.4.1. Expert Review guidelines . . . . . . . . . . . . . . 45
11.5. VersionedTransTypes . . . . . . . . . . . . . . . . . . 45
11.5.1. Expert Review guidelines . . . . . . . . . . . . . . 46
11.6. SCT Extensions . . . . . . . . . . . . . . . . . . . . . 47
11.6.1. Expert Review guidelines . . . . . . . . . . . . . . 47
11.7. STH Extensions . . . . . . . . . . . . . . . . . . . . . 47 5.5. Retrieve Merkle Inclusion Proof from Log by Leaf Hash . . 26
11.7.1. Expert Review guidelines . . . . . . . . . . . . . . 47 5.6. Retrieve Merkle Inclusion Proof, Signed Tree Head and
11.8. Object Identifiers . . . . . . . . . . . . . . . . . . . 48 Consistency Proof by Leaf Hash . . . . . . . . . . . . . 27
11.8.1. Log ID Registry . . . . . . . . . . . . . . . . . . 48 5.7. Retrieve Entries and STH from Log . . . . . . . . . . . . 29
11.8.2. Expert Review guidelines . . . . . . . . . . . . . . 48 5.8. Retrieve Accepted Trust Anchors . . . . . . . . . . . . . 30
12. Security Considerations . . . . . . . . . . . . . . . . . . . 49 6. TLS Servers . . . . . . . . . . . . . . . . . . . . . . . . . 30
12.1. Misissued Certificates . . . . . . . . . . . . . . . . . 49 6.1. Multiple SCTs . . . . . . . . . . . . . . . . . . . . . . 31
12.2. Detection of Misissue . . . . . . . . . . . . . . . . . 49 6.2. TransItemList Structure . . . . . . . . . . . . . . . . . 32
12.3. Misbehaving Logs . . . . . . . . . . . . . . . . . . . . 49 6.3. Presenting SCTs, inclusion proofs and STHs . . . . . . . 32
12.4. Deterministic Signatures . . . . . . . . . . . . . . . . 50 6.4. Presenting SCTs only . . . . . . . . . . . . . . . . . . 33
12.5. Multiple SCTs . . . . . . . . . . . . . . . . . . . . . 50 6.5. transparency_info TLS Extension . . . . . . . . . . . . . 33
13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 50 6.6. cached_info TLS Extension . . . . . . . . . . . . . . . . 33
14. References . . . . . . . . . . . . . . . . . . . . . . . . . 51 7. Certification Authorities . . . . . . . . . . . . . . . . . . 33
14.1. Normative References . . . . . . . . . . . . . . . . . . 51 7.1. Transparency Information X.509v3 Extension . . . . . . . 34
14.2. Informative References . . . . . . . . . . . . . . . . . 52 7.1.1. OCSP Response Extension . . . . . . . . . . . . . . . 34
Appendix A. Supporting v1 and v2 simultaneously . . . . . . . . 54 7.1.2. Certificate Extension . . . . . . . . . . . . . . . . 34
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 54 7.2. TLS Feature Extension . . . . . . . . . . . . . . . . . . 34
8. Clients . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
8.1. Metadata . . . . . . . . . . . . . . . . . . . . . . . . 35
8.2. TLS Client . . . . . . . . . . . . . . . . . . . . . . . 36
8.2.1. Receiving SCTs . . . . . . . . . . . . . . . . . . . 36
8.2.2. Reconstructing the TBSCertificate . . . . . . . . . . 36
8.2.3. Validating SCTs . . . . . . . . . . . . . . . . . . . 36
8.2.4. Validating inclusion proofs . . . . . . . . . . . . . 36
8.2.5. Evaluating compliance . . . . . . . . . . . . . . . . 37
8.2.6. TLS Feature Extension . . . . . . . . . . . . . . . . 37
8.2.7. cached_info TLS Extension . . . . . . . . . . . . . . 37
8.2.8. Handling of Non-compliance . . . . . . . . . . . . . 37
8.3. Monitor . . . . . . . . . . . . . . . . . . . . . . . . . 38
8.4. Auditing . . . . . . . . . . . . . . . . . . . . . . . . 39
8.4.1. Verifying an inclusion proof . . . . . . . . . . . . 40
8.4.2. Verifying consistency between two STHs . . . . . . . 40
8.4.3. Verifying root hash given entries . . . . . . . . . . 41
9. Algorithm Agility . . . . . . . . . . . . . . . . . . . . . . 42
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 42
10.1. TLS Extension Type . . . . . . . . . . . . . . . . . . . 42
10.2. New Entry to the TLS CachedInformationType registry . . 43
10.3. Hash Algorithms . . . . . . . . . . . . . . . . . . . . 43
10.3.1. Expert Review guidelines . . . . . . . . . . . . . . 43
10.4. Signature Algorithms . . . . . . . . . . . . . . . . . . 43
10.4.1. Expert Review guidelines . . . . . . . . . . . . . . 44
10.5. VersionedTransTypes . . . . . . . . . . . . . . . . . . 44
10.5.1. Expert Review guidelines . . . . . . . . . . . . . . 45
10.6. SCT Extensions . . . . . . . . . . . . . . . . . . . . . 46
10.6.1. Expert Review guidelines . . . . . . . . . . . . . . 46
10.7. STH Extensions . . . . . . . . . . . . . . . . . . . . . 46
10.7.1. Expert Review guidelines . . . . . . . . . . . . . . 46
10.8. Object Identifiers . . . . . . . . . . . . . . . . . . . 47
10.8.1. Log ID Registry . . . . . . . . . . . . . . . . . . 47
10.8.2. Expert Review guidelines . . . . . . . . . . . . . . 47
11. Security Considerations . . . . . . . . . . . . . . . . . . . 48
11.1. Misissued Certificates . . . . . . . . . . . . . . . . . 48
11.2. Detection of Misissue . . . . . . . . . . . . . . . . . 48
11.3. Misbehaving Logs . . . . . . . . . . . . . . . . . . . . 48
11.4. Deterministic Signatures . . . . . . . . . . . . . . . . 49
11.5. Multiple SCTs . . . . . . . . . . . . . . . . . . . . . 49
12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 49
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 50
13.1. Normative References . . . . . . . . . . . . . . . . . . 50
13.2. Informative References . . . . . . . . . . . . . . . . . 51
Appendix A. Supporting v1 and v2 simultaneously . . . . . . . . 52
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 53
1. Introduction 1. Introduction
Certificate transparency aims to mitigate the problem of misissued Certificate transparency aims to mitigate the problem of misissued
certificates by providing append-only logs of issued certificates. certificates by providing append-only logs of issued certificates.
The logs do not need to be trusted because they are publicly The logs do not need to be trusted because they are publicly
auditable. Anyone may verify the correctness of each log and monitor auditable. Anyone may verify the correctness of each log and monitor
when new certificates are added to it. The logs do not themselves when new certificates are added to it. The logs do not themselves
prevent misissue, but they ensure that interested parties prevent misissue, but they ensure that interested parties
(particularly those named in certificates) can detect such (particularly those named in certificates) can detect such
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o Precertificate format: precertificates are now CMS objects rather o Precertificate format: precertificates are now CMS objects rather
than X.509 certificates, which avoids violating the certificate than X.509 certificates, which avoids violating the certificate
serial number uniqueness requirement in Section 4.1.2.2 of serial number uniqueness requirement in Section 4.1.2.2 of
[RFC5280]. [RFC5280].
o Removed precertificate signing certificates and the precertificate o Removed precertificate signing certificates and the precertificate
poison extension: the change of precertificate format means that poison extension: the change of precertificate format means that
these are no longer needed. these are no longer needed.
o Private domain name labels: added a mechanism for logging a name-
constrained intermediate in place of end-entity certificates
issued by that CA.
o Logs IDs: each log is now identified by an OID rather than by the o Logs IDs: each log is now identified by an OID rather than by the
hash of its public key. OID allocations are managed by an IANA hash of its public key. OID allocations are managed by an IANA
registry. registry.
o "TransItem" structure: this new data structure is used to o "TransItem" structure: this new data structure is used to
encapsulate most types of CT data. A "TransItemList", consisting encapsulate most types of CT data. A "TransItemList", consisting
of one or more "TransItem" structures, can be used anywhere that of one or more "TransItem" structures, can be used anywhere that
"SignedCertificateTimestampList" was used in [RFC6962]. "SignedCertificateTimestampList" was used in [RFC6962].
o Merkle tree leaves: the "MerkleTreeLeaf" structure has been o Merkle tree leaves: the "MerkleTreeLeaf" structure has been
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leaf input entries. leaf input entries.
o Extensive clarifications and editorial work. o Extensive clarifications and editorial work.
2. Cryptographic Components 2. Cryptographic Components
2.1. Merkle Hash Trees 2.1. Merkle Hash Trees
Logs use a binary Merkle Hash Tree for efficient auditing. The 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 9.1). We have part of the metadata relating to that log (see Section 8.1). We have
established a registry of acceptable algorithms, see Section 11.3. established a registry of acceptable algorithms, see Section 10.3.
The hashing algorithm in use is referred to as HASH throughout this The hashing algorithm in use is referred to as HASH throughout this
document and the size of its output in bytes as HASH_SIZE. The input document and the size of its output in bytes as HASH_SIZE. The input
to the Merkle Tree Hash is a list of data entries; these entries will to the Merkle Tree Hash is a list of data entries; these entries will
be hashed to form the leaves of the Merkle Hash Tree. The output is be hashed to form the leaves of the Merkle Hash Tree. The output is
a single HASH_SIZE Merkle Tree Hash. Given an ordered list of n a single HASH_SIZE Merkle Tree Hash. Given an ordered list of n
inputs, D[n] = {d(0), d(1), ..., d(n-1)}, the Merkle Tree Hash (MTH) inputs, D[n] = {d(0), d(1), ..., d(n-1)}, the Merkle Tree Hash (MTH)
is thus defined as follows: 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:
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The consistency proof between hash1 and hash is PROOF(4, D[7]) = [l]. The consistency proof between hash1 and hash is PROOF(4, D[7]) = [l].
hash can be verified using hash1=k and l. hash can be verified using hash1=k and l.
The consistency proof between hash2 and hash is PROOF(6, D[7]) = [i, The consistency proof between hash2 and hash is PROOF(6, D[7]) = [i,
j, k]. k, i are used to verify hash2, and j is additionally used to j, k]. k, i are used to verify hash2, and j is additionally used to
show hash is consistent with hash2. show hash is consistent with hash2.
2.1.4. Signatures 2.1.4. Signatures
Various data structures are signed. A log MUST use one of the Various data structures are signed. A log MUST use one of the
signature algorithms defined in Section 11.4. signature algorithms defined in Section 10.4.
3. Submitters 3. Submitters
Submitters submit certificates or preannouncements of certificates Submitters submit certificates or preannouncements of certificates
prior to issuance (precertificates) to logs for public auditing, as prior to issuance (precertificates) to logs for public auditing, as
described below. In order to enable attribution of each logged described below. In order to enable attribution of each logged
certificate or precertificate to its issuer, each submission MUST be certificate or precertificate to its issuer, each submission MUST be
accompanied by all additional certificates required to verify the accompanied by all additional certificates required to verify the
chain up to an accepted trust anchor. The trust anchor (a root or chain up to an accepted trust anchor. The trust anchor (a root or
intermediate CA certificate) MAY be omitted from the submission. intermediate CA certificate) MAY be omitted from the submission.
If a log accepts a submission, it will return a Signed Certificate If a log accepts a submission, it will return a Signed Certificate
Timestamp (SCT) (see Section 5.6). The submitter SHOULD validate the Timestamp (SCT) (see Section 4.6). The submitter SHOULD validate the
returned SCT as described in Section 9.2 if they understand its returned SCT as described in Section 8.2 if they understand its
format and they intend to use it directly in a TLS handshake or to format and they intend to use it directly in a TLS handshake or to
construct a certificate. If the submitter does not need the SCT (for construct a certificate. If the submitter does not need the SCT (for
example, the certificate is being submitted simply to make it example, the certificate is being submitted simply to make it
available in the log), it MAY validate the SCT. available in the log), it MAY validate the SCT.
3.1. Certificates 3.1. Certificates
Any entity can submit a certificate (Section 6.1) to a log. Since it Any entity can submit a certificate (Section 5.1) to a log. Since it
is anticipated that TLS clients will reject certificates that are not is anticipated that TLS clients will reject certificates that are not
logged, it is expected that certificate issuers and subjects will be logged, it is expected that certificate issuers and subjects will be
strongly motivated to submit them. strongly motivated to submit them.
3.2. Precertificates 3.2. Precertificates
CAs may preannounce a certificate prior to issuance by submitting a CAs may preannounce a certificate prior to issuance by submitting a
precertificate (Section 6.2) that the log can use to create an entry precertificate (Section 5.2) 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. One example incorporate the returned SCT in the issued certificate. One example
of where the returned SCT is not incorporated in the issued of where the returned SCT is not incorporated in the issued
certificate is when a CA sends the precertificate to multiple logs, certificate is when a CA sends the precertificate to multiple logs,
but only incorporates the SCTs that are returned first. but only incorporates the SCTs that are returned first.
A precertificate is a CMS [RFC5652] "signed-data" object that A precertificate is a CMS [RFC5652] "signed-data" object that
conforms to the following requirements: conforms to the following 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 the TBSCertificate in the issued certificate, except that the
Transparency Information (Section 8.1) extension MUST be omitted. Transparency Information (Section 7.1) extension MUST be omitted.
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. Log Format and Operation
Some regard certain DNS domain name labels within their registered
domain space as private and security sensitive. Even though these
domains are often only accessible within the domain owner's private
network, it's common for them to be secured using publicly trusted
TLS server certificates.
4.1. Wildcard Certificates
A certificate containing a DNS-ID [RFC6125] of "*.example.com" could
be used to secure the domain "topsecret.example.com", without
revealing the string "topsecret" publicly.
Since TLS clients only match the wildcard character to the complete
leftmost label of the DNS domain name (see Section 6.4.3 of
[RFC6125]), a different approach is needed when any label other than
the leftmost label in a DNS-ID is considered private (e.g.,
"top.secret.example.com"). Also, wildcard certificates are
prohibited in some cases, such as Extended Validation Certificates
[EVSSLGuidelines].
4.2. Using a Name-Constrained Intermediate CA
An intermediate CA certificate or intermediate CA precertificate that
contains the Name Constraints [RFC5280] extension MAY be logged in
place of end-entity certificates issued by that intermediate CA, as
long as all of the following conditions are met:
o there MUST be a non-critical extension (OID 1.3.101.76, whose
extnValue OCTET STRING contains ASN.1 NULL data (0x05 0x00)).
This extension is an explicit indication that it is acceptable to
not log certificates issued by this intermediate CA.
o there MUST be a Name Constraints extension, in which:
* permittedSubtrees MUST specify one or more dNSNames.
* excludedSubtrees MUST specify the entire IPv4 and IPv6 address
ranges.
Below is an example Name Constraints extension that meets these
conditions:
SEQUENCE {
OBJECT IDENTIFIER '2 5 29 30'
OCTET STRING, encapsulates {
SEQUENCE {
[0] {
SEQUENCE {
[2] 'example.com'
}
}
[1] {
SEQUENCE {
[7] 00 00 00 00 00 00 00 00
}
SEQUENCE {
[7]
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
}
}
}
}
}
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 and accepts a valid submission, the log MUST return When it receives and accepts a valid submission, the log MUST return
an SCT that corresponds to the submitted certificate or an SCT that corresponds to the submitted certificate or
precertificate. If the log has previously seen this valid precertificate. If the log has previously seen this valid
submission, it SHOULD return the same SCT as it returned before (to submission, it SHOULD return the same SCT as it returned before (to
reduce the ability to track clients as described in Section 12.4). reduce the ability to track clients as described in Section 11.4).
If different SCTs are produced for the same submission, multiple log If different SCTs are produced for the same submission, multiple log
entries will have to be created, one for each SCT (as the timestamp entries will have to be created, one for each SCT (as the timestamp
is a part of the leaf structure). Note that if a certificate was is a part of the leaf structure). Note that if a certificate was
previously logged as a precertificate, then the precertificate's SCT previously logged as a precertificate, then the precertificate's SCT
of type "precert_sct_v2" would not be appropriate; instead, a fresh of type "precert_sct_v2" would not be appropriate; instead, a fresh
SCT of type "x509_sct_v2" should be generated. SCT of type "x509_sct_v2" should be generated.
An SCT is the log's promise to incorporate the submitted entry in its An SCT is the log's promise to incorporate the submitted entry in its
Merkle Tree no later than a fixed amount of time, known as the Merkle Tree no later than a fixed amount of time, known as the
Maximum Merge Delay (MMD), after the issuance of the SCT. Maximum Merge Delay (MMD), after the issuance of the SCT.
Periodically, the log MUST append all its new entries to its Merkle Periodically, the log MUST append all its new entries to its Merkle
Tree and sign the root of the tree. Tree and sign the root of the tree.
Log operators MUST NOT impose any conditions on retrieving or sharing Log operators MUST NOT impose any conditions on retrieving or sharing
data from the log. data from the log.
5.1. Accepting Submissions 4.1. Accepting Submissions
Before accepting a submitted certificate or precertificate, the log Before accepting a submitted certificate or precertificate, the log
MUST verify that it has a valid signature chain to an accepted trust MUST verify that it has a valid signature chain to an accepted trust
anchor, using the chain of intermediate CA certificates provided by anchor, using the chain of intermediate CA certificates provided by
the submitter. Logs SHOULD accept certificates and precertificates the submitter. Logs SHOULD accept certificates and precertificates
that are fully valid according to RFC 5280 [RFC5280] verification that are fully valid according to RFC 5280 [RFC5280] verification
rules and are submitted with such a chain (A log may decide, for rules and are submitted with such a chain (A log may decide, for
example, to temporarily reject valid submissions to protect itself example, to temporarily reject valid submissions to protect itself
against denial-of-service attacks). against denial-of-service attacks).
skipping to change at page 15, line 31 skipping to change at page 14, line 11
valid according to RFC 5280 verification rules in order to valid according to RFC 5280 verification rules in order to
accommodate quirks of CA certificate-issuing software. However, logs accommodate quirks of CA certificate-issuing software. However, logs
MUST reject submissions without a valid signature chain to an MUST reject submissions without a valid signature chain to an
accepted trust anchor. Logs MUST also reject precertificates that do accepted trust anchor. Logs MUST also reject precertificates that do
not conform to the requirements in Section 3.2. not conform to the requirements in Section 3.2.
Logs SHOULD limit the length of chain they will accept. The maximum Logs SHOULD limit the length of chain they will accept. The maximum
chain length is specified in the log's metadata. chain length is specified in the log's metadata.
The log SHALL allow retrieval of its list of accepted trust anchors The log SHALL allow retrieval of its list of accepted trust anchors
(see Section 6.8), each of which is a root or intermediate CA (see Section 5.8), each of which is a root or intermediate CA
certificate. This list might usefully be the union of root certificate. This list might usefully be the union of root
certificates trusted by major browser vendors. certificates trusted by major browser vendors.
5.2. Log Entries 4.2. Log Entries
If a submission is accepted and an SCT issued, the accepting log MUST If a submission is accepted and an SCT issued, the accepting log MUST
store the entire chain used for verification. This chain MUST store the entire chain used for verification. This chain MUST
include the certificate or precertificate itself, the zero or more include the certificate or precertificate itself, the zero or more
intermediate CA certificates provided by the submitter, and the trust intermediate CA certificates provided by the submitter, and the trust
anchor used to verify the chain (even if it was omitted from the anchor used to verify the chain (even if it was omitted from the
submission). The log MUST present this chain for auditing upon submission). The log MUST present this chain for auditing upon
request (see Section 6.7). This chain is required to prevent a CA request (see Section 5.7). This chain is required to prevent a CA
from avoiding blame by logging a partial or empty chain. from avoiding blame by logging a partial or empty chain.
Each certificate entry in a log MUST include a "X509ChainEntry" Each certificate entry in a log MUST include a "X509ChainEntry"
structure, and each precertificate entry MUST include a structure, and each precertificate entry MUST include a
"PrecertChainEntryV2" structure: "PrecertChainEntryV2" structure:
opaque ASN.1Cert<1..2^24-1>; opaque ASN.1Cert<1..2^24-1>;
struct { struct {
ASN.1Cert leaf_certificate; ASN.1Cert leaf_certificate;
skipping to change at page 16, line 38 skipping to change at page 15, line 16
"pre_certificate" is a submitted precertificate that has been "pre_certificate" is a submitted precertificate that has been
accepted by the log. accepted by the log.
"precertificate_chain" is a vector of 1 or more additional "precertificate_chain" is a vector of 1 or more additional
certificates required to verify "pre_certificate". The first certificates required to verify "pre_certificate". The first
certificate MUST certify "pre_certificate". Each following certificate MUST certify "pre_certificate". Each following
certificate MUST directly certify the one preceding it. The final certificate MUST directly certify the one preceding it. The final
certificate MUST be a trust anchor accepted by the log. certificate MUST be a trust anchor accepted by the log.
5.3. Log ID 4.3. 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 the Log ID Registry (see Section 11.8.1. Various data OID from the Log ID Registry (see Section 10.8.1). Various data
structures include the DER encoding of this OID, excluding the ASN.1 structures include the DER encoding of this OID, excluding the ASN.1
tag and length bytes, in an opaque vector: tag and length bytes, in an opaque vector:
opaque LogID<2..127>; opaque LogID<2..127>;
Note that the ASN.1 length and the opaque vector length are identical Note that the ASN.1 length and the opaque vector length are identical
in size (1 byte) and value, so the DER encoding of the OID can be in size (1 byte) and value, so the DER encoding of the OID can be
reproduced simply by prepending an OBJECT IDENTIFIER tag (0x06) to reproduced simply by prepending an OBJECT IDENTIFIER tag (0x06) to
the opaque vector length and contents. the opaque vector length and contents.
OIDs used to identify logs are limited such that the DER encoding of OIDs used to identify logs are limited such that the DER encoding of
their value is less than or equal to 127 octets. their value is less than or equal to 127 octets.
5.4. TransItem Structure 4.4. 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),
signed_tree_head_v2(5), consistency_proof_v2(6), signed_tree_head_v2(5), consistency_proof_v2(6),
skipping to change at page 17, line 39 skipping to change at page 16, line 30
case x509_sct_v2: SignedCertificateTimestampDataV2; case x509_sct_v2: SignedCertificateTimestampDataV2;
case precert_sct_v2: SignedCertificateTimestampDataV2; case precert_sct_v2: SignedCertificateTimestampDataV2;
case signed_tree_head_v2: SignedTreeHeadDataV2; case signed_tree_head_v2: SignedTreeHeadDataV2;
case consistency_proof_v2: ConsistencyProofDataV2; case consistency_proof_v2: ConsistencyProofDataV2;
case inclusion_proof_v2: InclusionProofDataV2; case inclusion_proof_v2: InclusionProofDataV2;
case x509_sct_with_proof_v2: SCTWithProofDataV2; case 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 a value from the IANA registry in Section 11.5 "versioned_type" is a value from the IANA registry in Section 10.5
that identifies the type of the encapsulated data structure and the that identifies the type of the encapsulated data structure and the
earliest version of this protocol to which it conforms. This earliest version of this protocol to which it conforms. This
document is v2. document is v2.
"data" is the encapsulated data structure. The various structures "data" is the encapsulated data structure. The various structures
named with the "DataV2" suffix are defined in later sections of this named with the "DataV2" suffix are defined in later sections of this
document. document.
Note that "VersionedTransType" combines the v1 [RFC6962] type Note that "VersionedTransType" combines the v1 [RFC6962] type
enumerations "Version", "LogEntryType", "SignatureType" and enumerations "Version", "LogEntryType", "SignatureType" and
"MerkleLeafType". Note also that v1 did not define "TransItem", but "MerkleLeafType". Note also that v1 did not define "TransItem", but
this document provides guidelines (see Appendix A) on how v2 this document provides guidelines (see Appendix A) on how v2
implementations can co-exist with v1 implementations. implementations can co-exist with v1 implementations.
Future versions of this protocol may reuse "VersionedTransType" Future versions of this protocol may reuse "VersionedTransType"
values defined in this document as long as the corresponding data values defined in this document as long as the corresponding data
structures are not modified, and may add new "VersionedTransType" structures are not modified, and may add new "VersionedTransType"
values for new or modified data structures. values for new or modified data structures.
5.5. Merkle Tree Leaves 4.5. Merkle Tree Leaves
The leaves of a log's Merkle Tree correspond to the log's entries The leaves of a log's Merkle Tree correspond to the log's entries
(see Section 5.2). Each leaf is the leaf hash (Section 2.1) of a (see Section 4.2). 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<32..2^8-1>; opaque issuer_key_hash<32..2^8-1>;
skipping to change at page 18, line 47 skipping to change at page 17, line 42
needed to bind the CA to the certificate or precertificate, making it needed to bind the CA to the certificate or precertificate, making it
impossible for the corresponding SCT to be valid for any other impossible for the corresponding SCT to be valid for any other
certificate or precertificate whose TBSCertificate matches certificate or precertificate whose TBSCertificate matches
"tbs_certificate". The length of the "issuer_key_hash" MUST match "tbs_certificate". The length of the "issuer_key_hash" MUST match
HASH_SIZE. HASH_SIZE.
"tbs_certificate" is the DER encoded TBSCertificate from either the "tbs_certificate" is the DER encoded TBSCertificate from either the
"leaf_certificate" (in the case of an "X509ChainEntry") or the "leaf_certificate" (in the case of an "X509ChainEntry") or the
"pre_certificate" (in the case of a "PrecertChainEntryV2"). (Note "pre_certificate" (in the case of a "PrecertChainEntryV2"). (Note
that a precertificate's TBSCertificate can be reconstructed from the that a precertificate's TBSCertificate can be reconstructed from the
corresponding certificate as described in Section 9.2.2). corresponding certificate as described in Section 8.2.2).
"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) 4.6. Signed Certificate Timestamp (SCT)
An SCT is a "TransItem" structure of type "x509_sct_v2" or An SCT is a "TransItem" structure of type "x509_sct_v2" or
"precert_sct_v2", which encapsulates a "precert_sct_v2", which encapsulates a
"SignedCertificateTimestampDataV2" structure: "SignedCertificateTimestampDataV2" structure:
enum { enum {
reserved(65535) reserved(65535)
} SctExtensionType; } SctExtensionType;
struct { struct {
skipping to change at page 19, line 30 skipping to change at page 18, line 24
struct { struct {
LogID log_id; LogID log_id;
uint64 timestamp; uint64 timestamp;
SctExtension sct_extensions<0..2^16-1>; SctExtension sct_extensions<0..2^16-1>;
digitally-signed struct { digitally-signed struct {
TransItem timestamped_entry; TransItem timestamped_entry;
} signature; } signature;
} SignedCertificateTimestampDataV2; } SignedCertificateTimestampDataV2;
"log_id" is this log's unique ID, encoded in an opaque vector as "log_id" is this log's unique ID, encoded in an opaque vector as
described in Section 5.3. described in Section 4.3.
"timestamp" is equal to the timestamp from the "timestamp" is equal to the timestamp from the
"TimestampedCertificateEntryDataV2" structure encapsulated in the "TimestampedCertificateEntryDataV2" structure encapsulated in the
"timestamped_entry". "timestamped_entry".
"sct_extension_type" identifies a single extension from the IANA "sct_extension_type" identifies a single extension from the IANA
registry in Section 11.6. At the time of writing, no extensions are registry in Section 10.6. 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
by the value of the "sct_extension_type" field, smallest value first. by the value of the "sct_extension_type" field, smallest value first.
If an implementation sees an extension that it does not understand, If an implementation sees an extension that it does not understand,
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 4.5).
5.7. Merkle Tree Head 4.7. Merkle Tree Head
The log stores information about its Merkle Tree in a The log stores information about its Merkle Tree in a
"TreeHeadDataV2": "TreeHeadDataV2":
opaque NodeHash<32..2^8-1>; opaque NodeHash<32..2^8-1>;
enum { enum {
reserved(65535) reserved(65535)
} SthExtensionType; } SthExtensionType;
skipping to change at page 20, line 36 skipping to change at page 19, line 31
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. The length of NodeHash MUST match HASH_SIZE of the log.
"sth_extension_type" identifies a single extension from the IANA "sth_extension_type" identifies a single extension from the IANA
registry in Section 11.7. At the time of writing, no extensions are registry in Section 10.7. At the time of writing, no extensions are
specified. specified.
The interpretation of the "sth_extension_data" field is determined The interpretation of the "sth_extension_data" field is determined
solely by the value of the "sth_extension_type" field. Each document solely by the value of the "sth_extension_type" field. Each document
that registers a new "sth_extension_type" must describe how to that registers a new "sth_extension_type" must describe how to
interpret the corresponding "sth_extension_data". interpret the corresponding "sth_extension_data".
"timestamp" is the current NTP Time [RFC5905], measured in "timestamp" is the current NTP Time [RFC5905], measured in
milliseconds since the epoch (January 1, 1970, 00:00 UTC), ignoring milliseconds since the epoch (January 1, 1970, 00:00 UTC), ignoring
leap seconds. leap seconds.
skipping to change at page 21, line 13 skipping to change at page 20, line 7
"root_hash" is the root of the Merkle Hash Tree. "root_hash" is the root of the Merkle Hash Tree.
"sth_extensions" is a vector of 0 or more STH extensions. This "sth_extensions" is a vector of 0 or more STH extensions. This
vector MUST NOT include more than one extension with the same vector MUST NOT include more than one extension with the same
"sth_extension_type". The extensions in the vector MUST be ordered "sth_extension_type". The extensions in the vector MUST be ordered
by the value of the "sth_extension_type" field, smallest value first. by the value of the "sth_extension_type" field, smallest value first.
If an implementation sees an extension that it does not understand, If an implementation sees an extension that it does not understand,
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.
5.8. Signed Tree Head (STH) 4.8. 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 4.7) 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 5.3), 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:
struct { struct {
LogID log_id; LogID log_id;
TreeHeadDataV2 tree_head; TreeHeadDataV2 tree_head;
digitally-signed struct { digitally-signed struct {
TreeHeadDataV2 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 4.3.
The "timestamp" in "tree_head" MUST be at least as recent as the most The "timestamp" in "tree_head" MUST be at least as recent as the most
recent SCT timestamp in the tree. Each subsequent timestamp MUST be recent SCT timestamp in the tree. Each subsequent timestamp MUST be
more recent than the timestamp of the previous update. more recent than the timestamp of the previous update.
"tree_head" contains the latest tree head information (see "tree_head" contains the latest tree head information (see
Section 5.7). Section 4.7).
"signature" is a signature over the encoded "tree_head" field. "signature" is a signature over the encoded "tree_head" field.
5.9. Merkle Consistency Proofs 4.9. 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..2^16-1>; NodeHash consistency_path<1..2^16-1>;
} ConsistencyProofDataV2; } ConsistencyProofDataV2;
"log_id" is this log's unique ID, encoded in an opaque vector as "log_id" is this log's unique ID, encoded in an opaque vector as
described in Section 5.3. described in Section 4.3.
"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
consistency of two STHs. consistency of two STHs.
5.10. Merkle Inclusion Proofs 4.10. 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..2^16-1>; NodeHash inclusion_path<1..2^16-1>;
} InclusionProofDataV2; } InclusionProofDataV2;
"log_id" is this log's unique ID, encoded in an opaque vector as "log_id" is this log's unique ID, encoded in an opaque vector as
described in Section 5.3. described in Section 4.3.
"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.
"inclusion_path" is a vector of Merkle Tree nodes proving the "inclusion_path" is a vector of Merkle Tree nodes proving the
inclusion of the chosen certificate or precertificate. inclusion of the chosen certificate or precertificate.
5.11. Shutting down a log 4.11. Shutting down a log
Log operators may decide to shut down a log for various reasons, such Log operators may decide to shut down a log for various reasons, such
as deprecation of the signature algorithm. If there are entries in as deprecation of the signature algorithm. If there are entries in
the log for certificates that have not yet expired, simply making TLS the log for certificates that have not yet expired, simply making TLS
clients stop recognizing that log will have the effect of clients stop recognizing that log will have the effect of
invalidating SCTs from that log. To avoid that, the following invalidating SCTs from that log. To avoid that, the following
actions are suggested: actions are suggested:
o Make it known to clients and monitors that the log will be frozen. o Make it known to clients and monitors that the log will be frozen.
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timestamp that is after the MMD has passed from the last SCT timestamp that is after the MMD has passed from the last SCT
issuance allows clients to audit this log regularly without issuance allows clients to audit this log regularly without
special handling for the final STH. At this point the log's special handling for the final STH. At this point the log's
private key is no longer needed and can be destroyed. private key is no longer needed and can be destroyed.
o Keep the log running until the certificates in all of its entries o Keep the log running until the certificates in all of its entries
have expired or exist in other logs (this can be determined by have expired or exist in other logs (this can be determined by
scanning other logs or connecting to domains mentioned in the scanning other logs or connecting to domains mentioned in the
certificates and inspecting the SCTs served). certificates and inspecting the SCTs served).
6. Log Client Messages 5. Log Client Messages
Messages are sent as HTTPS GET or POST requests. Parameters for Messages are sent as HTTPS GET or POST requests. Parameters for
POSTs and all responses are encoded as JavaScript Object Notation POSTs and all responses are encoded as JavaScript Object Notation
(JSON) objects [RFC7159]. Parameters for GETs are encoded as order- (JSON) objects [RFC7159]. Parameters for GETs are encoded as order-
independent key/value URL parameters, using the "application/x-www- independent key/value URL parameters, using the "application/x-www-
form-urlencoded" format described in the "HTML 4.01 Specification" form-urlencoded" format described in the "HTML 4.01 Specification"
[HTML401]. Binary data is base64 encoded [RFC4648] as specified in [HTML401]. Binary data is base64 encoded [RFC4648] as specified in
the individual messages. the individual messages.
Note that JSON objects and URL parameters may contain fields not Note that JSON objects and URL parameters may contain fields not
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"error_code": "not compliant", "error_code": "not compliant",
} }
Clients SHOULD treat "500 Internal Server Error" and "503 Service Clients SHOULD treat "500 Internal Server Error" and "503 Service
Unavailable" responses as transient failures and MAY retry the same Unavailable" responses as transient failures and MAY retry the same
request without modification at a later date. Note that as per request without modification at a later date. Note that as per
[RFC7231], in the case of a 503 response the log MAY include a [RFC7231], in the case of a 503 response the log MAY include a
"Retry-After:" header in order to request a minimum time for the "Retry-After:" header in order to request a minimum time for the
client to wait before retrying the request. client to wait before retrying the request.
6.1. Add Chain to Log 5.1. Add Chain to Log
POST https://<log server>/ct/v2/add-chain POST https://<log server>/ct/v2/add-chain
Inputs: Inputs:
chain: An array of base64 encoded certificates. The first chain: An array of base64 encoded certificates. The first
element is the certificate for which the submitter desires an element is the certificate for which the submitter desires an
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.
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If the version of "sct" is not v2, then a v2 client may be unable to If the version of "sct" is not v2, then a v2 client may be unable to
verify the signature. It MUST NOT construe this as an error. This verify the signature. It MUST NOT construe this as an error. This
is to avoid forcing an upgrade of compliant v2 clients that do not is to avoid forcing an upgrade of compliant v2 clients that do not
use the returned SCTs. use the returned SCTs.
If a log detects bad encoding in a chain that otherwise verifies If a log detects bad encoding in a chain that otherwise verifies
correctly then the log MUST either log the certificate or return the correctly then the log MUST either log the certificate or return the
"bad certificate" error. If the certificate is logged, an SCT MUST "bad certificate" error. If the certificate is logged, an SCT MUST
be issued. Logging the certificate is useful, because monitors be issued. Logging the certificate is useful, because monitors
(Section 9.3) can then detect these encoding errors, which may be (Section 8.3) can then detect these encoding errors, which may be
accepted by some TLS clients. accepted by some TLS clients.
6.2. Add PreCertChain to Log 5.2. Add PreCertChain to Log
POST https://<log server>/ct/v2/add-pre-chain POST https://<log server>/ct/v2/add-pre-chain
Inputs: Inputs:
precertificate: The base64 encoded precertificate. precertificate: The base64 encoded precertificate.
chain: An array of base64 encoded CA certificates. The first chain: An array of base64 encoded CA certificates. The first
element is the signer of the precertificate; the second element is the signer of the precertificate; the second
certifies the first and so on to the last, which either is, or certifies the first and so on to the last, which either is, or
is certified by, an accepted trust anchor. is certified by, an accepted trust anchor.
Outputs: Outputs:
sct: A base64 encoded "TransItem" of type "precert_sct_v2", sct: A base64 encoded "TransItem" of type "precert_sct_v2",
signed by this log, that corresponds to the submitted signed by this log, that corresponds to the submitted
precertificate. precertificate.
Errors are the same as in Section 6.1. Errors are the same as in Section 5.1.
6.3. Retrieve Latest Signed Tree Head 5.3. Retrieve Latest Signed Tree Head
GET https://<log server>/ct/v2/get-sth GET https://<log server>/ct/v2/get-sth
No inputs. No inputs.
Outputs: Outputs:
sth: A base64 encoded "TransItem" of type "signed_tree_head_v2", sth: A base64 encoded "TransItem" of type "signed_tree_head_v2",
signed by this log, that is no older than the log's MMD. signed by this log, that is no older than the log's MMD.
6.4. Retrieve Merkle Consistency Proof between Two Signed Tree Heads 5.4. Retrieve Merkle Consistency Proof between Two Signed Tree Heads
GET https://<log server>/ct/v2/get-sth-consistency GET https://<log server>/ct/v2/get-sth-consistency
Inputs: Inputs:
first: The tree_size of the older tree, in decimal. first: The tree_size of the older tree, in decimal.
second: The tree_size of the newer tree, in decimal (optional). second: The tree_size of the newer tree, in decimal (optional).
Both tree sizes must be from existing v2 STHs. However, because Both tree sizes must be from existing v2 STHs. However, because
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+-------------+-----------------------------------------------------+ +-------------+-----------------------------------------------------+
| Error Code | Meaning | | Error Code | Meaning |
+-------------+-----------------------------------------------------+ +-------------+-----------------------------------------------------+
| first | "first" is before the latest known STH but is not | | first | "first" is before the latest known STH but is not |
| unknown | from an existing STH. | | unknown | from an existing STH. |
| | | | | |
| second | "second" is before the latest known STH but is not | | second | "second" is before the latest known STH but is not |
| unknown | from an existing STH. | | unknown | from an existing STH. |
+-------------+-----------------------------------------------------+ +-------------+-----------------------------------------------------+
See Section 9.4.2 for an outline of how to use the "consistency" See Section 8.4.2 for an outline of how to use the "consistency"
output. output.
6.5. Retrieve Merkle Inclusion Proof from Log by Leaf Hash 5.5. Retrieve Merkle Inclusion Proof from Log by Leaf Hash
GET https://<log server>/ct/v2/get-proof-by-hash GET https://<log server>/ct/v2/get-proof-by-hash
Inputs: Inputs:
hash: A base64 encoded v2 leaf hash. hash: A base64 encoded v2 leaf hash.
tree_size: The tree_size of the tree on which to base the proof, tree_size: The tree_size of the tree on which to base the proof,
in decimal. in decimal.
The "hash" must be calculated as defined in Section 5.5. The The "hash" must be calculated as defined in Section 4.5. The
"tree_size" must designate an existing v2 STH. Because of skew, "tree_size" must designate an existing v2 STH. Because of skew,
the front-end may not know the requested STH. In that case, it the front-end may not know the requested STH. In that case, it
will return the latest STH it knows, along with an inclusion proof will return the latest STH it knows, along with an inclusion proof
to that STH. If the front-end knows the requested STH then only to that STH. If the front-end knows the requested STH then only
"inclusion" is returned. "inclusion" is returned.
Outputs: Outputs:
inclusion: A base64 encoded "TransItem" of type inclusion: A base64 encoded "TransItem" of type
"inclusion_proof_v2" whose "inclusion_path" array of Merkle "inclusion_proof_v2" whose "inclusion_path" array of Merkle
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| Error | Meaning | | Error | Meaning |
| Code | | | Code | |
+-----------+-------------------------------------------------------+ +-----------+-------------------------------------------------------+
| hash | "hash" is not the hash of a known leaf (may be caused | | hash | "hash" is not the hash of a known leaf (may be caused |
| unknown | by skew or by a known certificate not yet merged). | | unknown | by skew or by a known certificate not yet merged). |
| | | | | |
| tree_size | "hash" is before the latest known STH but is not from | | tree_size | "hash" is before the latest known STH but is not from |
| unknown | an existing STH. | | unknown | an existing STH. |
+-----------+-------------------------------------------------------+ +-----------+-------------------------------------------------------+
See Section 9.4.1 for an outline of how to use the "inclusion" See Section 8.4.1 for an outline of how to use the "inclusion"
output. output.
6.6. Retrieve Merkle Inclusion Proof, Signed Tree Head and Consistency 5.6. Retrieve Merkle Inclusion Proof, Signed Tree Head and Consistency
Proof by Leaf Hash Proof by Leaf Hash
GET https://<log server>/ct/v2/get-all-by-hash GET https://<log server>/ct/v2/get-all-by-hash
Inputs: Inputs:
hash: A base64 encoded v2 leaf hash. hash: A base64 encoded v2 leaf hash.
tree_size: The tree_size of the tree on which to base the proofs, tree_size: The tree_size of the tree on which to base the proofs,
in decimal. in decimal.
The "hash" must be calculated as defined in Section 5.5. The The "hash" must be calculated as defined in Section 4.5. The
"tree_size" must designate an existing v2 STH. "tree_size" must designate an existing v2 STH.
Because of skew, the front-end may not know the requested STH or Because of skew, the front-end may not know the requested STH or
the requested hash, which leads to a number of cases. the requested hash, which leads to a number of cases.
latest STH < requested STH Return latest STH. latest STH < requested STH Return latest STH.
latest STH > requested STH Return latest STH and a consistency latest STH > requested STH Return latest STH and a consistency
proof between it and the requested STH (see Section 6.4). proof between it and the requested STH (see Section 5.4).
index of requested hash < latest STH Return "inclusion". index of requested hash < latest STH Return "inclusion".
Note that more than one case can be true, in which case the Note that more than one case can be true, in which case the
returned data is their concatenation. It is also possible for returned data is their concatenation. It is also possible for
none to be true, in which case the front-end MUST return an empty none to be true, in which case the front-end MUST return an empty
response. response.
Outputs: Outputs:
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signed by this log. signed by this log.
consistency: A base64 encoded "TransItem" of type consistency: A base64 encoded "TransItem" of type
"consistency_proof_v2" that proves the consistency of the "consistency_proof_v2" that proves the consistency of the
requested STH and the returned STH. requested STH and the returned STH.
Note that no signature is required for the "inclusion" or Note that no signature is required for the "inclusion" or
"consistency" outputs as they are used to verify inclusion in and "consistency" outputs as they are used to verify inclusion in and
consistency of STHs, which are signed. consistency of STHs, which are signed.
Errors are the same as in Section 6.5. Errors are the same as in Section 5.5.
See Section 9.4.1 for an outline of how to use the "inclusion" See Section 8.4.1 for an outline of how to use the "inclusion"
output, and see Section 9.4.2 for an outline of how to use the output, and see Section 8.4.2 for an outline of how to use the
"consistency" output. "consistency" output.
6.7. Retrieve Entries and STH from Log 5.7. Retrieve Entries and STH from Log
GET https://<log server>/ct/v2/get-entries GET https://<log server>/ct/v2/get-entries
Inputs: Inputs:
start: 0-based index of first entry to retrieve, in decimal. start: 0-based index of first entry to retrieve, in decimal.
end: 0-based index of last entry to retrieve, in decimal. end: 0-based index of last entry to retrieve, in decimal.
Outputs: Outputs:
entries: An array of objects, each consisting of entries: An array of objects, each consisting of
leaf_input: The base64 encoded "TransItem" structure of type leaf_input: The base64 encoded "TransItem" structure of type
"x509_entry_v2" or "precert_entry_v2" (see Section 5.5). "x509_entry_v2" or "precert_entry_v2" (see Section 4.5).
log_entry: The base64 encoded log entry (see Section 5.2). In log_entry: The base64 encoded log entry (see Section 4.2). In
the case of an "x509_entry_v2" entry, this is the whole the case of an "x509_entry_v2" entry, this is the whole
"X509ChainEntry"; and in the case of a "precert_entry_v2", "X509ChainEntry"; and in the case of a "precert_entry_v2",
this is the whole "PrecertChainEntryV2". this is the whole "PrecertChainEntryV2".
sct: The base64 encoded "TransItem" of type "x509_sct_v2" or sct: The base64 encoded "TransItem" of type "x509_sct_v2" or
"precert_sct_v2" corresponding to this log entry. "precert_sct_v2" corresponding to this log entry.
sth: A base64 encoded "TransItem" of type "signed_tree_head_v2", sth: A base64 encoded "TransItem" of type "signed_tree_head_v2",
signed by this log. signed by this log.
Note that this message is not signed -- the "entries" data can be Note that this message is not signed -- the "entries" data can be
verified by constructing the Merkle Tree Hash corresponding to a verified by constructing the Merkle Tree Hash corresponding to a
retrieved STH. All leaves MUST be v2. However, a compliant v2 retrieved STH. All leaves MUST be v2. However, a compliant v2
client MUST NOT construe an unrecognized TransItem type as an error. client MUST NOT construe an unrecognized TransItem type as an error.
This means it may be unable to parse some entries, but note that each This means it may be unable to parse some entries, but note that each
client can inspect the entries it does recognize as well as verify client can inspect the entries it does recognize as well as verify
the integrity of the data by treating unrecognized leaves as opaque the integrity of the data by treating unrecognized leaves as opaque
input to the tree. input to the tree.
The "start" and "end" parameters SHOULD be within the range 0 <= x < The "start" and "end" parameters SHOULD be within the range 0 <= x <
"tree_size" as returned by "get-sth" in Section 6.3. "tree_size" as returned by "get-sth" in Section 5.3.
The "start" parameter MUST be less than or equal to the "end" The "start" parameter MUST be less than or equal to the "end"
parameter. parameter.
Log servers MUST honor requests where 0 <= "start" < "tree_size" and Log servers MUST honor requests where 0 <= "start" < "tree_size" and
"end" >= "tree_size" by returning a partial response covering only "end" >= "tree_size" by returning a partial response covering only
the valid entries in the specified range. "end" >= "tree_size" could the valid entries in the specified range. "end" >= "tree_size" could
be caused by skew. Note that the following restriction may also be caused by skew. Note that the following restriction may also
apply: apply:
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permissible. These entries SHALL be sequential beginning with the permissible. These entries SHALL be sequential beginning with the
entry specified by "start". entry specified by "start".
Because of skew, it is possible the log server will not have any Because of skew, it is possible the log server will not have any
entries between "start" and "end". In this case it MUST return an entries between "start" and "end". In this case it MUST return an
empty "entries" array. empty "entries" array.
In any case, the log server MUST return the latest STH it knows In any case, the log server MUST return the latest STH it knows
about. about.
See Section 9.4.3 for an outline of how to use a complete list of See Section 8.4.3 for an outline of how to use a complete list of
"leaf_input" entries to verify the "root_hash". "leaf_input" entries to verify the "root_hash".
6.8. Retrieve Accepted Trust Anchors 5.8. Retrieve Accepted Trust Anchors
GET https://<log server>/ct/v2/get-anchors GET https://<log server>/ct/v2/get-anchors
No inputs. No inputs.
Outputs: Outputs:
certificates: An array of base64 encoded trust anchors that are certificates: An array of base64 encoded trust anchors that are
acceptable to the log. acceptable to the log.
max_chain: If the server has chosen to limit the length of chains max_chain: If the server has chosen to limit the length of chains
it accepts, this is the maximum number of certificates in the it accepts, this is the maximum number of certificates in the
chain, in decimal. If there is no limit, this is omitted. chain, in decimal. If there is no limit, this is omitted.
7. TLS Servers 6. TLS Servers
TLS servers MUST use at least one of the three mechanisms listed TLS servers MUST use at least one of the three mechanisms listed
below to present one or more SCTs from one or more logs to each TLS below to present one or more SCTs from one or more logs to each TLS
client during full TLS handshakes, where each SCT corresponds to the client during full TLS handshakes, where each SCT corresponds to the
server certificate or to a name-constrained intermediate the server server certificate. TLS servers SHOULD also present corresponding
certificate chains to. TLS servers SHOULD also present corresponding inclusion proofs and STHs (see Section 6.3).
inclusion proofs and STHs (see Section 7.3).
Three mechanisms are provided because they have different tradeoffs. Three mechanisms are provided because they have different tradeoffs.
o A TLS extension (Section 7.4.1.4 of [RFC5246]) with type o A TLS extension (Section 7.4.1.4 of [RFC5246]) with type
"transparency_info" (see Section 7.5). This mechanism allows TLS "transparency_info" (see Section 6.5). This mechanism allows TLS
servers to participate in CT without the cooperation of CAs, servers to participate in CT without the cooperation of CAs,
unlike the other two mechanisms. It also allows SCTs and unlike the other two mechanisms. It also allows SCTs and
inclusion proofs to be updated on the fly. inclusion proofs to be updated on the fly.
o An Online Certificate Status Protocol (OCSP) [RFC6960] response o An Online Certificate Status Protocol (OCSP) [RFC6960] response
extension (see Section 8.1.1), where the OCSP response is provided extension (see Section 7.1.1), where the OCSP response is provided
in the "CertificateStatus" message, provided that the TLS client in the "CertificateStatus" message, provided that the TLS client
included the "status_request" extension in the (extended) included the "status_request" extension in the (extended)
"ClientHello" (Section 8 of [RFC6066]). This mechanism, popularly "ClientHello" (Section 8 of [RFC6066]). This mechanism, popularly
known as OCSP stapling, is already widely (but not universally) known as OCSP stapling, is already widely (but not universally)
implemented. It also allows SCTs and inclusion proofs to be implemented. It also allows SCTs and inclusion proofs to be
updated on the fly. updated on the fly.
o An X509v3 certificate extension (see Section 8.1.2). This o An X509v3 certificate extension (see Section 7.1.2). 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 which 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.
7.1. Multiple SCTs 6.1. Multiple SCTs
TLS servers SHOULD send SCTs from multiple logs in case one or more TLS servers SHOULD send SCTs from multiple logs in case one or more
logs are not acceptable to the TLS client (for example, if a log has logs are not acceptable to the TLS client (for example, if a log has
been struck off for misbehavior, has had a key compromise, or is not been struck off for misbehavior, has had a key compromise, or is not
known to the TLS client). For example: known to the TLS client). For example:
o If a CA and a log collude, it is possible to temporarily hide o If a CA and a log collude, it is possible to temporarily hide
misissuance from clients. Including SCTs from different logs misissuance from clients. Including SCTs from different logs
makes it more difficult to mount this attack. makes it more difficult to mount this attack.
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o TLS clients may have policies related to the above risks requiring o TLS clients may have policies related to the above risks requiring
servers to present multiple SCTs. For example, at the time of servers to present multiple SCTs. For example, at the time of
writing, Chromium [Chromium.Log.Policy] requires multiple SCTs to writing, Chromium [Chromium.Log.Policy] requires multiple SCTs to
be presented with EV certificates in order for the EV indicator to be presented with EV certificates in order for the EV indicator to
be shown. be shown.
To select the logs from which to obtain SCTs, a TLS server can, for To select the logs from which to obtain SCTs, a TLS server can, for
example, examine the set of logs popular TLS clients accept and example, examine the set of logs popular TLS clients accept and
recognize. recognize.
7.2. TransItemList Structure 6.2. TransItemList Structure
Multiple SCTs, inclusion proofs, and indeed "TransItem" structures of Multiple SCTs, inclusion proofs, and indeed "TransItem" structures of
any type, are combined into a list as follows: any type, are combined into a list as follows:
opaque SerializedTransItem<1..2^16-1>; opaque SerializedTransItem<1..2^16-1>;
struct { struct {
SerializedTransItem trans_item_list<1..2^16-1>; SerializedTransItem trans_item_list<1..2^16-1>;
} TransItemList; } TransItemList;
Here, "SerializedTransItem" is an opaque byte string that contains Here, "SerializedTransItem" is an opaque byte string that contains
the serialized "TransItem" structure. This encoding ensures that TLS the serialized "TransItem" structure. This encoding ensures that TLS
clients can decode each "TransItem" individually (so, for example, if clients can decode each "TransItem" individually (so, for example, if
there is a version upgrade, out-of-date clients can still parse old there is a version upgrade, out-of-date clients can still parse old
"TransItem" structures while skipping over new "TransItem" structures "TransItem" structures while skipping over new "TransItem" structures
whose versions they don't understand). whose versions they don't understand).
7.3. Presenting SCTs, inclusion proofs and STHs 6.3. Presenting SCTs, inclusion proofs and STHs
When constructing a "TransItemList" structure, a TLS server SHOULD When constructing a "TransItemList" structure, a TLS server SHOULD
construct and include "TransItem" structures of type construct and include "TransItem" structures of type
"x509_sct_with_proof_v2" (for an SCT of type "x509_sct_v2") or "x509_sct_with_proof_v2" (for an SCT of type "x509_sct_v2") or
"precert_sct_with_proof_v2" (for an SCT of type "precert_sct_v2"), "precert_sct_with_proof_v2" (for an SCT of type "precert_sct_v2"),
both of which encapsulate a "SCTWithProofDataV2" structure: both of which encapsulate a "SCTWithProofDataV2" structure:
struct { struct {
SignedCertificateTimestampDataV2 sct; SignedCertificateTimestampDataV2 sct;
SignedTreeHeadDataV2 sth; SignedTreeHeadDataV2 sth;
InclusionProofDataV2 inclusion_proof; InclusionProofDataV2 inclusion_proof;
} SCTWithProofDataV2; } SCTWithProofDataV2;
"sct" is the encapsulated data structure from an SCT that corresponds "sct" is the encapsulated data structure from an SCT that corresponds
to the server certificate or to a name-constrained intermediate the to the server certificate.
server certificate chains to.
"sth" is the encapsulated data structure from an STH that was signed "sth" is the encapsulated data structure from an STH that was signed
by the same log as "sct". by the same log as "sct".
"inclusion_proof" is the encapsulated data structure from an "inclusion_proof" is the encapsulated data structure from an
inclusion proof that corresponds to "sct" and can be used to compute inclusion proof that corresponds to "sct" and can be used to compute
the root in "sth". the root in "sth".
7.4. Presenting SCTs only 6.4. Presenting SCTs only
Presenting inclusion proofs and STHs in the TLS handshake helps to Presenting inclusion proofs and STHs in the TLS handshake helps to
protect the client's privacy (see Section 9.2.4) and reduces load on protect the client's privacy (see Section 8.2.4) and reduces load on
log servers. However, if a TLS server is unable to obtain an log servers. However, if a TLS server is unable to obtain an
inclusion proof and STH that correspond to an SCT, then it MUST inclusion proof and STH that correspond to an SCT, then it MUST
include "TransItem" structures of type "x509_sct_v2" or include "TransItem" structures of type "x509_sct_v2" or
"precert_sct_v2" in the "TransItemList". "precert_sct_v2" in the "TransItemList".
7.5. transparency_info TLS Extension 6.5. 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.
7.6. cached_info TLS Extension 6.6. cached_info TLS Extension
When a TLS server includes the "transparency_info" extension in the When a TLS server includes the "transparency_info" extension in the
ServerHello, it SHOULD NOT include any "TransItem" structures of type ServerHello, it SHOULD NOT include any "TransItem" structures of type
"x509_sct_with_proof_v2", "x509_sct_v2", "precert_sct_with_proof_v2" "x509_sct_with_proof_v2", "x509_sct_v2", "precert_sct_with_proof_v2"
or "precert_sct_v2" in the "TransItemList" if all of the following or "precert_sct_v2" in the "TransItemList" if all of the following
conditions are met: conditions are met:
o The TLS client includes the "transparency_info" extension type in o The TLS client includes the "transparency_info" extension type in
the ClientHello. the ClientHello.
o The TLS client includes the "cached_info" ([RFC7924]) extension o The TLS client includes the "cached_info" ([RFC7924]) extension
type in the ClientHello, with a "CachedObject" of type type in the ClientHello, with a "CachedObject" of type
"ct_compliant" (see Section 9.2.7) and at least one "CachedObject" "ct_compliant" (see Section 8.2.7) and at least one "CachedObject"
of type "cert". of type "cert".
o The TLS server sends a modified Certificate message (as described o The TLS server sends a modified Certificate message (as described
in section 4.1 of [RFC7924]). in section 4.1 of [RFC7924]).
TLS servers SHOULD ignore the "hash_value" fields of each TLS servers SHOULD ignore the "hash_value" fields of each
"CachedObject" of type "ct_compliant" sent by TLS clients. "CachedObject" of type "ct_compliant" sent by TLS clients.
8. Certification Authorities 7. Certification Authorities
8.1. Transparency Information X.509v3 Extension 7.1. Transparency Information X.509v3 Extension
The Transparency Information X.509v3 extension, which has OID The Transparency Information X.509v3 extension, which has OID
1.3.101.75 and SHOULD be non-critical, contains one or more 1.3.101.75 and SHOULD be non-critical, contains one or more
"TransItem" structures in a "TransItemList". This extension MAY be "TransItem" structures in a "TransItemList". This extension MAY be
included in OCSP responses (see Section 8.1.1) and certificates (see included in OCSP responses (see Section 7.1.1) and certificates (see
Section 8.1.2). Since RFC5280 requires the "extnValue" field (an Section 7.1.2). Since RFC5280 requires the "extnValue" field (an
OCTET STRING) of each X.509v3 extension to include the DER encoding OCTET STRING) of each X.509v3 extension to include the DER encoding
of an ASN.1 value, a "TransItemList" MUST NOT be included directly. of an ASN.1 value, a "TransItemList" MUST NOT be included directly.
Instead, it MUST be wrapped inside an additional OCTET STRING, which Instead, it MUST be wrapped inside an additional OCTET STRING, which
is then put into the "extnValue" field: is then put into the "extnValue" field:
TransparencyInformationSyntax ::= OCTET STRING TransparencyInformationSyntax ::= OCTET STRING
"TransparencyInformationSyntax" contains a "TransItemList". "TransparencyInformationSyntax" contains a "TransItemList".
8.1.1. OCSP Response Extension 7.1.1. OCSP Response Extension
A certification authority MAY include a Transparency Information A certification authority MAY include a Transparency Information
X.509v3 extension in the "singleExtensions" of a "SingleResponse" in X.509v3 extension in the "singleExtensions" of a "SingleResponse" in
an OCSP response. The included SCTs or inclusion proofs MUST be for an OCSP response. The included SCTs or inclusion proofs MUST be for
the certificate identified by the "certID" of that "SingleResponse", the certificate identified by the "certID" of that "SingleResponse",
or for a precertificate that corresponds to that certificate, or for or for a precertificate that corresponds to that certificate.
a name-constrained intermediate to which that certificate chains.
8.1.2. Certificate Extension 7.1.2. Certificate Extension
A certification authority MAY include a Transparency Information A certification authority MAY include a Transparency Information
X.509v3 extension in a certificate. Any included SCTs or inclusion X.509v3 extension in a certificate. Any included SCTs or inclusion
proofs MUST be either for a precertificate that corresponds to this proofs MUST be for a precertificate that corresponds to this
certificate, or for a name-constrained intermediate to which this certificate.
certificate chains.
8.2. TLS Feature Extension 7.2. TLS Feature Extension
A certification authority MAY include the transparency_info A certification authority MAY include the transparency_info
(Section 7.5) TLS extension identifier in the TLS Feature [RFC7633] (Section 6.5) TLS extension identifier in the TLS Feature [RFC7633]
certificate extension in root, intermediate and end-entity certificate extension in root, intermediate and end-entity
certificates. When a certificate chain includes such a certificate, certificates. When a certificate chain includes such a certificate,
this indicates that CT compliance is required. this indicates that CT compliance is required.
9. Clients 8. Clients
There are various different functions clients of logs might perform. There are various different functions clients of logs might perform.
We describe here some typical clients and how they should function. We describe here some typical clients and how they should function.
Any inconsistency may be used as evidence that a log has not behaved Any inconsistency may be used as evidence that a log has not behaved
correctly, and the signatures on the data structures prevent the log correctly, and the signatures on the data structures prevent the log
from denying that misbehavior. from denying that misbehavior.
All clients need various metadata in order to communicate with logs All clients need various metadata in order to communicate with logs
and verify their responses. This metadata is described below, but and verify their responses. This metadata is described below, but
note that this document does not describe how the metadata is note that this document does not describe how the metadata is
obtained, which is implementation dependent (see, for example, obtained, which is implementation dependent (see, for example,
[Chromium.Policy]). [Chromium.Policy]).
Clients should somehow exchange STHs they see, or make them available Clients should somehow exchange STHs they see, or make them available
for scrutiny, in order to ensure that they all have a consistent for scrutiny, in order to ensure that they all have a consistent
view. The exact mechanisms will be in separate documents, but it is view. The exact mechanisms will be in separate documents, but it is
expected there will be a variety. expected there will be a variety.
9.1. Metadata 8.1. 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 5.
Hash Algorithm: The hash algorithm used for the Merkle Tree (see Hash Algorithm: The hash algorithm used for the Merkle Tree (see
Section 11.3). Section 10.3).
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 Public Key: The public key used to verify signatures generated by
the log. A log MUST NOT use the same keypair as any other log. 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 Maximum Chain Length: The longest chain submission the log is
willing 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 4.8).
Final STH: If a log has been closed down (i.e., no longer accepts Final STH: If a log has been closed down (i.e., no longer accepts
new entries), existing entries may still be valid. In this case, new entries), existing entries may still be valid. In this case,
the client should know the final valid STH in the log to ensure no the client should know the final valid STH in the log to ensure no
new entries can be added without detection. The final STH should new entries can be added without detection. The final STH should
be provided in the form of a TransItem of type be provided in the form of a TransItem of type
"signed_tree_head_v2". "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.
9.2. TLS Client 8.2. TLS Client
9.2.1. Receiving SCTs 8.2.1. Receiving SCTs
TLS clients receive SCTs alongside or in certificates. TLS clients TLS clients receive SCTs alongside or in certificates. TLS clients
MUST implement all of the three mechanisms by which TLS servers may MUST implement all of the three mechanisms by which TLS servers may
present SCTs (see Section 7). TLS clients MAY also accept SCTs via present SCTs (see Section 6). TLS clients MAY also accept SCTs via
the "status_request_v2" extension ([RFC6961]). TLS clients that the "status_request_v2" extension ([RFC6961]). TLS clients that
support the "transparency_info" TLS extension SHOULD include it in support the "transparency_info" TLS extension SHOULD include it in
ClientHello messages, with empty "extension_data". TLS clients may ClientHello messages, with empty "extension_data". TLS clients may
also receive inclusion proofs in addition to SCTs, which should be also receive inclusion proofs in addition to SCTs, which should be
checked once the SCTs are validated. checked once the SCTs are validated.
9.2.2. Reconstructing the TBSCertificate 8.2.2. 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 remove the Transparency Information a certificate, TLS clients should remove the Transparency Information
extension described in Section 8.1. extension described in Section 7.1.
If the SCT checked is for a Precertificate (where the "type" of the If the SCT checked is for a Precertificate (where the "type" of the
"TransItem" is "precert_sct_v2"), then the client SHOULD also remove "TransItem" is "precert_sct_v2"), then the client SHOULD also remove
embedded v1 SCTs, identified by OID 1.3.6.1.4.1.11129.2.4.2 (See embedded v1 SCTs, identified by OID 1.3.6.1.4.1.11129.2.4.2 (See
Section 3.3. of [RFC6962]), in the process of reconstructing the Section 3.3. of [RFC6962]), in the process of reconstructing the
TBSCertificate. That is to allow embedded v1 and v2 SCTs to co-exist TBSCertificate. That is to allow embedded v1 and v2 SCTs to co-exist
in a certificate (See Appendix A). in a certificate (See Appendix A).
9.2.3. Validating SCTs 8.2.3. Validating SCTs
In addition to normal validation of the server certificate and its In addition to normal validation of the server certificate and its
chain, TLS clients SHOULD validate each received SCT for which they chain, TLS clients SHOULD validate each received SCT for which they
have the corresponding log's metadata. To validate an SCT, a TLS have the corresponding log's metadata. To validate an SCT, a TLS
client computes the signature input from the SCT data and the client computes the signature input from the SCT data and the server
corresponding certificate, and then verifies the signature using the certificate, and then verifies the signature using the corresponding
corresponding log's public key. TLS clients MUST NOT consider valid log's public key. TLS clients MUST NOT consider valid any SCT whose
any SCT whose timestamp is in the future. timestamp is in the future.
Before considering any SCT to be invalid, the TLS client MUST attempt
to validate it against the server certificate and against each of the
zero or more suitable name-constrained intermediates (Section 4.2) in
the chain. These certificates may be evaluated in the order they
appear in the chain, or, indeed, in any order.
9.2.4. Validating inclusion proofs 8.2.4. 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 5.5) or "get-all-by-hash"
(Section 6.6), but note that this will disclose to the log which TLS (Section 5.6), but note that this will disclose to the log which TLS
server the client has been communicating with. server the client has been communicating with.
Alternatively, if the TLS client has received an inclusion proof (and Alternatively, if the TLS client has received an inclusion proof (and
an STH) alongside the SCT, it can proceed to verifying the inclusion an STH) alongside the SCT, it can proceed to verifying the inclusion
proof to the provided STH. The client then has to verify consistency proof to the provided STH. The client then has to verify consistency
between the provided STH and an STH it knows about, which is less between the provided STH and an STH it knows about, which is less
sensitive from a privacy perspective. sensitive from a privacy perspective.
TLS clients SHOULD also verify each received inclusion proof (see TLS clients SHOULD also verify each received inclusion proof (see
Section 9.4.1) for which they have the corresponding log's metadata, Section 8.4.1) 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 5.3),
then verify it by requesting a consistency proof (Section 6.4). Note then verify it by requesting a consistency proof (Section 5.4). Note
that if the TLS client uses "get-all-by-hash", then it will already that if the TLS client uses "get-all-by-hash", then it will already
have the new STH. have the new STH.
9.2.5. Evaluating compliance 8.2.5. 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.
A TLS client MUST NOT evaluate compliance if it did not send both the A TLS client MUST NOT evaluate compliance if it did not send both the
"transparency_info" and "status_request" TLS extensions in the "transparency_info" and "status_request" TLS extensions in the
ClientHello. ClientHello.
9.2.6. TLS Feature Extension 8.2.6. TLS Feature Extension
If any certificate in a chain includes the transparency_info If any certificate in a chain includes the transparency_info
(Section 7.5) TLS extension identifier in the TLS Feature [RFC7633] (Section 6.5) TLS extension identifier in the TLS Feature [RFC7633]
certificate extension, then CT compliance (using any of the certificate extension, then CT compliance (using any of the
mechanisms from Section 7) is required. mechanisms from Section 6) is required.
9.2.7. cached_info TLS Extension 8.2.7. cached_info TLS Extension
If a TLS client uses the "cached_info" TLS extension ([RFC7924]) to If a TLS client uses the "cached_info" TLS extension ([RFC7924]) to
indicate 1 or more cached certificates, all of which it already indicate 1 or more cached certificates, all of which it already
considers to be CT compliant, the TLS client MAY also include a considers to be CT compliant, the TLS client MAY also include a
"CachedObject" of type "ct_compliant" in the "cached_info" extension. "CachedObject" of type "ct_compliant" in the "cached_info" extension.
The "hash_value" field MUST be 1 byte long with the value 0. The "hash_value" field MUST be 1 byte long with the value 0.
9.2.8. Handling of Non-compliance 8.2.8. 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.
9.3. Monitor 8.3. Monitor
Monitors watch logs to check that they behave correctly, for Monitors watch logs to check that they behave correctly, for
certificates of interest, or both. For example, a monitor may be certificates of interest, or both. For example, a monitor may be
configured to report on all certificates that apply to a specific configured to report on all certificates that apply to a specific
domain name when fetching new entries for consistency validation. domain name when fetching new entries for consistency validation.
A monitor needs to, at least, inspect every new entry in each log it A monitor needs to, at least, inspect every new entry in each log it
watches. It may also want to keep copies of entire logs. In order watches. It may also want to keep copies of entire logs. In order
to do this, it should follow these steps for each log: to do this, it should follow these steps for each log:
1. Fetch the current STH (Section 6.3). 1. Fetch the current STH (Section 5.3).
2. Verify the STH signature. 2. Verify the STH signature.
3. Fetch all the entries in the tree corresponding to the STH 3. Fetch all the entries in the tree corresponding to the STH
(Section 6.7). (Section 5.7).
4. Confirm that the tree made from the fetched entries produces the 4. Confirm that the tree made from the fetched entries produces the
same hash as that in the STH. same hash as that in the STH.
5. Fetch the current STH (Section 6.3). Repeat until the STH 5. Fetch the current STH (Section 5.3). Repeat until the STH
changes. changes.
6. Verify the STH signature. 6. Verify the STH signature.
7. Fetch all the new entries in the tree corresponding to the STH 7. Fetch all the new entries in the tree corresponding to the STH
(Section 6.7). If they remain unavailable for an extended (Section 5.7). If they remain unavailable for an extended
period, then this should be viewed as misbehavior on the part of period, then this should be viewed as misbehavior on the part of
the log. the log.
8. Either: 8. Either:
1. Verify that the updated list of all entries generates a tree 1. Verify that the updated list of all entries generates a tree
with the same hash as the new STH. with the same hash as the new STH.
Or, if it is not keeping all log entries: Or, if it is not keeping all log entries:
1. Fetch a consistency proof for the new STH with the previous 1. Fetch a consistency proof for the new STH with the previous
STH (Section 6.4). STH (Section 5.4).
2. Verify the consistency proof. 2. Verify the consistency proof.
3. Verify that the new entries generate the corresponding 3. Verify that the new entries generate the corresponding
elements in the consistency proof. elements in the consistency proof.
9. Go to Step 5. 9. Go to Step 5.
9.4. Auditing 8.4. Auditing
Auditing ensures that the current published state of a log is Auditing ensures that the current published state of a log is
reachable from previously published states that are known to be good, reachable from previously published states that are known to be good,
and that the promises made by the log in the form of SCTs have been and that the promises made by the log in the form of SCTs have been
kept. Audits are performed by monitors or TLS clients. kept. Audits are performed by monitors or TLS clients.
In particular, there are four log behaviour properties that should be In particular, there are four log behaviour properties that should be
checked: checked:
o The Maximum Merge Delay (MMD). o The Maximum Merge Delay (MMD).
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derived from the previous STH and the submitted entries incorporated derived from the previous STH and the submitted entries incorporated
into the log since publication of the previous STH. This can be into the log since publication of the previous STH. This can be
proven through auditing of STHs. SCTs returned to TLS clients can be proven through auditing of STHs. SCTs returned to TLS clients can be
audited by verifying against the accompanying certificate, and using audited by verifying against the accompanying certificate, and using
Merkle Inclusion Proofs, against the log's Merkle tree. Merkle Inclusion Proofs, against the log's Merkle tree.
The action taken by the auditor if an audit fails is not specified, The action taken by the auditor if an audit fails is not specified,
but note that in general if audit fails, the auditor is in possession but note that in general if audit fails, the auditor is in possession
of signed proof of the log's misbehavior. of signed proof of the log's misbehavior.
A monitor (Section 9.3) can audit by verifying the consistency of A monitor (Section 8.3) can audit by verifying the consistency of
STHs it receives, ensure that each entry can be fetched and that the STHs it receives, ensure that each entry can be fetched and that the
STH is indeed the result of making a tree from all fetched entries. STH is indeed the result of making a tree from all fetched entries.
A TLS client (Section 9.2) can audit by verifying an SCT against any A TLS client (Section 8.2) 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 5.5). It can also
verify that the SCT corresponds to the certificate it arrived with verify that the SCT corresponds to the server certificate it arrived
(i.e., the log entry is that certificate, is a precertificate for with (i.e., the log entry is that certificate, or is a precertificate
that certificate or is an appropriate name-constrained intermediate corresponding to that certificate).
(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 12.3. Section 11.3.
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.
9.4.1. Verifying an inclusion proof 8.4.1. Verifying an inclusion proof
When a client has received a "TransItem" of type "inclusion_proof_v2" When a client has received a "TransItem" of type "inclusion_proof_v2"
and wishes to verify inclusion of an input "hash" for an STH with a and wishes to verify inclusion of an input "hash" for an STH with a
given "tree_size" and "root_hash", the following algorithm may be given "tree_size" and "root_hash", the following algorithm may be
used to prove the "hash" was included in the "root_hash": used to prove the "hash" was included in the "root_hash":
1. Compare "leaf_index" against "tree_size". If "leaf_index" is 1. Compare "leaf_index" against "tree_size". If "leaf_index" is
greater than or equal to "tree_size" fail the proof verification. greater than or equal to "tree_size" fail the proof verification.
2. Set "fn" to "leaf_index" and "sn" to "tree_size - 1". 2. Set "fn" to "leaf_index" and "sn" to "tree_size - 1".
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1. 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.
9.4.2. Verifying consistency between two STHs 8.4.2. Verifying consistency between two STHs
When a client has an STH "first_hash" for tree size "first", an STH When a client has an STH "first_hash" for tree size "first", an STH
"second_hash" for tree size "second" where "0 < first < second", and "second_hash" for tree size "second" where "0 < first < second", and
has received a "TransItem" of type "consistency_proof_v2" that they has received a "TransItem" of type "consistency_proof_v2" that they
wish to use to verify both hashes, the following algorithm may be wish to use to verify both hashes, the following algorithm may be
used: used:
1. If "first" is an exact power of 2, then prepend "first_hash" to 1. If "first" is an exact power of 2, then prepend "first_hash" to
the "consistency_path" array. the "consistency_path" array.
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1. 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.
9.4.3. Verifying root hash given entries 8.4.3. Verifying root hash given entries
When a client has a complete list of leaf input "entries" from "0" up When a client has a complete list of leaf input "entries" from "0" up
to "tree_size - 1" and wishes to verify this list against an STH to "tree_size - 1" and wishes to verify this list against an STH
"root_hash" returned by the log for the same "tree_size", the "root_hash" returned by the log for the same "tree_size", the
following algorithm may be used: following algorithm may be used:
1. Set "stack" to an empty stack. 1. Set "stack" to an empty stack.
2. For each "i" from "0" up to "tree_size - 1": 2. For each "i" from "0" up to "tree_size - 1":
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3. Push "HASH(0x01 || left || right)" to "stack". 3. Push "HASH(0x01 || left || right)" to "stack".
3. If there is more than one element in the "stack", repeat the same 3. If there is more than one element in the "stack", repeat the same
merge procedure (Step 2.3 above) until only a single element merge procedure (Step 2.3 above) until only a single element
remains. remains.
4. The remaining element in "stack" is the Merkle Tree hash for the 4. The remaining element in "stack" is the Merkle Tree hash for the
given "tree_size" and should be compared by equality against the given "tree_size" and should be compared by equality against the
supplied "root_hash". supplied "root_hash".
10. Algorithm Agility 9. Algorithm Agility
It is not possible for a log to change any of its algorithms part way It is not possible for a log to change any of its algorithms part way
through its lifetime: through its lifetime:
Signature algorithm: SCT signatures must remain valid so signature Signature algorithm: SCT signatures must remain valid so signature
algorithms can only be added, not removed. algorithms can only be added, not removed.
Hash algorithm: A log would have to support the old and new hash Hash algorithm: A log would have to support the old and new hash
algorithms to allow backwards-compatibility with clients that are algorithms to allow backwards-compatibility with clients that are
not aware of a hash algorithm change. not aware of a hash algorithm change.
Allowing multiple signature or hash algorithms for a log would Allowing multiple signature or hash algorithms for a log would
require that all data structures support it and would significantly require that all data structures support it and would significantly
complicate client implementation, which is why it is not supported by complicate client implementation, which is why it is not supported by
this document. this document.
If it should become necessary to deprecate an algorithm used by a If it should become necessary to deprecate an algorithm used by a
live log, then the log should be frozen as specified in Section 9.1 live log, then the log should be frozen as specified in Section 8.1
and a new log should be started. Certificates in the frozen log that and a new log should be started. Certificates in the frozen log that
have not yet expired and require new SCTs SHOULD be submitted to the have not yet expired and require new SCTs SHOULD be submitted to the
new log and the SCTs from that log used instead. new log and the SCTs from that log used instead.
11. IANA Considerations 10. IANA Considerations
The assignment policy criteria mentioned in this section refer to the The assignment policy criteria mentioned in this section refer to the
policies outlined in [RFC5226]. policies outlined in [RFC5226].
11.1. TLS Extension Type 10.1. TLS Extension Type
IANA is asked to allocate an RFC 5246 ExtensionType value for the IANA is asked to allocate an RFC 5246 ExtensionType value for the
"transparency_info" TLS extension. IANA should update this extension "transparency_info" TLS extension. IANA should update this extension
type to point at this document. type to point at this document.
11.2. New Entry to the TLS CachedInformationType registry 10.2. New Entry to the TLS CachedInformationType registry
IANA is asked to add an entry for "ct_compliant(TBD)" to the "TLS IANA is asked to add an entry for "ct_compliant(TBD)" to the "TLS
CachedInformationType Values" registry that was defined in [RFC7924]. CachedInformationType Values" registry that was defined in [RFC7924].
11.3. Hash Algorithms 10.3. Hash Algorithms
IANA is asked to establish a registry of hash algorithm values, named IANA is asked to establish a registry of hash algorithm values, named
"CT Hash Algorithms", that initially consists of: "CT Hash Algorithms", that initially consists of:
+------------+---------------+--------------------------------------+ +------------+---------------+--------------------------------------+
| Value | Hash | Reference / Assignment Policy | | Value | Hash | Reference / Assignment Policy |
| | Algorithm | | | | Algorithm | |
+------------+---------------+--------------------------------------+ +------------+---------------+--------------------------------------+
| 0x00 | SHA-256 | [RFC4634] | | 0x00 | SHA-256 | [RFC4634] |
| | | | | | | |
| 0x01 - | Unassigned | Specification Required and Expert | | 0x01 - | Unassigned | Specification Required and Expert |
| 0xDF | | Review | | 0xDF | | Review |
| | | | | | | |
| 0xE0 - | Reserved | Experimental Use | | 0xE0 - | Reserved | Experimental Use |
| 0xEF | | | | 0xEF | | |
| | | | | | | |
| 0xF0 - | Reserved | Private Use | | 0xF0 - | Reserved | Private Use |
| 0xFF | | | | 0xFF | | |
+------------+---------------+--------------------------------------+ +------------+---------------+--------------------------------------+
11.3.1. Expert Review guidelines 10.3.1. Expert Review guidelines
The appointed Expert should ensure that the proposed algorithm has a The appointed Expert should ensure that the proposed algorithm has a
public specification and is suitable for use as a cryptographic hash public specification and is suitable for use as a cryptographic hash
algorithm with no known preimage or collision attacks. These attacks algorithm with no known preimage or collision attacks. These attacks
can damage the integrity of the log. can damage the integrity of the log.
11.4. Signature Algorithms 10.4. Signature Algorithms
IANA is asked to establish a registry of signature algorithm values, IANA is asked to establish a registry of signature algorithm values,
named "CT Signature Algorithms", that initially consists of: named "CT Signature Algorithms", that initially consists of:
+---------+-------------------------------+-------------------------+ +---------+-------------------------------+-------------------------+
| Value | Signature Algorithm | Reference / Assignment | | Value | Signature Algorithm | Reference / Assignment |
| | | Policy | | | | Policy |
+---------+-------------------------------+-------------------------+ +---------+-------------------------------+-------------------------+
| 0x00 | Deterministic ECDSA (NIST | [RFC6979] | | 0x00 | Deterministic ECDSA (NIST | [RFC6979] |
| | P-256) with HMAC-SHA256 | | | | P-256) with HMAC-SHA256 | |
skipping to change at page 45, line 30 skipping to change at page 44, line 25
| 0x02 - | Unassigned | Specification Required | | 0x02 - | Unassigned | Specification Required |
| 0xDF | | and Expert Review | | 0xDF | | and Expert Review |
| | | | | | | |
| 0xE0 - | Reserved | Experimental Use | | 0xE0 - | Reserved | Experimental Use |
| 0xEF | | | | 0xEF | | |
| | | | | | | |
| 0xF0 - | Reserved | Private Use | | 0xF0 - | Reserved | Private Use |
| 0xFF | | | | 0xFF | | |
+---------+-------------------------------+-------------------------+ +---------+-------------------------------+-------------------------+
11.4.1. Expert Review guidelines 10.4.1. Expert Review guidelines
The appointed Expert should ensure that the proposed algorithm has a The appointed Expert should ensure that the proposed algorithm has a
public specification and is suitable for use as a cryptographic public specification and is suitable for use as a cryptographic
signature algorithm that always generates signatures signature algorithm that always generates signatures
deterministically (for the reasons listed in Section 12.4). deterministically (for the reasons listed in Section 11.4).
11.5. VersionedTransTypes 10.5. VersionedTransTypes
IANA is asked to establish a registry of "VersionedTransType" values, IANA is asked to establish a registry of "VersionedTransType" values,
named "CT VersionedTransTypes", that initially consists of: named "CT VersionedTransTypes", that initially consists of:
+------------+---------------------------+--------------------------+ +------------+---------------------------+--------------------------+
| Value | Type and Version | Reference / Assignment | | Value | Type and Version | Reference / Assignment |
| | | Policy | | | | Policy |
+------------+---------------------------+--------------------------+ +------------+---------------------------+--------------------------+
| 0x0000 | Reserved | [RFC6962] (*) | | 0x0000 | Reserved | [RFC6962] (*) |
| | | | | | | |
skipping to change at page 46, line 45 skipping to change at page 45, line 45
| 0xF000 - | Reserved | Private Use | | 0xF000 - | Reserved | Private Use |
| 0xFFFF | | | | 0xFFFF | | |
+------------+---------------------------+--------------------------+ +------------+---------------------------+--------------------------+
(*) The 0x0000 value is reserved so that v1 SCTs are distinguishable (*) The 0x0000 value is reserved so that v1 SCTs are distinguishable
from v2 SCTs and other "TransItem" structures. from v2 SCTs and other "TransItem" structures.
[RFC Editor: please update 'RFCXXXX' to refer to this document, once [RFC Editor: please update 'RFCXXXX' to refer to this document, once
its RFC number is known.] its RFC number is known.]
11.5.1. Expert Review guidelines 10.5.1. Expert Review guidelines
The appointed Expert should review the public specification to ensure The appointed Expert should review the public specification to ensure
that it is detailed enough to ensure implementation interoperability. that it is detailed enough to ensure implementation interoperability.
11.6. SCT Extensions 10.6. SCT Extensions
IANA is asked to establish a registry of SCT extensions, named "CT IANA is asked to establish a registry of SCT extensions, named "CT
Extension Types for SCT", that initially consists of: Extension Types for SCT", that initially consists of:
+----------------+------------+-------------------------------------+ +----------------+------------+-------------------------------------+
| Value | Extension | Reference / Assignment Policy | | Value | Extension | Reference / Assignment Policy |
+----------------+------------+-------------------------------------+ +----------------+------------+-------------------------------------+
| 0x0000 - | Unassigned | Specification Required and Expert | | 0x0000 - | Unassigned | Specification Required and Expert |
| 0xDFFF | | Review | | 0xDFFF | | Review |
| | | | | | | |
| 0xE000 - | Reserved | Experimental Use | | 0xE000 - | Reserved | Experimental Use |
| 0xEFFF | | | | 0xEFFF | | |
| | | | | | | |
| 0xF000 - | Reserved | Private Use | | 0xF000 - | Reserved | Private Use |
| 0xFFFF | | | | 0xFFFF | | |
+----------------+------------+-------------------------------------+ +----------------+------------+-------------------------------------+
11.6.1. Expert Review guidelines 10.6.1. Expert Review guidelines
The appointed Expert should review the public specification to ensure The appointed Expert should review the public specification to ensure
that it is detailed enough to ensure implementation interoperability. that it is detailed enough to ensure implementation interoperability.
11.7. STH Extensions 10.7. STH Extensions
IANA is asked to establish a registry of STH extensions, named "CT IANA is asked to establish a registry of STH extensions, named "CT
Extension Types for STH", that initially consists of: Extension Types for STH", that initially consists of:
+----------------+------------+-------------------------------------+ +----------------+------------+-------------------------------------+
| Value | Extension | Reference / Assignment Policy | | Value | Extension | Reference / Assignment Policy |
+----------------+------------+-------------------------------------+ +----------------+------------+-------------------------------------+
| 0x0000 - | Unassigned | Specification Required and Expert | | 0x0000 - | Unassigned | Specification Required and Expert |
| 0xDFFF | | Review | | 0xDFFF | | Review |
| | | | | | | |
| 0xE000 - | Reserved | Experimental Use | | 0xE000 - | Reserved | Experimental Use |
| 0xEFFF | | | | 0xEFFF | | |
| | | | | | | |
| 0xF000 - | Reserved | Private Use | | 0xF000 - | Reserved | Private Use |
| 0xFFFF | | | | 0xFFFF | | |
+----------------+------------+-------------------------------------+ +----------------+------------+-------------------------------------+
11.7.1. Expert Review guidelines 10.7.1. Expert Review guidelines
The appointed Expert should review the public specification to ensure The appointed Expert should review the public specification to ensure
that it is detailed enough to ensure implementation interoperability. that it is detailed enough to ensure implementation interoperability.
11.8. Object Identifiers 10.8. 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 4.3), the precertificate CMS "eContentType" (see
Section 3.2), and X.509v3 extensions in certificates (see Section 4.2 Section 3.2), and X.509v3 extensions in certificates (see
and Section 8.1.2) and OCSP responses (see Section 8.1.1). The OIDs Section 7.1.2) and OCSP responses (see Section 7.1.1). The OIDs are
are defined in an arc that was selected due to its short encoding. defined in an arc that was selected due to its short encoding.
11.8.1. Log ID Registry 10.8.1. Log ID Registry
IANA is asked to establish a registry of Log IDs, named "CT Log ID IANA is asked to establish a registry of Log IDs, named "CT Log ID
Registry", that initially consists of: Registry", that initially consists of:
+-------------------------+------------+----------------------------+ +-------------------------+------------+----------------------------+
| Value | Log | Reference / Assignment | | Value | Log | Reference / Assignment |
| | | Policy | | | | Policy |
+-------------------------+------------+----------------------------+ +-------------------------+------------+----------------------------+
| 1.3.101.8192 - | Unassigned | Metadata Required and | | 1.3.101.8192 - | Unassigned | Metadata Required and |
| 1.3.101.16383 | | Expert Review | | 1.3.101.16383 | | Expert Review |
skipping to change at page 48, line 42 skipping to change at page 47, line 42
All OIDs in the range from 1.3.101.8192 to 1.3.101.16383 have been All OIDs in the range from 1.3.101.8192 to 1.3.101.16383 have been
reserved. This is a limited resource of 8,192 OIDs, each of which reserved. This is a limited resource of 8,192 OIDs, each of which
has an encoded length of 4 octets. has an encoded length of 4 octets.
The 1.3.101.80 arc has been delegated. This is an unlimited The 1.3.101.80 arc has been delegated. This is an unlimited
resource, but only the 128 OIDs from 1.3.101.80.0 to 1.3.101.80.127 resource, but only the 128 OIDs from 1.3.101.80.0 to 1.3.101.80.127
have an encoded length of only 4 octets. have an encoded length of only 4 octets.
Each application for the allocation of a Log ID should be accompanied Each application for the allocation of a Log ID should be accompanied
by all of the required metadata (except for the Log ID) listed in by all of the required metadata (except for the Log ID) listed in
Section 9.1. Section 8.1.
11.8.2. Expert Review guidelines 10.8.2. Expert Review guidelines
Since the Log IDs with the shortest encodings are a limited resource, Since the Log IDs with the shortest encodings are a limited resource,
the appointed Expert should review the submitted metadata and judge the appointed Expert should review the submitted metadata and judge
whether or not the applicant is requesting a Log ID in good faith whether or not the applicant is requesting a Log ID in good faith
(with the intention of actually running a CT log that will be (with the intention of actually running a CT log that will be
identified by the allocated Log ID). identified by the allocated Log ID).
12. Security Considerations 11. Security Considerations
With CAs, logs, and servers performing the actions described here, With CAs, logs, and servers performing the actions described here,
TLS clients can use logs and signed timestamps to reduce the TLS clients can use logs and signed timestamps to reduce the
likelihood that they will accept misissued certificates. If a server likelihood that they will accept misissued certificates. If a server
presents a valid signed timestamp for a certificate, then the client presents a valid signed timestamp for a certificate, then the client
knows that a log has committed to publishing the certificate. From knows that a log has committed to publishing the certificate. From
this, the client knows that monitors acting for the subject of the this, the client knows that monitors acting for the subject of the
certificate have had some time to notice the misissue and take some certificate have had some time to notice the misissue and take some
action, such as asking a CA to revoke a misissued certificate, or action, such as asking a CA to revoke a misissued certificate, or
that the log has misbehaved, which will be discovered when the SCT is that the log has misbehaved, which will be discovered when the SCT is
skipping to change at page 49, line 28 skipping to change at page 48, line 28
the logs or the CA might have refused to revoke the certificate. the logs or the CA might have refused to revoke the certificate.
In addition, if TLS clients will not accept unlogged certificates, In addition, if TLS clients will not accept unlogged certificates,
then site owners will have a greater incentive to submit certificates then site owners will have a greater incentive to submit certificates
to logs, possibly with the assistance of their CA, increasing the to logs, possibly with the assistance of their CA, increasing the
overall transparency of the system. overall transparency of the system.
[I-D.ietf-trans-threat-analysis] provides a more detailed threat [I-D.ietf-trans-threat-analysis] provides a more detailed threat
analysis of the Certificate Transparency architecture. analysis of the Certificate Transparency architecture.
12.1. Misissued Certificates 11.1. Misissued Certificates
Misissued certificates that have not been publicly logged, and thus Misissued certificates that have not been publicly logged, and thus
do not have a valid SCT, are not considered compliant. Misissued do not have a valid SCT, are not considered compliant. Misissued
certificates that do have an SCT from a log will appear in that certificates that do have an SCT from a log will appear in that
public log within the Maximum Merge Delay, assuming the log is public log within the Maximum Merge Delay, assuming the log is
operating correctly. Thus, the maximum period of time during which a operating correctly. 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.
12.2. Detection of Misissue 11.2. Detection of Misissue
The logs do not themselves detect misissued certificates; they rely The logs do not themselves detect misissued certificates; they rely
instead on interested parties, such as domain owners, to monitor them instead on interested parties, such as domain owners, to monitor them
and take corrective action when a misissue is detected. and take corrective action when a misissue is detected.
12.3. Misbehaving Logs 11.3. Misbehaving Logs
A log can misbehave in several ways. Examples include failing to A log can misbehave in several ways. Examples include failing to
incorporate a certificate with an SCT in the Merkle Tree within the incorporate a certificate with an SCT in the Merkle Tree within the
MMD, presenting different, conflicting views of the Merkle Tree at MMD, presenting different, conflicting views of the Merkle Tree at
different times and/or to different parties and issuing STHs too different times and/or to different parties and issuing STHs too
frequently. Such misbehavior is detectable and the frequently. Such misbehavior is detectable and 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
Merkle inclusion proof (Section 6.5) for each observed SCT. These Merkle inclusion proof (Section 5.5) for each observed SCT. These
checks can be asynchronous and need only be done once per each checks can be asynchronous and need only be done once per each
certificate. In order to protect the clients' privacy, these checks certificate. In order to protect the clients' privacy, these checks
need not reveal the exact certificate to the log. Instead, clients need not reveal the exact certificate to the log. Instead, clients
can request the proof from a trusted auditor (since anyone can can request the proof from a trusted auditor (since anyone can
compute the proofs from the log) or communicate with the log via compute the proofs from the log) or communicate with the log via
proxies. proxies.
Violation of the append-only property or the STH issuance rate limit Violation of the append-only property or the STH issuance rate limit
can be detected by clients comparing their instances of the Signed can be detected by clients comparing their instances of the Signed
Tree Heads. There are various ways this could be done, for example Tree Heads. There are various ways this could be done, for example
via gossip (see [I-D.ietf-trans-gossip]) or peer-to-peer via gossip (see [I-D.ietf-trans-gossip]) or peer-to-peer
communications or by sending STHs to monitors (who could then communications or by sending STHs to monitors (who could then
directly check against their own copy of the relevant log). A proof directly check against their own copy of the relevant log). A proof
of misbehavior in such cases would be a series of STHs that were of misbehavior in such cases would be a series of STHs that were
issued too closely together, proving violation of the STH issuance issued too closely together, proving violation of the STH issuance
rate limit, or an STH with a root hash that does not match the one rate limit, or an STH with a root hash that does not match the one
calculated from a copy of the log, proving violation of the append- calculated from a copy of the log, proving violation of the append-
only property. only property.
12.4. Deterministic Signatures 11.4. 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.
12.5. Multiple SCTs 11.5. Multiple SCTs
By offering multiple SCTs, each from a different log, TLS servers By offering multiple SCTs, each from a different log, TLS servers
reduce the effectiveness of an attack where a CA and a log collude reduce the effectiveness of an attack where a CA and a log collude
(see Section 7.1). (see Section 6.1).
13. Acknowledgements 12. Acknowledgements
The authors would like to thank Erwann Abelea, Robin Alden, Andrew The authors would like to thank Erwann Abelea, Robin Alden, Andrew
Ayer, Al Cutter, David Drysdale, Francis Dupont, Adam Eijdenberg, Ayer, Al Cutter, David Drysdale, Francis Dupont, Adam Eijdenberg,
Stephen Farrell, Daniel Kahn Gillmor, Paul Hadfield, Brad Hill, Jeff Stephen Farrell, Daniel Kahn Gillmor, Paul Hadfield, Brad Hill, Jeff
Hodges, Paul Hoffman, Jeffrey Hutzelman, Kat Joyce, Stephen Kent, SM, Hodges, Paul Hoffman, Jeffrey Hutzelman, Kat Joyce, Stephen Kent, SM,
Alexey 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.
14. References 13. References
14.1. Normative References 13.1. Normative References
[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, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>. <http://www.rfc-editor.org/info/rfc2119>.
skipping to change at page 52, line 5 skipping to change at page 51, line 5
[RFC5905] Mills, D., Martin, J., Ed., Burbank, J., and W. Kasch, [RFC5905] Mills, D., Martin, J., Ed., Burbank, J., and W. Kasch,
"Network Time Protocol Version 4: Protocol and Algorithms "Network Time Protocol Version 4: Protocol and Algorithms
Specification", RFC 5905, DOI 10.17487/RFC5905, June 2010, Specification", RFC 5905, DOI 10.17487/RFC5905, June 2010,
<http://www.rfc-editor.org/info/rfc5905>. <http://www.rfc-editor.org/info/rfc5905>.
[RFC6066] Eastlake 3rd, D., "Transport Layer Security (TLS) [RFC6066] Eastlake 3rd, D., "Transport Layer Security (TLS)
Extensions: Extension Definitions", RFC 6066, Extensions: Extension Definitions", RFC 6066,
DOI 10.17487/RFC6066, January 2011, DOI 10.17487/RFC6066, January 2011,
<http://www.rfc-editor.org/info/rfc6066>. <http://www.rfc-editor.org/info/rfc6066>.
[RFC6125] Saint-Andre, P. and J. Hodges, "Representation and
Verification of Domain-Based Application Service Identity
within Internet Public Key Infrastructure Using X.509
(PKIX) Certificates in the Context of Transport Layer
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,
<http://www.rfc-editor.org/info/rfc6961>. <http://www.rfc-editor.org/info/rfc6961>.
skipping to change at page 52, line 46 skipping to change at page 51, line 39
[RFC7924] Santesson, S. and H. Tschofenig, "Transport Layer Security [RFC7924] Santesson, S. and H. Tschofenig, "Transport Layer Security
(TLS) Cached Information Extension", RFC 7924, (TLS) Cached Information Extension", RFC 7924,
DOI 10.17487/RFC7924, July 2016, DOI 10.17487/RFC7924, July 2016,
<http://www.rfc-editor.org/info/rfc7924>. <http://www.rfc-editor.org/info/rfc7924>.
[RFC8017] Moriarty, K., Ed., Kaliski, B., Jonsson, J., and A. Rusch, [RFC8017] Moriarty, K., Ed., Kaliski, B., Jonsson, J., and A. Rusch,
"PKCS #1: RSA Cryptography Specifications Version 2.2", "PKCS #1: RSA Cryptography Specifications Version 2.2",
RFC 8017, DOI 10.17487/RFC8017, November 2016, RFC 8017, DOI 10.17487/RFC8017, November 2016,
<http://www.rfc-editor.org/info/rfc8017>. <http://www.rfc-editor.org/info/rfc8017>.
14.2. Informative References 13.2. Informative References
[Chromium.Log.Policy] [Chromium.Log.Policy]
The Chromium Projects, "Chromium Certificate Transparency The Chromium Projects, "Chromium Certificate Transparency
Log Policy", 2014, <http://www.chromium.org/Home/chromium- Log Policy", 2014, <http://www.chromium.org/Home/chromium-
security/certificate-transparency/log-policy>. security/certificate-transparency/log-policy>.
[Chromium.Policy] [Chromium.Policy]
The Chromium Projects, "Chromium Certificate The Chromium Projects, "Chromium Certificate
Transparency", 2014, <http://www.chromium.org/Home/ Transparency", 2014, <http://www.chromium.org/Home/
chromium-security/certificate-transparency>. chromium-security/certificate-transparency>.
[CrosbyWallach] [CrosbyWallach]
Crosby, S. and D. Wallach, "Efficient Data Structures for Crosby, S. and D. Wallach, "Efficient Data Structures for
Tamper-Evident Logging", Proceedings of the 18th USENIX Tamper-Evident Logging", Proceedings of the 18th USENIX
Security Symposium, Montreal, August 2009, Security Symposium, Montreal, August 2009,
<http://static.usenix.org/event/sec09/tech/full_papers/ <http://static.usenix.org/event/sec09/tech/full_papers/
crosby.pdf>. crosby.pdf>.
[EVSSLGuidelines]
CA/Browser Forum, "Guidelines For The Issuance And
Management Of Extended Validation Certificates", 2007,
<https://cabforum.org/wp-content/uploads/
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-03 (work in progress), July CT", draft-ietf-trans-gossip-03 (work in progress), July
2016. 2016.
[I-D.ietf-trans-threat-analysis] [I-D.ietf-trans-threat-analysis]
Kent, S., "Attack and Threat Model for Certificate Kent, S., "Attack and Threat Model for Certificate
Transparency", draft-ietf-trans-threat-analysis-10 (work Transparency", draft-ietf-trans-threat-analysis-10 (work
in progress), October 2016. in progress), October 2016.
skipping to change at page 54, line 33 skipping to change at page 53, line 21
before submission of the TBSCertificate (inside a v1 precertificate, before submission of the TBSCertificate (inside a v1 precertificate,
as described in Section 3.1. of [RFC6962]) to a v1 log so that TLS as described in Section 3.1. of [RFC6962]) to a v1 log so that TLS
clients conforming to [RFC6962] but not this document are oblivious clients conforming to [RFC6962] but not this document are oblivious
to the embedded v2 SCTs. An issuer can follow these steps to produce to the embedded v2 SCTs. An issuer can follow these steps to produce
an X.509 certificate with embedded v1 and v2 SCTs: an X.509 certificate with embedded v1 and v2 SCTs:
o Create a CMS precertificate as described in Section 3.2 and submit o Create a CMS precertificate as described in Section 3.2 and submit
it to v2 logs. it to v2 logs.
o Embed the obtained v2 SCTs in the TBSCertificate, as described in o Embed the obtained v2 SCTs in the TBSCertificate, as described in
Section 8.1.2. Section 7.1.2.
o Use that TBSCertificate to create a v1 precertificate, as o Use that TBSCertificate to create a v1 precertificate, as
described in Section 3.1. of [RFC6962] and submit it to v1 logs. described in Section 3.1. of [RFC6962] and submit it to v1 logs.
o Embed the v1 SCTs in the TBSCertificate, as described in o Embed the v1 SCTs in the TBSCertificate, as described in
Section 3.3. of [RFC6962]. Section 3.3. of [RFC6962].
o Sign that TBSCertificate (which now contains v1 and v2 SCTs) to o Sign that TBSCertificate (which now contains v1 and v2 SCTs) to
issue the final X.509 certificate. issue the final X.509 certificate.
 End of changes. 157 change blocks. 
354 lines changed or deleted 256 lines changed or added

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