draft-ietf-trans-rfc6962-bis-05.txt   draft-ietf-trans-rfc6962-bis-06.txt 
Public Notary Transparency Working Group B. Laurie Public Notary Transparency Working Group B. Laurie
Internet-Draft A. Langley Internet-Draft A. Langley
Intended status: Standards Track E. Kasper Intended status: Standards Track E. Kasper
Expires: July 31, 2015 E. Messeri Expires: September 10, 2015 E. Messeri
Google Google
R. Stradling R. Stradling
Comodo Comodo
January 27, 2015 March 9, 2015
Certificate Transparency Certificate Transparency
draft-ietf-trans-rfc6962-bis-05 draft-ietf-trans-rfc6962-bis-06
Abstract Abstract
This document describes a protocol for publicly logging the existence This document describes a protocol for publicly logging the existence
of Transport Layer Security (TLS) certificates as they are issued or of Transport Layer Security (TLS) certificates as they are issued or
observed, in a manner that allows anyone to audit certificate observed, in a manner that allows anyone to audit certification
authority (CA) activity and notice the issuance of suspect authority (CA) activity and notice the issuance of suspect
certificates as well as to audit the certificate logs themselves. certificates as well as to audit the certificate logs themselves.
The intent is that eventually clients would refuse to honor The intent is that eventually clients would refuse to honor
certificates that do not appear in a log, effectively forcing CAs to certificates that do not appear in a log, effectively forcing CAs to
add all issued certificates to the logs. add all issued certificates to the logs.
Logs are network services that implement the protocol operations for Logs are network services that implement the protocol operations for
submissions and queries that are defined in this document. submissions and queries that are defined in this document.
Status of This Memo Status of This Memo
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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-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on July 31, 2015. This Internet-Draft will expire on September 10, 2015.
Copyright Notice Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the Copyright (c) 2015 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
carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Informal Introduction . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 4 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 4
1.2. Data Structures . . . . . . . . . . . . . . . . . . . . . 4 1.2. Data Structures . . . . . . . . . . . . . . . . . . . . . 4
2. Cryptographic Components . . . . . . . . . . . . . . . . . . 4 2. Cryptographic Components . . . . . . . . . . . . . . . . . . 4
2.1. Merkle Hash Trees . . . . . . . . . . . . . . . . . . . . 4 2.1. Merkle Hash Trees . . . . . . . . . . . . . . . . . . . . 5
2.1.1. Merkle Inclusion Proofs . . . . . . . . . . . . . . . 5 2.1.1. Merkle Inclusion Proofs . . . . . . . . . . . . . . . 5
2.1.2. Merkle Consistency Proofs . . . . . . . . . . . . . . 6 2.1.2. Merkle Consistency Proofs . . . . . . . . . . . . . . 6
2.1.3. Example . . . . . . . . . . . . . . . . . . . . . . . 7 2.1.3. Example . . . . . . . . . . . . . . . . . . . . . . . 7
2.1.4. Signatures . . . . . . . . . . . . . . . . . . . . . 8 2.1.4. Signatures . . . . . . . . . . . . . . . . . . . . . 9
3. Log Format and Operation . . . . . . . . . . . . . . . . . . 9 3. Log Format and Operation . . . . . . . . . . . . . . . . . . 9
3.1. Log Entries . . . . . . . . . . . . . . . . . . . . . . . 9 3.1. Log Entries . . . . . . . . . . . . . . . . . . . . . . . 9
3.2. Private Domain Name Labels . . . . . . . . . . . . . . . 12 3.2. Private Domain Name Labels . . . . . . . . . . . . . . . 12
3.2.1. Wildcard Certificates . . . . . . . . . . . . . . . . 12 3.2.1. Wildcard Certificates . . . . . . . . . . . . . . . . 12
3.2.2. Redacting Domain Name Labels in Precertificates . . . 12 3.2.2. Redacting Domain Name Labels in Precertificates . . . 12
3.2.3. Using a Name-Constrained Intermediate CA . . . . . . 13 3.2.3. Using a Name-Constrained Intermediate CA . . . . . . 13
3.3. Structure of the Signed Certificate Timestamp . . . . . . 14 3.3. Structure of the Signed Certificate Timestamp . . . . . . 14
3.4. Including the Signed Certificate Timestamp in the TLS 3.4. Including the Signed Certificate Timestamp in the TLS
Handshake . . . . . . . . . . . . . . . . . . . . . . . . 15 Handshake . . . . . . . . . . . . . . . . . . . . . . . . 15
3.4.1. TLS Extension . . . . . . . . . . . . . . . . . . . . 16 3.4.1. TLS Extension . . . . . . . . . . . . . . . . . . . . 17
3.5. Merkle Tree . . . . . . . . . . . . . . . . . . . . . . . 16 3.5. Merkle Tree . . . . . . . . . . . . . . . . . . . . . . . 17
3.6. Signed Tree Head . . . . . . . . . . . . . . . . . . . . 17 3.6. Signed Tree Head . . . . . . . . . . . . . . . . . . . . 18
4. Log Client Messages . . . . . . . . . . . . . . . . . . . . . 18 4. Log Client Messages . . . . . . . . . . . . . . . . . . . . . 19
4.1. Add Chain to Log . . . . . . . . . . . . . . . . . . . . 19 4.1. Add Chain to Log . . . . . . . . . . . . . . . . . . . . 21
4.2. Add PreCertChain to Log . . . . . . . . . . . . . . . . . 20 4.2. Add PreCertChain to Log . . . . . . . . . . . . . . . . . 22
4.3. Retrieve Latest Signed Tree Head . . . . . . . . . . . . 21 4.3. Retrieve Latest Signed Tree Head . . . . . . . . . . . . 22
4.4. Retrieve Merkle Consistency Proof between Two Signed Tree 4.4. Retrieve Merkle Consistency Proof between Two Signed Tree
Heads . . . . . . . . . . . . . . . . . . . . . . . . . . 21 Heads . . . . . . . . . . . . . . . . . . . . . . . . . . 23
4.5. Retrieve Merkle Inclusion Proof from Log by Leaf Hash . . 21 4.5. Retrieve Merkle Inclusion Proof from Log by Leaf Hash . . 23
4.6. Retrieve Entries from Log . . . . . . . . . . . . . . . . 22 4.6. Retrieve Merkle Inclusion Proof, Signed Tree Head and
4.7. Retrieve Accepted Root Certificates . . . . . . . . . . . 23 Consistency Proof by Leaf Hash . . . . . . . . . . . . . 24
4.8. Retrieve Entry+Merkle Inclusion Proof from Log . . . . . 23 4.7. Retrieve Entries from Log . . . . . . . . . . . . . . . . 25
4.8. Retrieve Accepted Root Certificates . . . . . . . . . . . 26
5. Clients . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 5. Clients . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
5.1. Submitters . . . . . . . . . . . . . . . . . . . . . . . 24 5.1. Metadata . . . . . . . . . . . . . . . . . . . . . . . . 27
5.2. TLS Client . . . . . . . . . . . . . . . . . . . . . . . 24 5.2. Submitters . . . . . . . . . . . . . . . . . . . . . . . 28
5.3. Monitor . . . . . . . . . . . . . . . . . . . . . . . . . 25 5.3. TLS Client . . . . . . . . . . . . . . . . . . . . . . . 28
5.4. Auditor . . . . . . . . . . . . . . . . . . . . . . . . . 26 5.4. Monitor . . . . . . . . . . . . . . . . . . . . . . . . . 28
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 26 5.5. Auditing . . . . . . . . . . . . . . . . . . . . . . . . 29
6.1. TLS Extension Type . . . . . . . . . . . . . . . . . . . 26 6. Algorithm Agility . . . . . . . . . . . . . . . . . . . . . . 30
6.2. Hash Algorithms . . . . . . . . . . . . . . . . . . . . . 26 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 30
7. Security Considerations . . . . . . . . . . . . . . . . . . . 26 7.1. TLS Extension Type . . . . . . . . . . . . . . . . . . . 30
7.1. Misissued Certificates . . . . . . . . . . . . . . . . . 27 7.2. Hash Algorithms . . . . . . . . . . . . . . . . . . . . . 30
7.2. Detection of Misissue . . . . . . . . . . . . . . . . . . 27 8. Security Considerations . . . . . . . . . . . . . . . . . . . 30
7.3. Redaction of Public Domain Name Labels . . . . . . . . . 27 8.1. Misissued Certificates . . . . . . . . . . . . . . . . . 31
7.4. Misbehaving Logs . . . . . . . . . . . . . . . . . . . . 27 8.2. Detection of Misissue . . . . . . . . . . . . . . . . . . 31
8. Efficiency Considerations . . . . . . . . . . . . . . . . . . 28 8.3. Redaction of Public Domain Name Labels . . . . . . . . . 31
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 28 8.4. Misbehaving Logs . . . . . . . . . . . . . . . . . . . . 31
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 28 8.5. Multiple SCTs . . . . . . . . . . . . . . . . . . . . . . 32
10.1. Normative Reference . . . . . . . . . . . . . . . . . . 28 9. Efficiency Considerations . . . . . . . . . . . . . . . . . . 32
10.2. Informative References . . . . . . . . . . . . . . . . . 29 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 33
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 33
11.1. Normative References . . . . . . . . . . . . . . . . . . 33
11.2. Informative References . . . . . . . . . . . . . . . . . 34
1. Informal Introduction 1. Introduction
Certificate transparency aims to mitigate the problem of misissued Certificate transparency aims to mitigate the problem of misissued
certificates by providing publicly auditable, append-only, untrusted certificates by providing publicly auditable, append-only, untrusted
logs of all issued certificates. The logs are publicly auditable so logs of all issued certificates. The logs are publicly auditable so
that it is possible for anyone to verify the correctness of each log that it is possible for anyone to verify the correctness of each log
and to monitor when new certificates are added to it. The logs do and to monitor when new certificates are added to it. The logs do
not themselves prevent misissue, but they ensure that interested not themselves prevent misissue, but they ensure that interested
parties (particularly those named in certificates) can detect such parties (particularly those named in certificates) can detect such
misissuance. Note that this is a general mechanism, but in this misissuance. Note that this is a general mechanism, but in this
document, we only describe its use for public TLS server certificates document, we only describe its use for public TLS server certificates
issued by public certificate authorities (CAs). issued by public certification authorities (CAs).
Each log consists of certificate chains, which can be submitted by Each log consists of certificate chains, which can be submitted by
anyone. It is expected that public CAs will contribute all their anyone. It is expected that public CAs will contribute all their
newly issued certificates to one or more logs, however certificate newly issued certificates to one or more logs, however certificate
holders can also contribute their own certificate chains, as can holders can also contribute their own certificate chains, as can
third parties. In order to avoid logs being rendered useless by third parties. In order to avoid logs being rendered useless by
submitting large numbers of spurious certificates, it is required submitting large numbers of spurious certificates, it is required
that each chain is rooted in a CA certificate accepted by the log. that each chain is rooted in a CA certificate accepted by the log.
When a chain is submitted to a log, a signed timestamp is returned, When a chain is submitted to a log, a signed timestamp is returned,
which can later be used to provide evidence to TLS clients that the which can later be used to provide evidence to TLS clients that the
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The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119]. document are to be interpreted as described in RFC 2119 [RFC2119].
1.2. Data Structures 1.2. Data Structures
Data structures are defined according to the conventions laid out in Data structures are defined according to the conventions laid out in
Section 4 of [RFC5246]. Section 4 of [RFC5246].
2. Cryptographic Components 2. Cryptographic Components
2.1. Merkle Hash Trees 2.1. Merkle Hash Trees
Logs use a binary Merkle Hash Tree for efficient auditing. The Logs use a binary Merkle Hash Tree for efficient auditing. The
hashing algorithm used by each log is expected to be specified as hashing algorithm used by each log is expected to be specified as
part of the metadata relating to that log. We have established a part of the metadata relating to that log. We have established a
registry of acceptable algorithms, see Section 6.2. The hashing registry of acceptable algorithms, see Section 7.2. The hashing
algorithm in use is referred to as HASH throughout this document. algorithm in use is referred to as HASH throughout this document.
The input to the Merkle Tree Hash is a list of data entries; these The input 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. entries will be hashed to form the leaves of the Merkle Hash Tree.
The output is a single 32-byte Merkle Tree Hash. Given an ordered The output is a single 32-byte Merkle Tree Hash. Given an ordered
list of n inputs, D[n] = {d(0), d(1), ..., d(n-1)}, the Merkle Tree list of n inputs, D[n] = {d(0), d(1), ..., d(n-1)}, the Merkle Tree
Hash (MTH) is thus defined as follows: Hash (MTH) is thus defined as follows:
The hash of an empty list is the hash of an empty string: The hash of an empty list is the hash of an empty string:
MTH({}) = HASH(). MTH({}) = HASH().
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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 either elliptic Various data structures are signed. A log MUST use either elliptic
curve signatures using the NIST P-256 curve (Section D.1.2.3 of the curve signatures using the NIST P-256 curve (Section D.1.2.3 of the
Digital Signature Standard [DSS]) or RSA signatures (RSASSA- Digital Signature Standard [DSS]) or RSA signatures (RSASSA-
PKCS1-V1_5 with SHA-256, Section 8.2 of [RFC3447]) using a key of at PKCS1-v1_5 with SHA-256, Section 8.2 of [RFC3447]) using a key of at
least 2048 bits. least 2048 bits.
3. Log Format and Operation 3. Log Format and Operation
Anyone can submit certificates to certificate logs for public Anyone can submit certificates to certificate logs for public
auditing; however, since certificates will not be accepted by TLS auditing; however, since certificates will not be accepted by TLS
clients unless logged, it is expected that certificate owners or clients unless logged, it is expected that certificate owners or
their CAs will usually submit them. A log is a single, ever-growing, their CAs will usually submit them. A log is a single, ever-growing,
append-only Merkle Tree of such certificates. append-only Merkle Tree of such certificates.
When a valid certificate is submitted to a log, the log MUST return a When a valid certificate is submitted to a log, the log MUST return a
Signed Certificate Timestamp (SCT). The SCT is the log's promise to Signed Certificate Timestamp (SCT). The SCT is the log's promise to
incorporate the certificate in the Merkle Tree within a fixed amount incorporate the certificate in the Merkle Tree within a fixed amount
of time known as the Maximum Merge Delay (MMD). If the log has of time known as the Maximum Merge Delay (MMD). If the log has
previously seen the certificate, it MAY return the same SCT as it previously seen the certificate, it MAY return the same SCT as it
returned before. TLS servers MUST present an SCT from one or more returned before (note that if a certificate was previously logged as
logs to the TLS client together with the certificate. TLS clients a precertificate, then the precertificate's SCT would not be
MUST reject certificates that are not accompanied by an SCT for appropriate, instead a fresh SCT of type x509_entry should be
either the end-entity certificate or for a name-constrained generated). TLS servers MUST present an SCT from one or more logs to
intermediate the end-entity certificate chains to. the TLS client together with the certificate. A certificate not
accompanied by an SCT (either for the end-entity certificate or for a
name-constrained intermediate the end-entity certificate chains to)
MUST NOT be considered compliant by TLS clients.
Periodically, each log appends all its new entries to the Merkle Tree Periodically, each log appends all its new entries to the Merkle Tree
and signs the root of the tree. The log MUST incorporate a and signs the root of the tree. The log MUST incorporate a
certificate in its Merkle Tree within the Maximum Merge Delay period certificate in its Merkle Tree within the Maximum Merge Delay period
after the issuance of the SCT. When encountering an SCT, an Auditor after the issuance of the SCT. When encountering an SCT, an Auditor
can verify that the certificate was added to the Merkle Tree within can verify that the certificate was added to the Merkle Tree within
that timeframe. that timeframe.
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.
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In order to enable attribution of each logged certificate to its In order to enable attribution of each logged certificate to its
issuer, each submitted certificate MUST be accompanied by all issuer, each submitted certificate MUST be accompanied by all
additional certificates required to verify the certificate chain up additional certificates required to verify the certificate chain up
to an accepted root certificate. The root certificate itself MAY be to an accepted root certificate. The root certificate itself MAY be
omitted from the chain submitted to the log server. The log SHALL omitted from the chain submitted to the log server. The log SHALL
allow retrieval of a list of accepted root certificates (this list allow retrieval of a list of accepted root certificates (this list
might usefully be the union of root certificates trusted by major might usefully be the union of root certificates trusted by major
browser vendors). browser vendors).
Alternatively, (root as well as intermediate) certificate authorities Alternatively, (root as well as intermediate) certification
may preannounce a certificate to logs prior to issuance in order to authorities may preannounce a certificate to logs prior to issuance
incorporate the SCT in the issued certificate. To do this, the CA in order to incorporate the SCT in the issued certificate. To do
submits a Precertificate that the log can use to create an entry that this, the CA submits a precertificate that the log can use to create
will be valid against the issued certificate. A Precertificate is a an entry that will be valid against the issued certificate. A
CMS [RFC5652] "signed-data" object that contains a TBSCertificate precertificate is a CMS [RFC5652] "signed-data" object that contains
[RFC5280] in its "SignedData.encapContentInfo.eContent" field, a TBSCertificate [RFC5280] in its
identified by the OID <TBD> in the "SignedData.encapContentInfo.eContent" field, identified by the OID
"SignedData.encapContentInfo.eContentType" field. This <TBD> in the "SignedData.encapContentInfo.eContentType" field. This
TBSCertificate MAY redact certain domain name labels that will be TBSCertificate MAY redact certain domain name labels that will be
present in the issued certificate (see Section 3.2.2) and MUST NOT present in the issued certificate (see Section 3.2.2) and MUST NOT
contain any SCTs, but it will be otherwise identical to the contain any SCTs, but it will be otherwise identical to the
TBSCertificate in the issued certificate. "SignedData.signerInfos" TBSCertificate in the issued certificate. "SignedData.signerInfos"
MUST contain a signature from the same (root or intermediate) CA that MUST contain a signature from the same (root or intermediate) CA that
will ultimately issue the certificate. This signature indicates the will ultimately issue the certificate. This signature indicates the
certificate authority's intent to issue the certificate. This intent certification authority's intent to issue the certificate. This
is considered binding (i.e., misissuance of the Precertificate is intent is considered binding (i.e., misissuance of the precertificate
considered equivalent to misissuance of the certificate). As above, is considered equivalent to misissuance of the certificate). As
the Precertificate submission MUST be accompanied by all the above, the precertificate submission MUST be accompanied by all the
additional certificates required to verify the chain up to an additional certificates required to verify the chain up to an
accepted root certificate. This does not involve using the accepted root certificate. This does not involve using the
"SignedData.certificates" field, so that field SHOULD be omitted. "SignedData.certificates" field, so that field SHOULD be omitted.
Logs MUST verify that the submitted certificate or Precertificate has Logs MUST verify that the submitted certificate or precertificate has
a valid signature chain to an accepted root certificate, using the a valid signature chain to an accepted root certificate, using the
chain of intermediate CA certificates provided by the submitter. chain of intermediate CA certificates provided by the submitter.
Logs MAY accept certificates and Precertificates that have expired, Logs MUST accept certificates that are fully valid according to X.509
are not yet valid, have been revoked, or are otherwise not fully verification rules and are submitted with such a chain. Logs MAY
valid according to X.509 verification rules in order to accommodate accept certificates and precertificates that have expired, are not
quirks of CA certificate-issuing software. However, logs MUST reject yet valid, have been revoked, or are otherwise not fully valid
according to X.509 verification rules in order to accommodate quirks
of CA certificate-issuing software. However, logs MUST reject
certificates without a valid signature chain to an accepted root certificates without a valid signature chain to an accepted root
certificate. If a certificate is accepted and an SCT issued, the certificate. If a certificate is accepted and an SCT issued, the
accepting log MUST store the entire chain used for verification, accepting log MUST store the entire chain used for verification,
including the certificate or Precertificate itself and including the including the certificate or precertificate itself and including the
root certificate used to verify the chain (even if it was omitted root certificate used to verify the chain (even if it was omitted
from the submission), and MUST present this chain for auditing upon from the submission), and MUST present this chain for auditing upon
request. This chain is required to prevent a CA from avoiding blame request. This chain is required to prevent a CA from avoiding blame
by logging a partial or empty chain. (Note: This effectively by logging a partial or empty chain. (Note: This effectively
excludes self-signed and DANE-based certificates until some mechanism excludes self-signed and DANE-based certificates until some mechanism
to limit the submission of spurious certificates is found. The to limit the submission of spurious certificates is found. The
authors welcome suggestions.) authors welcome suggestions.)
Each certificate or precertificate entry in a log MUST include the
Each certificate or Precertificate entry in a log MUST include the
following components: following components:
enum { x509_entry(0), precert_entry_V2(3), (65535) } LogEntryType; enum { x509_entry(0), precert_entry_V2(3), (65535) } LogEntryType;
struct { struct {
LogEntryType entry_type; LogEntryType entry_type;
select (entry_type) { select (entry_type) {
case x509_entry: X509ChainEntry; case x509_entry: X509ChainEntry;
case precert_entry_V2: PrecertChainEntryV2; case precert_entry_V2: PrecertChainEntryV2;
} entry; } entry;
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"leaf_certificate" is the end-entity certificate submitted for "leaf_certificate" is the end-entity certificate submitted for
auditing. auditing.
"certificate_chain" is a chain of additional certificates required to "certificate_chain" is a chain of additional certificates required to
verify the end-entity certificate. The first certificate MUST verify the end-entity certificate. The first certificate MUST
certify the end-entity certificate. Each following certificate MUST certify the end-entity 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
either be, or be issued by, a root certificate accepted by the log. either be, or be issued by, a root certificate accepted by the log.
"pre_certificate" is the Precertificate submitted for auditing. "pre_certificate" is the precertificate submitted for auditing.
"precertificate_chain" is a chain of additional certificates required "precertificate_chain" is a chain of additional certificates required
to verify the Precertificate submission. The first certificate MUST to verify the precertificate submission. The first certificate MUST
certify the Precertificate. Each following certificate MUST directly certify the precertificate. Each following certificate MUST directly
certify the one preceding it. The final certificate MUST be a root certify the one preceding it. The final certificate MUST be a root
certificate accepted by the log. certificate accepted by the log.
3.2. Private Domain Name Labels 3.2. Private Domain Name Labels
Some regard some DNS domain name labels within their registered Some regard some DNS domain name labels within their registered
domain space as private and security sensitive. Even though these domain space as private and security sensitive. Even though these
domains are often only accessible within the domain owner's private domains are often only accessible within the domain owner's private
network, it's common for them to be secured using publicly trusted network, it's common for them to be secured using publicly trusted
TLS server certificates. We define a mechanism to allow these TLS server certificates. We define a mechanism to allow these
skipping to change at page 12, line 29 skipping to change at page 12, line 31
Since TLS clients only match the wildcard character to the complete Since TLS clients only match the wildcard character to the complete
leftmost label of the DNS domain name (see Section 6.4.3 of leftmost label of the DNS domain name (see Section 6.4.3 of
[RFC6125]), this approach would not work for a DNS-ID such as [RFC6125]), this approach would not work for a DNS-ID such as
"top.secret.example.com". Also, wildcard certificates are prohibited "top.secret.example.com". Also, wildcard certificates are prohibited
in some cases, such as Extended Validation Certificates in some cases, such as Extended Validation Certificates
[EVSSLGuidelines]. [EVSSLGuidelines].
3.2.2. Redacting Domain Name Labels in Precertificates 3.2.2. Redacting Domain Name Labels in Precertificates
When creating a Precertificate, the CA MAY substitute one or more of When creating a precertificate, the CA MAY substitute one or more
the complete leftmost labels in each DNS-ID with the literal string labels in each DNS-ID with a corresponding number of "?" labels.
"(PRIVATE)". For example, if a certificate contains a DNS-ID of Every label to the left of a "?" label MUST also be redacted. For
"top.secret.example.com", then the corresponding Precertificate could example, if a certificate contains a DNS-ID of
contain "(PRIVATE).example.com" instead. Labels in a CN-ID [RFC6125] "top.secret.example.com", then the corresponding precertificate could
MUST remain unredacted. contain "?.?.example.com" instead, but not "top.?.example.com"
instead.
When a Precertificate contains one or more redacted labels, a non- Wildcard "*" labels MUST NOT be redacted. However, if the complete
leftmost label of a DNS-ID is "*", it is considered redacted for the
purposes of determining if the label to the right may be redacted.
For example, if a certificate contains a DNS-ID of
"*.top.secret.example.com", then the corresponding precertificate
could contain "*.?.?.example.com" instead, but not
"?.?.?.example.com" instead.
When a precertificate contains one or more redacted labels, a non-
critical extension (OID 1.3.6.1.4.1.11129.2.4.6, whose extnValue critical extension (OID 1.3.6.1.4.1.11129.2.4.6, whose extnValue
OCTET STRING contains an ASN.1 SEQUENCE OF INTEGERs) MUST be added to OCTET STRING contains an ASN.1 SEQUENCE OF INTEGERs) MUST be added to
the corresponding certificate: the first INTEGER indicates the number the corresponding certificate: the first INTEGER indicates the total
of labels redacted in the Precertificate's first DNS-ID; the second number of redacted labels and wildcard "*" labels in the
INTEGER does the same for the Precertificate's second DNS-ID; etc. precertificate's first DNS-ID; the second INTEGER does the same for
There MUST NOT be more INTEGERs than there are DNS-IDs. If there are the precertificate's second DNS-ID; etc. There MUST NOT be more
fewer INTEGERs than there are DNS-IDs, the shortfall is made up by INTEGERs than there are DNS-IDs. If there are fewer INTEGERs than
implicitly repeating the last INTEGER. Each INTEGER MUST have a there are DNS-IDs, the shortfall is made up by implicitly repeating
value of zero or more. The purpose of this extension is to enable the last INTEGER. Each INTEGER MUST have a value of zero or more.
TLS clients to accurately reconstruct the Precertificate from the The purpose of this extension is to enable TLS clients to accurately
certificate without having to perform any guesswork. reconstruct the TBSCertificate component of the precertificate from
the certificate without having to perform any guesswork.
When a precertificate contains that extension and contains a CN-ID
[RFC6125], the CN-ID MUST match the first DNS-ID and have the same
labels redacted. TLS clients will use the first entry in the
SEQUENCE OF INTEGERs to reconstruct both the first DNS-ID and the CN-
ID.
3.2.3. Using a Name-Constrained Intermediate CA 3.2.3. Using a Name-Constrained Intermediate CA
An intermediate CA certificate or intermediate CA Precertificate that An intermediate CA certificate or intermediate CA precertificate that
contains the critical or non-critical Name Constraints [RFC5280] contains the critical or non-critical Name Constraints [RFC5280]
extension MAY be logged in place of end-entity certificates issued by extension MAY be logged in place of end-entity certificates issued by
that intermediate CA, as long as all of the following conditions are that intermediate CA, as long as all of the following conditions are
met: met:
o there MUST be a non-critical extension (OID o there MUST be a non-critical extension (OID
1.3.6.1.4.1.11129.2.4.7, whose extnValue OCTET STRING contains 1.3.6.1.4.1.11129.2.4.7, whose extnValue OCTET STRING contains
ASN.1 NULL data (0x05 0x00)). This extension is an explicit ASN.1 NULL data (0x05 0x00)). This extension is an explicit
indication that it is acceptable to not log certificates issued by indication that it is acceptable to not log certificates issued by
this intermediate CA. this intermediate CA.
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} LogID; } LogID;
opaque TBSCertificate<1..2^24-1>; opaque TBSCertificate<1..2^24-1>;
opaque CtExtensions<0..2^16-1>; opaque CtExtensions<0..2^16-1>;
"key_id" is the SHA-256 hash of the log's public key, calculated over "key_id" is the SHA-256 hash of the log's public key, calculated over
the DER encoding of the key represented as SubjectPublicKeyInfo. the DER encoding of the key represented as SubjectPublicKeyInfo.
"tbs_certificate" is the DER-encoded TBSCertificate component of the "tbs_certificate" is the DER-encoded TBSCertificate component of the
Precertificate. Note that it is also possible to reconstruct this precertificate. Note that it is also possible to reconstruct this
TBSCertificate from the issued certificate by extracting the TBSCertificate from the issued certificate by extracting the
TBSCertificate from it, redacting the domain name labels indicated by TBSCertificate from it, redacting the domain name labels indicated by
the redacted labels extension, and deleting the SCT list extension the redacted labels extension, and deleting the SCT list extension
and redacted labels extension. and redacted labels extension.
struct { struct {
Version sct_version; Version sct_version;
LogID id; LogID id;
uint64 timestamp; uint64 timestamp;
CtExtensions extensions; CtExtensions extensions;
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(see [RFC2560]) and body: (see [RFC2560]) and body:
SignedCertificateTimestampList ::= OCTET STRING SignedCertificateTimestampList ::= OCTET STRING
in the singleExtensions component of the SingleResponse pertaining to in the singleExtensions component of the SingleResponse pertaining to
the end-entity certificate. the end-entity certificate.
At least one SCT MUST be included. Server operators MAY include more At least one SCT MUST be included. Server operators MAY include more
than one SCT. than one SCT.
Similarly, a certificate authority MAY submit a Precertificate to Similarly, a certification authority MAY submit a precertificate to
more than one log, and all obtained SCTs can be directly embedded in more than one log, and all obtained SCTs can be directly embedded in
the issued certificate, by encoding the the issued certificate, by encoding the
SignedCertificateTimestampList structure as an ASN.1 OCTET STRING and SignedCertificateTimestampList structure as an ASN.1 OCTET STRING and
inserting the resulting data in the TBSCertificate as a non-critical inserting the resulting data in the TBSCertificate as a non-critical
X.509v3 certificate extension (OID 1.3.6.1.4.1.11129.2.4.2). Upon X.509v3 certificate extension (OID 1.3.6.1.4.1.11129.2.4.2). Upon
receiving the certificate, clients can reconstruct the original receiving the certificate, clients can reconstruct the original
TBSCertificate to verify the SCT signature. TBSCertificate to verify the SCT signature.
The contents of the ASN.1 OCTET STRING embedded in an OCSP extension The contents of the ASN.1 OCTET STRING embedded in an OCSP extension
or X509v3 certificate extension are as follows: or X509v3 certificate extension are as follows:
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TLS clients MUST implement all three mechanisms. Servers MUST TLS clients MUST implement all three mechanisms. Servers MUST
implement at least one of the three mechanisms. Note that existing implement at least one of the three mechanisms. Note that existing
TLS servers can generally use the certificate extension mechanism TLS servers can generally use the certificate extension mechanism
without modification. without modification.
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 client (for example, if a log has been logs are not acceptable to the client (for example, if a log has been
struck off for misbehavior, has had a key compromise or is not known struck off for misbehavior, has had a key compromise or is not known
to the client). to the client).
The three mechanisms are provided because they have different
tradeoffs. Embedding the SCTs in the certificate allows the use of
unmodified TLS servers, but, because they cannot be changed without
re-issuing the certificate, increases the risk that the certificate
will be refused if the SCTs become invalid. OCSP Stapling is already
widely (but not universally) implemented, and provides a mechanism by
which TLS servers that already support it can serve SCTs that are
generated on the fly. Finally, the TLS extension permits TLS servers
to participate in CT without the cooperation of CAs, unlike the other
two mechanisms. It also allows SCTs to be updated on the fly.
3.4.1. TLS Extension 3.4.1. TLS Extension
The SCT can be sent during the TLS handshake using a TLS extension The SCT can be sent during the TLS handshake using a TLS extension
with type "signed_certificate_timestamp". with type "signed_certificate_timestamp".
Clients that support the extension SHOULD send a ClientHello Clients that support the extension SHOULD send a ClientHello
extension with the appropriate type and empty "extension_data". extension with the appropriate type and empty "extension_data".
Servers MUST only send SCTs to clients who have indicated support for Servers MUST only send SCTs in this TLS extension to clients who have
the extension in the ClientHello, in which case the SCTs are sent by indicated support for the extension in the ClientHello, in which case
setting the "extension_data" to a "SignedCertificateTimestampList". the SCTs are sent by setting the "extension_data" to a
"SignedCertificateTimestampList".
Session resumption uses the original session information: clients Session resumption uses the original session information: clients
SHOULD include the extension type in the ClientHello, but if the SHOULD include the extension type in the ClientHello, but if the
session is resumed, the server is not expected to process it or session is resumed, the server is not expected to process it or
include the extension in the ServerHello. include the extension in the ServerHello.
3.5. Merkle Tree 3.5. Merkle Tree
The hashing algorithm for the Merkle Tree Hash is specified in the The hashing algorithm for the Merkle Tree Hash is specified in the
log's metadata. log's metadata.
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Structure of the Merkle Tree input: Structure of the Merkle Tree input:
enum { v1(0), v2(1), (255) } enum { v1(0), v2(1), (255) }
LeafVersion; LeafVersion;
struct { struct {
uint64 timestamp; uint64 timestamp;
LogEntryType entry_type; LogEntryType entry_type;
select(entry_type) { select(entry_type) {
case x509_entry: ASN.1Cert; case x509_entry: ASN.1Cert;
case precert_entry_V2: PreCert; case precert_entry_V2: TBSCertificate;
} signed_entry; } signed_entry;
CtExtensions extensions; CtExtensions extensions;
} TimestampedEntry; } TimestampedEntry;
struct { struct {
LeafVersion version; LeafVersion version;
TimestampedEntry timestamped_entry; TimestampedEntry timestamped_entry;
} MerkleTreeLeaf; } MerkleTreeLeaf;
Here, "version" is the version of the MerkleTreeLeaf structure. This Here, "version" is the version of the MerkleTreeLeaf structure. This
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The leaves of the Merkle Tree are the leaf hashes of the The leaves of the Merkle Tree are the leaf hashes of the
corresponding "MerkleTreeLeaf" structures. corresponding "MerkleTreeLeaf" structures.
3.6. Signed Tree Head 3.6. Signed Tree Head
Every time a log appends new entries to the tree, the log SHOULD sign Every time a log appends new entries to the tree, the log SHOULD sign
the corresponding tree hash and tree information (see the the corresponding tree hash and tree information (see the
corresponding Signed Tree Head client message in Section 4.3). The corresponding Signed Tree Head client message in Section 4.3). The
signature for that data is structured as follows: signature for that data is structured as follows:
opaque CtSthExtensions<0..2^16-1>; enum { v1(0), (255) } TreeHeadVersion;
enum { v1(0), v2(1), (255) }
TreeHeadVersion;
digitally-signed struct { digitally-signed struct {
TreeHeadVersion version; TreeHeadVersion version;
SignatureType signature_type = tree_hash; SignatureType signature_type = tree_hash;
uint64 timestamp; uint64 timestamp;
uint64 tree_size; uint64 tree_size;
opaque sha256_root_hash[32]; opaque sha256_root_hash[32];
CtSthExtensions extensions; } TreeHeadSignature;
} TreeHeadSignature;
"version" is the version of the TreeHeadSignature structure. This "version" is the version of the TreeHeadSignature structure. This
version is v2. version is v1.
"timestamp" is the current time. The timestamp MUST be at least as "timestamp" is the current time. The timestamp MUST be at least as
recent as the most recent SCT timestamp in the tree. Each subsequent recent as the most recent SCT timestamp in the tree. Each subsequent
timestamp MUST be more recent than the timestamp of the previous timestamp MUST be more recent than the timestamp of the previous
update. update.
"tree_size" equals the number of entries in the new tree. "tree_size" equals the number of entries in the new tree.
"sha256_root_hash" is the root of the Merkle Hash Tree. "sha256_root_hash" is the root of the Merkle Hash Tree.
"extensions" are future extensions to TreeHeadSignature v2.
Currently, no extensions are specified. Note that TreeHeadSignature
v1 [RFC6962] does not include this field. The purpose of the
"extensions" field is to allow augmenting the TreeHeadSignature
without increasing its version.
Each log MUST produce on demand a Signed Tree Head that is no older Each log MUST produce on demand a Signed Tree Head that is no older
than the Maximum Merge Delay. In the unlikely event that it receives than the Maximum Merge Delay. In the unlikely event that it receives
no new submissions during an MMD period, the log SHALL sign the same no new submissions during an MMD period, the log SHALL sign the same
Merkle Tree Hash with a fresh timestamp. Merkle Tree Hash with a fresh timestamp.
4. Log Client Messages 4. 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 [RFC4627]. Parameters for GETs are encoded as order- (JSON) objects [RFC4627]. Parameters for GETs are encoded as order-
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Note that JSON objects and URL parameters may contain fields not Note that JSON objects and URL parameters may contain fields not
specified here. These extra fields should be ignored. specified here. These extra fields should be ignored.
The <log server> prefix MAY include a path as well as a server name The <log server> prefix MAY include a path as well as a server name
and a port. and a port.
In general, where needed, the "version" is v1 and the "id" is the log In general, where needed, the "version" is v1 and the "id" is the log
id for the log server queried. id for the log server queried.
In practice, log servers may include multiple front-end machines.
Since it is impractical to keep these machines in perfect sync,
errors may occur that are caused by skew between the machines. Where
such errors are possible, the front-end will return additional
information (as specified below) making it possible for clients to
make progress, if progress is possible. Front-ends MUST only serve
data that is free of gaps (that is, for example, no front-end will
respond with an STH unless it is also able to prove consistency from
all log entries logged within that STH).
For example, when a consistency proof between two STHs is requested,
the front-end reached may not yet be aware of one or both STHs. In
the case where it is unaware of both, it will return the latest STH
it is aware of. Where it is aware of the first but not the second,
it will return the latest STH it is aware of and a consistency proof
from the first STH to the returned STH. The case where it knows the
second but not the first should not arise (see the "no gaps"
requirement above).
If the log is unable to process a client's request, it MUST return an If the log is unable to process a client's request, it MUST return an
HTTP response code of 4xx/5xx (see [RFC2616]), and, in place of the HTTP response code of 4xx/5xx (see [RFC2616]), and, in place of the
responses outlined in the subsections below, the body SHOULD be a responses outlined in the subsections below, the body SHOULD be a
JSON structure containing at least the following field: JSON structure containing at least the following field:
error_message: error_message: A human-readable string describing the error which
prevented the log from processing the request.
A human-readable string describing the error which prevented In the case of a malformed request, the string SHOULD provide
the log from processing the request. sufficient detail for the error to be rectified.
In the case of a malformed request, the string SHOULD provide error_code: An error code readable by the client. Some codes are
sufficient detail for the error to be rectified. generic and are detailed here. Others are detailed in the
individual requests. Error codes are fixed text strings.
not compliant The request is not compliant with this RFC.
e.g. In response to a request of "/ct/v1/get- e.g. In response to a request of "/ct/v1/get-
entries?start=100&end=99", the log would return a "400 Bad Request" entries?start=100&end=99", the log would return a "400 Bad Request"
response code with a body similar to the following: response code with a body similar to the following:
{ {
"error_message": "'start' cannot be greater than 'end'", "error_message": "'start' cannot be greater than 'end'",
"error_code": "not compliant",
} }
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
[RFC2616], in the case of a 503 response the log MAY include a [RFC2616], 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.
4.1. Add Chain to Log 4.1. Add Chain to Log
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timestamp: The SCT timestamp, in decimal. timestamp: The SCT timestamp, in decimal.
extensions: An opaque type for future expansion. It is likely extensions: An opaque type for future expansion. It is likely
that not all participants will need to understand data in this that not all participants will need to understand data in this
field. Logs should set this to the empty string. Clients field. Logs should set this to the empty string. Clients
should decode the base64-encoded data and include it in the should decode the base64-encoded data and include it in the
SCT. SCT.
signature: The SCT signature, base64 encoded. signature: The SCT signature, base64 encoded.
Error codes:
unknown root The root of the chain is not one accepted by the
log.
bad chain The alleged chain is not actually a chain of
certificates.
bad certificate One or more certificates in the chain are not
valid (e.g. not properly encoded).
If the "sct_version" is not v1, then a v1 client may be unable to If the "sct_version" is not v1, then a v1 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 v1 clients that do not is to avoid forcing an upgrade of compliant v1 clients that do not
use the returned SCTs. use the returned SCTs.
If a log detects bad encoding in a chain that otherwise verifies
correctly (e.g. some software will accept BER instead of DER
encodings in certificates, or incorrect character encodings, even
though these are technically incorrect) then the log MAY still log
the certificate but SHOULD NOT return an SCT. It should instead
return the "bad certificate" error. Logging the certificate is
useful, because monitors can then detect these encoding errors, which
may be accepted by some TLS clients.
Note that not all certificate handling software is capable of
detecting all encoding errors.
4.2. Add PreCertChain to Log 4.2. Add PreCertChain to Log
POST https://<log server>/ct/v1/add-pre-chain POST https://<log server>/ct/v1/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 chains element is the signer of the precertificate; the second chains
to the first and so on to the last, which is either the root to the first and so on to the last, which is either the root
certificate or a certificate that chains to an accepted root certificate or a certificate that chains to an accepted root
certificate. certificate.
Outputs are the same as in Section 4.1. Outputs and errors are the same as in Section 4.1.
4.3. Retrieve Latest Signed Tree Head 4.3. Retrieve Latest Signed Tree Head
GET https://<log server>/ct/v1/get-sth GET https://<log server>/ct/v1/get-sth
No inputs. No inputs.
Outputs: Outputs:
tree_size: The size of the tree, in entries, in decimal. tree_size: The size of the tree, in entries, in decimal.
timestamp: The timestamp, in decimal. timestamp: The timestamp, in decimal.
sha256_root_hash: The Merkle Tree Hash of the tree, in base64. sha256_root_hash: The Merkle Tree Hash of the tree, in base64.
tree_head_signature: A TreeHeadSignature for the above data. tree_head_signature: A TreeHeadSignature for the above data.
4.4. Retrieve Merkle Consistency Proof between Two Signed Tree Heads 4.4. Retrieve Merkle Consistency Proof between Two Signed Tree Heads
GET https://<log server>/ct/v1/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. second: The tree_size of the newer tree, in decimal (optional).
Both tree sizes must be from existing v1 STHs (Signed Tree Heads). Both tree sizes must be from existing v1 STHs (Signed Tree Heads).
However, because of skew, the receiving front-end may not know one
or both of the existing STHs. If both are known, then only the
"consistency" output is returned. If the first is known but the
second is not (or has been omitted), then the latest known STH is
returned, along with a consistency proof between the first STH and
the latest. If neither are known, then the latest known STH is
returned without a consistency proof.
Outputs: Outputs:
consistency: An array of Merkle Tree nodes, base64 encoded. consistency: An array of Merkle Tree nodes, base64 encoded.
Note that no signature is required on this data, as it is used to tree_size: The size of the tree, in entries, in decimal.
verify an STH, which is signed.
timestamp: The timestamp, in decimal.
sha256_root_hash: The Merkle Tree Hash of the tree, in base64.
tree_head_signature: A TreeHeadSignature for the above data.
Note that no signature is required on this data, as it is used to
verify an STH, which is signed.
Error codes:
first unknown "first" is before the latest known STH but is not
from an existing STH.
second unknown "second" is before the latest known STH but is not
from an existing STH.
4.5. Retrieve Merkle Inclusion Proof from Log by Leaf Hash 4.5. Retrieve Merkle Inclusion Proof from Log by Leaf Hash
GET https://<log server>/ct/v1/get-proof-by-hash GET https://<log server>/ct/v2/get-proof-by-hash
Inputs: Inputs:
hash: A base64-encoded v1 leaf hash. hash: A base64-encoded v1 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 3.5. The The "hash" must be calculated as defined in Section 3.5. The
"tree_size" must designate an existing v1 STH. "tree_size" must designate an existing v1 STH. Because of skew,
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
to that STH. If the front-end knows the requested STH then only
"leaf_index" and "audit_path" are returned.
Outputs: Outputs:
leaf_index: The 0-based index of the entry corresponding to the leaf_index: The 0-based index of the entry corresponding to the
"hash" parameter. "hash" parameter.
audit_path: An array of base64-encoded Merkle Tree nodes proving audit_path: An array of base64-encoded Merkle Tree nodes proving
the inclusion of the chosen certificate. the inclusion of the chosen certificate.
4.6. Retrieve Entries from Log tree_size: The size of the tree, in entries, in decimal.
timestamp: The timestamp, in decimal.
sha256_root_hash: The Merkle Tree Hash of the tree, in base64.
tree_head_signature: A TreeHeadSignature for the above data.
Error codes:
hash unknown "hash" is not the hash of a known leaf (may be
caused by skew or by a known certificate not yet merged).
tree_size unknown "hash" is before the latest known STH but is
not from an existing STH.
4.6. Retrieve Merkle Inclusion Proof, Signed Tree Head and Consistency
Proof by Leaf Hash
GET https://<log server>/ct/v2/get-all-by-hash
Inputs:
hash: A base64-encoded v1 leaf hash.
tree_size: The tree_size of the tree on which to base the proofs,
in decimal.
The "hash" must be calculated as defined in Section 3.5. The
"tree_size" must designate an existing v1 STH.
Because of skew, the front-end may not know the requested STH or
the requested hash, which leads to a number of cases.
latest STH < requested STH Return latest STH.
latest STH > requested STH Return latest STH and a consistency
proof between it and the requested STH (see Section 4.4).
index of requested hash < latest STH Return "leaf_index" and
"audit_path".
Note that more than one case can be true, in which case the
returned data is their concatenation. It is also possible for
none to be true, in which case the front-end MUST return an empty
response.
Outputs:
leaf_index: The 0-based index of the entry corresponding to the
"hash" parameter.
audit_path: An array of base64-encoded Merkle Tree nodes proving
the inclusion of the chosen certificate.
tree_size: The size of the tree, in entries, in decimal.
timestamp: The timestamp, in decimal.
sha256_root_hash: The Merkle Tree Hash of the tree, in base64.
tree_head_signature: A TreeHeadSignature for the above data.
consistency: An array of base64-encoded Merkle Tree nodes proving
the consistency of the requested STH and the returned STH.
Errors are the same as in Section 4.5.
4.7. Retrieve Entries from Log
GET https://<log server>/ct/v1/get-entries GET https://<log server>/ct/v1/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:
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"tree_size" by returning a partial response covering only the valid "tree_size" by returning a partial response covering only the valid
entries in the specified range. Note that the following restriction entries in the specified range. Note that the following restriction
may also apply: may also apply:
Logs MAY restrict the number of entries that can be retrieved per Logs MAY restrict the number of entries that can be retrieved per
"get-entries" request. If a client requests more than the permitted "get-entries" request. If a client requests more than the permitted
number of entries, the log SHALL return the maximum number of entries number of entries, the log SHALL return the maximum number of entries
permissible. These entries SHALL be sequential beginning with the permissible. These entries SHALL be sequential beginning with the
entry specified by "start". entry specified by "start".
4.7. Retrieve Accepted Root Certificates 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
empty "entries" array.
4.8. Retrieve Accepted Root Certificates
GET https://<log server>/ct/v1/get-roots GET https://<log server>/ct/v1/get-roots
No inputs. No inputs.
Outputs: Outputs:
certificates: An array of base64-encoded root certificates that certificates: An array of base64-encoded root certificates that
are acceptable to the log. are acceptable to the log.
4.8. Retrieve Entry+Merkle Inclusion Proof from Log max_chain: If the server has chosen to limit the length of chains
it accepts, this is the maximum number of certificates in the
GET https://<log server>/ct/v1/get-entry-and-proof chain, in decimal. If there is no limit, this is omitted.
Inputs:
leaf_index: The index of the desired entry.
tree_size: The tree_size of the tree for which the proof is
desired.
The tree size must designate an existing STH.
Outputs:
leaf_input: The base64-encoded MerkleTreeLeaf structure.
extra_data: The base64-encoded unsigned data, same as in
Section 4.6.
audit_path: An array of base64-encoded Merkle Tree nodes proving
the inclusion of the chosen certificate.
This API is probably only useful for debugging.
5. Clients 5. 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 could function. We describe here some typical clients and how they could 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
and verify their responses. This metadata is described below, but
note that this document does not describe how the metadata is
obtained, which is implementation dependent (see, for example,
[Chromium.Policy]).
Clients should somehow exchange STHs they see, or make them available Clients should somehow exchange STHs they see, or make them available
for scrutiny, in order to ensure that they all have a consistent for scrutiny, in order to ensure that they all have a consistent
view. The exact mechanisms will be in separate documents, but it is view. The exact mechanisms will be in separate documents, but it is
expected there will be a variety. expected there will be a variety.
5.1. Submitters 5.1. Metadata
Submitters submit certificates or Precertificates to the log as In order to communicate with and verify a log, clients need metadata
about the log.
Base URL: The URL to substitute for <log server> in Section 4.
Hash Algorithm The hash algorithm used for the Merkle Tree (see
Section 7.2).
Signing Algorithm The signing algorithm used (see Section 2.1.4).
Public Key The public key used for signing.
Maximum Merge Delay The MMD the log has committed to.
Final STH If a log has been closed down (i.e. no longer accepts new
entries), existing entries may still be valid. In this case, the
client should know the final valid STH in the log to ensure no new
entries can be added without detection.
[JSON.Metadata] is an example of a metadata format which includes the
above elements.
5.2. Submitters
Submitters submit certificates or precertificates to the log as
described above. When a Submitter intends to use the returned SCT described above. When a Submitter intends to use the returned SCT
directly in a TLS handshake or to construct a certificate, they directly in a TLS handshake or to construct a certificate, they
SHOULD validate the SCT as described in Section 5.2 if they SHOULD validate the SCT as described in Section 5.3 if they
understand its format. understand its format.
5.2. TLS Client 5.3. TLS Client
TLS clients receive SCTs alongside or in certificates, either for the TLS clients receive SCTs alongside or in certificates, either for the
server certificate itself or for intermediate CA Precertificates. In server certificate itself or for intermediate CA precertificates. In
addition to normal validation of the certificate and its chain, TLS addition to normal validation of the certificate and its chain, TLS
clients SHOULD validate the SCT by computing the signature input from clients SHOULD validate the SCT by computing the signature input from
the SCT data as well as the certificate and verifying the signature, the SCT data as well as the certificate and verifying the signature,
using the corresponding log's public key. TLS clients MAY audit the using the corresponding log's public key.
corresponding log by requesting, and verifying, a Merkle audit proof
for said certificate. Note that this document does not describe how A TLS client MAY audit the corresponding log by requesting, and
clients obtain the logs' public keys or URLs. verifying, a Merkle audit proof for said certificate. 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 4.3), then verify
it by requesting a consistency proof (Section 4.4).
TLS clients MUST reject SCTs whose timestamp is in the future. TLS clients MUST reject SCTs whose timestamp is in the future.
5.3. Monitor 5.4. Monitor
Monitors watch logs and check that they behave correctly. They also Monitors watch logs and check that they behave correctly. Monitors
watch for certificates of interest. may additionally watch for certificates of interest. For example, a
monitor may be configured to report on all certificates that apply to
a specific 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 4.3). 1. Fetch the current STH (Section 4.3).
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 4.6). (Section 4.7).
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 4.3). Repeat until the STH 5. Fetch the current STH (Section 4.3). 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 4.6). If they remain unavailable for an extended (Section 4.7). 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 4.4). STH (Section 4.4).
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.
5.4. Auditor 5.5. Auditing
Auditors take partial information about a log as input and verify Auditing is taking partial information about a log as input and
that this information is consistent with other partial information verifying that this information is consistent with other partial
they have. An auditor might be an integral component of a TLS information held. All clients described above may perform auditing
client; it might be a standalone service; or it might be a secondary as an additional function. The action taken by the client if audit
function of a monitor. fails is not specified, but note that in general if audit fails, the
client is in possession of signed proof of the log's misbehavior.
Any pair of STHs from the same log can be verified by requesting a A monitor (Section 5.4) can audit by verifying the consistency of
consistency proof (Section 4.4). 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.
A certificate accompanied by an SCT can be verified against any STH A TLS client (Section 5.3) can audit by verifying an SCT against any
dated after the SCT timestamp + the Maximum Merge Delay by requesting STH dated after the SCT timestamp + the Maximum Merge Delay by
a Merkle inclusion proof (Section 4.5). requesting a Merkle inclusion proof (Section 4.5). It can also
verify that the SCT corresponds to the certificate it arrived with
(i.e. the log entry is that certificate, is a precertificate for that
certificate or is an appropriate name-constrained intermediate [see
Section 3.2.3]).
Auditors can fetch STHs from time to time of their own accord, of 6. Algorithm Agility
course (Section 4.3).
6. IANA Considerations It is not possible for a log to change any of its algorithms part way
through its lifetime. If it should become necessary to deprecate an
algorithm used by a live log, then the log should be frozen as
specified in Section 5.1 and a new log should be started. If
necessary, the new log can contain existing entries from the frozen
log, which monitors can verify are an exact match.
6.1. TLS Extension Type 7. IANA Considerations
7.1. TLS Extension Type
IANA has allocated an RFC 5246 ExtensionType value (18) for the SCT IANA has allocated an RFC 5246 ExtensionType value (18) for the SCT
TLS extension. The extension name is "signed_certificate_timestamp". TLS extension. The extension name is "signed_certificate_timestamp".
IANA should update this extension type to point at this document. IANA should update this extension type to point at this document.
6.2. Hash Algorithms 7.2. Hash Algorithms
IANA is asked to establish a registry of hash values, initially IANA is asked to establish a registry of hash values, initially
consisting of: consisting of:
+-------+----------------------+ +-------+----------------------+
| Index | Hash | | Index | Hash |
+-------+----------------------+ +-------+----------------------+
| 0 | SHA-256 [FIPS.180-4] | | 0 | SHA-256 [FIPS.180-4] |
+-------+----------------------+ +-------+----------------------+
7. Security Considerations 8. 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 the subject of the certificate has had this, the client knows that the subject of the certificate has had
some time to notice the misissue and take some action, such as asking some time to notice the misissue and take some action, such as asking
a CA to revoke a misissued certificate, or that the log has a CA to revoke a misissued certificate, or that the log has
misbehaved, which will be discovered when the SCT is audited. A misbehaved, which will be discovered when the SCT is audited. A
signed timestamp is not a guarantee that the certificate is not signed timestamp is not a guarantee that the certificate is not
misissued, since the subject of the certificate might not have misissued, since the subject of the certificate might not have
checked the logs or the CA might have refused to revoke the checked the logs or the CA might have refused to revoke the
certificate. 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.
7.1. Misissued Certificates 8.1. 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, will be rejected by TLS clients. Misissued do not have a valid SCT, will be rejected by TLS clients. 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.
7.2. Detection of Misissue 8.2. 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.
7.3. Redaction of Public Domain Name Labels 8.3. Redaction of Public Domain Name Labels
CAs SHOULD NOT redact domain name labels in Precertificates to the CAs SHOULD NOT redact domain name labels in precertificates such that
extent that domain name ownership becomes unclear (e.g. the entirety of the domain space below the unredacted part of the
"(PRIVATE).com" and "(PRIVATE).co.uk" would both be problematic). domain name is not owned or controlled by a single entity (e.g.
Logs MUST NOT reject any Precertificate that is overly redacted but "?.com" and "?.co.uk" would both be problematic). Logs MUST NOT
which is otherwise considered compliant. It is expected that reject any precertificate that is overly redacted but which is
monitors will treat overly redacted Precertificates as potentially otherwise considered compliant. It is expected that monitors will
misissued. TLS clients MAY reject a certificate whose corresponding treat overly redacted precertificates as potentially misissued. TLS
Precertificate would be overly redacted. clients MAY reject a certificate whose corresponding precertificate
would be overly redacted, perhaps using the same mechanism for
determining whether a wildcard in a domain name of a certificate is
too broad.
7.4. Misbehaving Logs 8.4. Misbehaving Logs
A log can misbehave in two ways: (1) by failing to incorporate a A log can misbehave in two ways: (1) by failing to incorporate a
certificate with an SCT in the Merkle Tree within the MMD and (2) by certificate with an SCT in the Merkle Tree within the MMD and (2) by
violating its append-only property by presenting two different, violating its append-only property by presenting two different,
conflicting views of the Merkle Tree at different times and/or to conflicting views of the Merkle Tree at different times and/or to
different parties. Both forms of violation will be promptly and different parties. Both forms of violation will be promptly and
publicly detectable. publicly detectable.
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 audit proof for each observed SCT. These checks can be Merkle audit proof for each observed SCT. These checks can be
skipping to change at page 28, line 20 skipping to change at page 32, line 18
Violation of the append-only property can be detected by clients Violation of the append-only property can be detected by clients
comparing their instances of the Signed Tree Heads. As soon as two comparing their instances of the Signed Tree Heads. As soon as two
conflicting Signed Tree Heads for the same log are detected, this is conflicting Signed Tree Heads for the same log are detected, this is
cryptographic proof of that log's misbehavior. There are various cryptographic proof of that log's misbehavior. There are various
ways this could be done, for example via gossip (see http:// ways this could be done, for example via gossip (see http://
trac.tools.ietf.org/id/draft-linus-trans-gossip-00.txt) or peer-to- trac.tools.ietf.org/id/draft-linus-trans-gossip-00.txt) or peer-to-
peer communications or by sending STHs to monitors (who could then peer communications or by sending STHs to monitors (who could then
directly check against their own copy of the relevant log). directly check against their own copy of the relevant log).
8. Efficiency Considerations 8.5. Multiple SCTs
TLS servers may wish to offer multiple SCTs, each from a different
log.
o If a CA and a log collude, it is possible to temporarily hide
misissuance from clients. Including SCTs from different logs
makes it more difficult to mount this attack.
o If a log misbehaves, a consequence may be that clients cease to
trust it. Since the time an SCT may be in use can be considerable
(several years is common in current practice when the SCT is
embedded in a certificate), servers may wish to reduce the
probability of their certificates being rejected as a result by
including SCTs from different logs.
o TLS clients may have policies related to the above risks requiring
servers to present multiple SCTs. For example Chromium
[Chromium.Log.Policy] currently requires multiple SCTs to be
presented with EV certificates in order for the EV indicator to be
shown.
9. Efficiency Considerations
The Merkle Tree design serves the purpose of keeping communication The Merkle Tree design serves the purpose of keeping communication
overhead low. overhead low.
Auditing logs for integrity does not require third parties to Auditing logs for integrity does not require third parties to
maintain a copy of each entire log. The Signed Tree Heads can be maintain a copy of each entire log. The Signed Tree Heads can be
updated as new entries become available, without recomputing entire updated as new entries become available, without recomputing entire
trees. Third-party auditors need only fetch the Merkle consistency trees. Third-party auditors need only fetch the Merkle consistency
proofs against a log's existing STH to efficiently verify the append- proofs against a log's existing STH to efficiently verify the append-
only property of updates to their Merkle Trees, without auditing the only property of updates to their Merkle Trees, without auditing the
entire tree. entire tree.
9. Acknowledgements 10. Acknowledgements
The authors would like to thank Erwann Abelea, Robin Alden, Al The authors would like to thank Erwann Abelea, Robin Alden, Al
Cutter, Francis Dupont, Stephen Farrell, Brad Hill, Jeff Hodges, Paul Cutter, Francis Dupont, Stephen Farrell, Brad Hill, Jeff Hodges, Paul
Hoffman, Jeffrey Hutzelman, SM, Alexey Melnikov, Chris Palmer, Trevor Hoffman, Jeffrey Hutzelman, SM, Alexey Melnikov, Chris Palmer, Trevor
Perrin, Ryan Sleevi and Carl Wallace for their valuable Perrin, Ryan Sleevi and Carl Wallace for their valuable
contributions. contributions.
10. References 11. References
10.1. Normative Reference
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
10.2. Informative References
[CrosbyWallach] 11.1. Normative References
Crosby, S. and D. Wallach, "Efficient Data Structures for
Tamper-Evident Logging", Proceedings of the 18th USENIX
Security Symposium, Montreal, August 2009,
<http://static.usenix.org/event/sec09/tech/full_papers/
crosby.pdf>.
[DSS] National Institute of Standards and Technology, "Digital [DSS] National Institute of Standards and Technology, "Digital
Signature Standard (DSS)", FIPS 186-3, June 2009, Signature Standard (DSS)", FIPS 186-3, June 2009,
<http://csrc.nist.gov/publications/fips/fips186-3/ <http://csrc.nist.gov/publications/fips/fips186-3/
fips_186-3.pdf>. fips_186-3.pdf>.
[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>.
[FIPS.180-4] [FIPS.180-4]
National Institute of Standards and Technology, "Secure National Institute of Standards and Technology, "Secure
Hash Standard", FIPS PUB 180-4, March 2012, Hash Standard", FIPS PUB 180-4, March 2012,
<http://csrc.nist.gov/publications/fips/fips180-4/ <http://csrc.nist.gov/publications/fips/fips180-4/
fips-180-4.pdf>. fips-180-4.pdf>.
[HTML401] Raggett, D., Le Hors, A., and I. Jacobs, "HTML 4.01 [HTML401] Raggett, D., Le Hors, A., and I. Jacobs, "HTML 4.01
Specification", World Wide Web Consortium Recommendation Specification", World Wide Web Consortium Recommendation
REC-html401-19991224, December 1999, REC-html401-19991224, December 1999,
<http://www.w3.org/TR/1999/REC-html401-19991224>. <http://www.w3.org/TR/1999/REC-html401-19991224>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2560] Myers, M., Ankney, R., Malpani, A., Galperin, S., and C. [RFC2560] Myers, M., Ankney, R., Malpani, A., Galperin, S., and C.
Adams, "X.509 Internet Public Key Infrastructure Online Adams, "X.509 Internet Public Key Infrastructure Online
Certificate Status Protocol - OCSP", RFC 2560, June 1999. Certificate Status Protocol - OCSP", RFC 2560, June 1999.
[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., [RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999. Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
[RFC3447] Jonsson, J. and B. Kaliski, "Public-Key Cryptography [RFC3447] Jonsson, J. and B. Kaliski, "Public-Key Cryptography
Standards (PKCS) #1: RSA Cryptography Specifications Standards (PKCS) #1: RSA Cryptography Specifications
skipping to change at page 30, line 29 skipping to change at page 34, line 29
[RFC6066] Eastlake, D., "Transport Layer Security (TLS) Extensions: [RFC6066] Eastlake, D., "Transport Layer Security (TLS) Extensions:
Extension Definitions", RFC 6066, January 2011. Extension Definitions", RFC 6066, January 2011.
[RFC6125] Saint-Andre, P. and J. Hodges, "Representation and [RFC6125] Saint-Andre, P. and J. Hodges, "Representation and
Verification of Domain-Based Application Service Identity Verification of Domain-Based Application Service Identity
within Internet Public Key Infrastructure Using X.509 within Internet Public Key Infrastructure Using X.509
(PKIX) Certificates in the Context of Transport Layer (PKIX) Certificates in the Context of Transport Layer
Security (TLS)", RFC 6125, March 2011. Security (TLS)", RFC 6125, March 2011.
11.2. Informative References
[Chromium.Log.Policy]
The Chromium Projects, "Chromium Certificate Transparency
Log Policy", 2014, <http://www.chromium.org/Home/
chromium-security/certificate-transparency/log-policy>.
[Chromium.Policy]
The Chromium Projects, "Chromium Certificate
Transparency", 2014, <http://www.chromium.org/Home/
chromium-security/certificate-transparency>.
[CrosbyWallach]
Crosby, S. and D. Wallach, "Efficient Data Structures for
Tamper-Evident Logging", Proceedings of the 18th USENIX
Security Symposium, Montreal, August 2009,
<http://static.usenix.org/event/sec09/tech/full_papers/
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>.
[JSON.Metadata]
The Chromium Projects, "Chromium Log Metadata JSON
Schema", 2014, <http://www.certificate-transparency.org/
known-logs/log_list_schema.json>.
[RFC6962] Laurie, B., Langley, A., and E. Kasper, "Certificate [RFC6962] Laurie, B., Langley, A., and E. Kasper, "Certificate
Transparency", RFC 6962, June 2013. Transparency", RFC 6962, June 2013.
Authors' Addresses Authors' Addresses
Ben Laurie Ben Laurie
Google UK Ltd. Google UK Ltd.
EMail: benl@google.com EMail: benl@google.com
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