draft-ietf-trans-rfc6962-bis-03.txt   draft-ietf-trans-rfc6962-bis-04.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: November 2, 2014 Google Expires: January 11, 2015 Google
R. Stradling R. Stradling
Comodo Comodo
May 1, 2014 July 10, 2014
Certificate Transparency Certificate Transparency
draft-ietf-trans-rfc6962-bis-03 draft-ietf-trans-rfc6962-bis-03
Abstract Abstract
This document describes an experimental protocol for publicly logging This document describes a protocol for publicly logging the existence
the existence of Transport Layer Security (TLS) certificates as they of Transport Layer Security (TLS) certificates as they are issued or
are issued or observed, in a manner that allows anyone to audit observed, in a manner that allows anyone to audit certificate
certificate authority (CA) activity and notice the issuance of authority (CA) activity and notice the issuance of suspect
suspect certificates as well as to audit the certificate logs certificates as well as to audit the certificate logs themselves.
themselves. The intent is that eventually clients would refuse to The intent is that eventually clients would refuse to honor
honor certificates that do not appear in a log, effectively forcing certificates that do not appear in a log, effectively forcing CAs to
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
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on November 2, 2014. This Internet-Draft will expire on January 11, 2015.
Copyright Notice Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the Copyright (c) 2014 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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2.1.1. Merkle Audit Paths . . . . . . . . . . . . . . . . . 5 2.1.1. Merkle Audit Paths . . . . . . . . . . . . . . . . . 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 . . . . . . . . . . . . . . . . . . . . . 8
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 . . . . . . 13 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 . . . . . . . . . . . . . . . . . . . . 17 3.4.1. TLS Extension . . . . . . . . . . . . . . . . . . . . 17
3.5. Merkle Tree . . . . . . . . . . . . . . . . . . . . . . . 17 3.5. Merkle Tree . . . . . . . . . . . . . . . . . . . . . . . 17
3.6. Signed Tree Head . . . . . . . . . . . . . . . . . . . . 18 3.6. Signed Tree Head . . . . . . . . . . . . . . . . . . . . 18
4. Log Client Messages . . . . . . . . . . . . . . . . . . . . . 19 4. Log Client Messages . . . . . . . . . . . . . . . . . . . . . 19
4.1. Add Chain to Log . . . . . . . . . . . . . . . . . . . . 19 4.1. Add Chain to Log . . . . . . . . . . . . . . . . . . . . 20
4.2. Add PreCertChain to Log . . . . . . . . . . . . . . . . . 20 4.2. Add PreCertChain to Log . . . . . . . . . . . . . . . . . 21
4.3. Retrieve Latest Signed Tree Head . . . . . . . . . . . . 20 4.3. Retrieve Latest Signed Tree Head . . . . . . . . . . . . 21
4.4. Retrieve Merkle Consistency Proof between Two Signed Tree 4.4. Retrieve Merkle Consistency Proof between Two Signed Tree
Heads . . . . . . . . . . . . . . . . . . . . . . . . . . 21 Heads . . . . . . . . . . . . . . . . . . . . . . . . . . 21
4.5. Retrieve Merkle Audit Proof from Log by Leaf Hash . . . . 21 4.5. Retrieve Merkle Audit Proof from Log by Leaf Hash . . . . 22
4.6. Retrieve Entries from Log . . . . . . . . . . . . . . . . 22 4.6. Retrieve Entries from Log . . . . . . . . . . . . . . . . 22
4.7. Retrieve Accepted Root Certificates . . . . . . . . . . . 23 4.7. Retrieve Accepted Root Certificates . . . . . . . . . . . 23
4.8. Retrieve Entry+Merkle Audit Proof from Log . . . . . . . 23 4.8. Retrieve Entry+Merkle Audit Proof from Log . . . . . . . 24
5. Clients . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 5. Clients . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
5.1. Submitters . . . . . . . . . . . . . . . . . . . . . . . 24 5.1. Submitters . . . . . . . . . . . . . . . . . . . . . . . 24
5.2. TLS Client . . . . . . . . . . . . . . . . . . . . . . . 24 5.2. TLS Client . . . . . . . . . . . . . . . . . . . . . . . 25
5.3. Monitor . . . . . . . . . . . . . . . . . . . . . . . . . 24 5.3. Monitor . . . . . . . . . . . . . . . . . . . . . . . . . 25
5.4. Auditor . . . . . . . . . . . . . . . . . . . . . . . . . 25 5.4. Auditor . . . . . . . . . . . . . . . . . . . . . . . . . 26
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 26 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 26
7. Security Considerations . . . . . . . . . . . . . . . . . . . 26 6.1. TLS Extension Type . . . . . . . . . . . . . . . . . . . 26
7.1. Misissued Certificates . . . . . . . . . . . . . . . . . 26 6.2. Hash Algorithms . . . . . . . . . . . . . . . . . . . . . 26
7.2. Detection of Misissue . . . . . . . . . . . . . . . . . . 26 7. Security Considerations . . . . . . . . . . . . . . . . . . . 27
7.3. Redaction of Public Domain Name Labels . . . . . . . . . 26 7.1. Misissued Certificates . . . . . . . . . . . . . . . . . 27
7.4. Misbehaving Logs . . . . . . . . . . . . . . . . . . . . 27 7.2. Detection of Misissue . . . . . . . . . . . . . . . . . . 27
8. Efficiency Considerations . . . . . . . . . . . . . . . . . . 27 7.3. Redaction of Public Domain Name Labels . . . . . . . . . 27
9. Future Changes . . . . . . . . . . . . . . . . . . . . . . . 27 7.4. Misbehaving Logs . . . . . . . . . . . . . . . . . . . . 28
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 28 8. Efficiency Considerations . . . . . . . . . . . . . . . . . . 28
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 28 9. Future Changes . . . . . . . . . . . . . . . . . . . . . . . 28
11.1. Normative Reference . . . . . . . . . . . . . . . . . . 28 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 29
11.2. Informative References . . . . . . . . . . . . . . . . . 28 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 29
11.1. Normative Reference . . . . . . . . . . . . . . . . . . 29
11.2. Informative References . . . . . . . . . . . . . . . . . 29
1. Informal Introduction 1. Informal 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 certificate 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; it is also expected newly issued certificates to one or more logs, however certificate
that certificate holders will contribute their own certificate holders can also contribute their own certificate chains, as can
chains. In order to avoid logs being spammed into uselessness, it is third parties. In order to avoid logs being rendered useless by
required that each chain is rooted in a known CA certificate. When a submitting large numbers of spurious certificates, it is required
chain is submitted to a log, a signed timestamp is returned, which that each chain is rooted in a CA certificate accepted by the log.
can later be used to provide evidence to clients that the chain has When a chain is submitted to a log, a signed timestamp is returned,
been submitted. TLS clients can thus require that all certificates which can later be used to provide evidence to TLS clients that the
they see have been logged. chain has been submitted. TLS clients can thus require that all
certificates they accept as valid have been logged.
Those who are concerned about misissue can monitor the logs, asking Those who are concerned about misissue can monitor the logs, asking
them regularly for all new entries, and can thus check whether them regularly for all new entries, and can thus check whether
domains they are responsible for have had certificates issued that domains they are responsible for have had certificates issued that
they did not expect. What they do with this information, they did not expect. What they do with this information,
particularly when they find that a misissuance has happened, is particularly when they find that a misissuance has happened, is
beyond the scope of this document, but broadly speaking, they can beyond the scope of this document, but broadly speaking, they can
invoke existing business mechanisms for dealing with misissued invoke existing business mechanisms for dealing with misissued
certificates. Of course, anyone who wants can monitor the logs and, certificates, such as working with the CA to get the certificate
if they believe a certificate is incorrectly issued, take action as revoked, or with maintainers of trust anchor lists to get the CA
they see fit. removed. Of course, anyone who wants can monitor the logs and, if
they believe a certificate is incorrectly issued, take action as they
see fit.
Similarly, those who have seen signed timestamps from a particular Similarly, those who have seen signed timestamps from a particular
log can later demand a proof of inclusion from that log. If the log log can later demand a proof of inclusion from that log. If the log
is unable to provide this (or, indeed, if the corresponding is unable to provide this (or, indeed, if the corresponding
certificate is absent from monitors' copies of that log), that is certificate is absent from monitors' copies of that log), that is
evidence of the incorrect operation of the log. The checking evidence of the incorrect operation of the log. The checking
operation is asynchronous to allow TLS connections to proceed without operation is asynchronous to allow TLS connections to proceed without
delay, despite network connectivity issues and the vagaries of delay, despite network connectivity issues and the vagaries of
firewalls. firewalls.
The append-only property of each log is technically achieved using The append-only property of each log is technically achieved using
Merkle Trees, which can be used to show that any particular version Merkle Trees, which can be used to show that any particular instance
of the log is a superset of any particular previous version. of the log is a superset of any particular previous instance.
Likewise, Merkle Trees avoid the need to blindly trust logs: if a log Likewise, Merkle Trees avoid the need to blindly trust logs: if a log
attempts to show different things to different people, this can be attempts to show different things to different people, this can be
efficiently detected by comparing tree roots and consistency proofs. efficiently detected by comparing tree roots and consistency proofs.
Similarly, other misbehaviors of any log (e.g., issuing signed Similarly, other misbehaviors of any log (e.g., issuing signed
timestamps for certificates they then don't log) can be efficiently timestamps for certificates they then don't log) can be efficiently
detected and proved to the world at large. detected and proved to the world at large.
1.1. Requirements Language 1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
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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 is SHA-256 [FIPS.180-4] (note that this is fixed hashing algorithm used by each log is expected to be specified as
for this experiment, but it is anticipated that each log would be part of the metadata relating to that log. We have established a
able to specify a hash algorithm). The input to the Merkle Tree Hash registry of acceptable algorithms, see Section 6.2. The hashing
is a list of data entries; these entries will be hashed to form the algorithm in use is referred to as HASH throughout this document.
leaves of the Merkle Hash Tree. The output is a single 32-byte The input to the Merkle Tree Hash is a list of data entries; these
Merkle Tree Hash. Given an ordered list of n inputs, D[n] = {d(0), entries will be hashed to form the leaves of the Merkle Hash Tree.
d(1), ..., d(n-1)}, the Merkle Tree Hash (MTH) is thus defined as The output is a single 32-byte Merkle Tree Hash. Given an ordered
follows: list of n inputs, D[n] = {d(0), d(1), ..., d(n-1)}, the Merkle Tree
Hash (MTH) is thus defined as follows:
The hash of an empty list is the hash of an empty string: The hash of an empty list is the hash of an empty string:
MTH({}) = SHA-256(). MTH({}) = HASH().
The hash of a list with one entry (also known as a leaf hash) is: The hash of a list with one entry (also known as a leaf hash) is:
MTH({d(0)}) = SHA-256(0x00 || d(0)). MTH({d(0)}) = HASH(0x00 || d(0)).
For n > 1, let k be the largest power of two smaller than n (i.e., k For n > 1, let k be the largest power of two smaller than n (i.e., k
< n <= 2k). The Merkle Tree Hash of an n-element list D[n] is then < n <= 2k). The Merkle Tree Hash of an n-element list D[n] is then
defined recursively as defined recursively as
MTH(D[n]) = SHA-256(0x01 || MTH(D[0:k]) || MTH(D[k:n])), MTH(D[n]) = HASH(0x01 || MTH(D[0:k]) || MTH(D[k:n])),
where || is concatenation and D[k1:k2] denotes the list {d(k1), where || is concatenation and D[k1:k2] denotes the list {d(k1),
d(k1+1),..., d(k2-1)} of length (k2 - k1). (Note that the hash d(k1+1),..., d(k2-1)} of length (k2 - k1). (Note that the hash
calculations for leaves and nodes differ. This domain separation is calculations for leaves and nodes differ. This domain separation is
required to give second preimage resistance.) required to give second preimage resistance.)
Note that we do not require the length of the input list to be a Note that we do not require the length of the input list to be a
power of two. The resulting Merkle Tree may thus not be balanced; power of two. The resulting Merkle Tree may thus not be balanced;
however, its shape is uniquely determined by the number of leaves. however, its shape is uniquely determined by the number of leaves.
(Note: This Merkle Tree is essentially the same as the history tree (Note: This Merkle Tree is essentially the same as the history tree
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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 When a valid certificate is submitted to a log, the log MUST return a
immediately return a Signed Certificate Timestamp (SCT). The SCT is Signed Certificate Timestamp (SCT). The SCT is the log's promise to
the log's promise to incorporate the certificate in the Merkle Tree incorporate the certificate in the Merkle Tree within a fixed amount
within a fixed amount of time known as the Maximum Merge Delay (MMD). of time known as the Maximum Merge Delay (MMD). If the log has
If the log has previously seen the certificate, it MAY return the previously seen the certificate, it MAY return the same SCT as it
same SCT as it returned before. TLS servers MUST present an SCT from returned before. TLS servers MUST present an SCT from one or more
one or more logs to the TLS client together with the certificate. logs to the TLS client together with the certificate. TLS clients
TLS clients MUST reject certificates that do not have a valid SCT for MUST reject certificates that are not accompanied by an SCT for
the end-entity certificate. either the end-entity certificate or for a name-constrained
intermediate the end-entity certificate chains to.
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.
3.1. Log Entries 3.1. Log Entries
Anyone can submit a certificate to any log. In order to enable In order to enable attribution of each logged certificate to its
attribution of each logged certificate to its issuer, the log SHALL issuer, each submitted certificate MUST be accompanied by all
publish a list of acceptable root certificates (this list might
usefully be the union of root certificates trusted by major browser
vendors). 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. omitted from the chain submitted to the log server. The log SHALL
allow retrieval of a list of acceptable root certificates (this list
might usefully be the union of root certificates trusted by major
browser vendors).
Alternatively, (root as well as intermediate) certificate authorities Alternatively, (root as well as intermediate) certificate authorities
may submit a certificate to logs prior to issuance in order to may submit a certificate to logs prior to issuance in order to
incorporate the SCT in the issued certificate. To do so, the CA incorporate the SCT in the issued certificate. To do so, the CA
submits a Precertificate that the log can use to create an entry that submits a Precertificate that the log can use to create an entry that
will be valid against the issued certificate. The Precertificate is will be valid against the issued certificate. The Precertificate is
an X.509v3 certificate for simplicity, but, since it isn't used for an X.509v3 certificate for simplicity, but, since it isn't used for
anything but logging, could equally be some other data structure. anything but logging, could equally be some other data structure.
The Precertificate is constructed from the certificate to be issued The Precertificate is constructed from the certificate to be issued
by adding a special critical poison extension (OID by adding a special critical poison extension (OID
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accommodate quirks of CA certificate-issuing software. However, logs accommodate quirks of CA certificate-issuing software. However, logs
MUST refuse to publish certificates without a valid chain to a known MUST refuse to publish certificates without a valid chain to a known
root CA. If a certificate is accepted and an SCT issued, the root CA. 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 control spam for those certificates is found. The authors welcome to limit the submission of spurious certificates is found. The
suggestions.) authors welcome suggestions.)
Each certificate entry in a log MUST include the following Each certificate entry in a log MUST include the following
components: components:
enum { x509_entry(0), precert_entry(1), (65535) } LogEntryType; enum { x509_entry(0), precert_entry(1), (65535) } LogEntryType;
struct { struct {
LogEntryType entry_type; LogEntryType entry_type;
select (entry_type) { select (entry_type) {
case x509_entry: X509ChainEntry; case x509_entry: X509ChainEntry;
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struct { struct {
ASN.1Cert leaf_certificate; ASN.1Cert leaf_certificate;
ASN.1Cert certificate_chain<0..2^24-1>; ASN.1Cert certificate_chain<0..2^24-1>;
} X509ChainEntry; } X509ChainEntry;
struct { struct {
ASN.1Cert pre_certificate; ASN.1Cert pre_certificate;
ASN.1Cert precertificate_chain<0..2^24-1>; ASN.1Cert precertificate_chain<0..2^24-1>;
} PrecertChainEntry; } PrecertChainEntry;
Logs MAY limit the length of chain they will accept. Logs SHOULD limit the length of chain they will accept.
"entry_type" is the type of this entry. Future revisions of this "entry_type" is the type of this entry. Future revisions of this
protocol version may add new LogEntryType values. Section 4 explains protocol may add new LogEntryType values. Section 4 explains how
how clients should handle unknown entry types. clients should handle unknown entry types.
"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 be directly certify the one preceding it. The final certificate MUST
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 MAY to verify the Precertificate submission. The first certificate MAY
be a valid Precertificate Signing Certificate and MUST certify the be a valid Precertificate Signing Certificate and MUST certify the
first certificate. Each following certificate MUST directly certify first certificate. Each following certificate MUST directly certify
the one preceding it. The final certificate MUST be a root 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
Enterprises regard some DNS domain name labels within their Some regard some DNS domain name labels within their registered
registered domain space as private and security sensitive. Even domain space as private and security sensitive. Even though these
though these domains are often only accessible within the domains are often only accessible within the domain owner's private
enterprise's private network, it's common for them to be secured network, it's common for them to be secured using publicly trusted
using publicly trusted TLS server certificates. Enterprises don't TLS server certificates. We define a mechanism to allow these
want these private labels to appear in public logs. private labels to not appear in public logs.
3.2.1. Wildcard Certificates 3.2.1. Wildcard Certificates
A certificate containing a DNS-ID [RFC6125] of "*.example.com" could A certificate containing a DNS-ID [RFC6125] of "*.example.com" could
be used to secure the domain "topsecret.example.com", without be used to secure the domain "topsecret.example.com", without
revealing the string "topsecret" publicly. revealing the string "topsecret" publicly.
Since TLS clients only match the wildcard character to the complete Since TLS clients only match the wildcard character to the complete
leftmost label of the DNS domain name (see Section 6.4.3 of leftmost label of the DNS domain name (see Section 6.4.3 of
[RFC6125]), this approach would not work for a DNS-ID such as [RFC6125]), this approach would not work for a DNS-ID such as
skipping to change at page 12, line 39 skipping to change at page 12, line 39
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 of
the complete leftmost labels in each DNS-ID with the literal string the complete leftmost labels in each DNS-ID with the literal string
"(PRIVATE)". For example, if a certificate contains a DNS-ID of "(PRIVATE)". For example, if a certificate contains a DNS-ID of
"top.secret.example.com", then the corresponding Precertificate could "top.secret.example.com", then the corresponding Precertificate could
contain "(PRIVATE).example.com" instead. Labels in a CN-ID [RFC6125] contain "(PRIVATE).example.com" instead. Labels in a CN-ID [RFC6125]
MUST remain unredacted. MUST remain unredacted.
When a Precertificate contains one or more redacted labels, an When a Precertificate contains one or more redacted labels, a non-
extension (OID 1.3.6.1.4.1.11129.2.4.6, whose extnValue OCTET STRING critical extension (OID 1.3.6.1.4.1.11129.2.4.6, whose extnValue
contains an ASN.1 SEQUENCE OF INTEGERs) MUST be added to the OCTET STRING contains an ASN.1 SEQUENCE OF INTEGERs) MUST be added to
corresponding certificate: the first INTEGER indicates the number of the corresponding certificate: the first INTEGER indicates the number
labels redacted in the Precertificate's first DNS-ID; the second of labels redacted in the Precertificate's first DNS-ID; the second
INTEGER does the same for the Precertificate's second DNS-ID; etc. INTEGER does the same for the Precertificate's second DNS-ID; etc.
There MUST NOT be more INTEGERs than there are DNS-IDs. If there are There MUST NOT be more INTEGERs than there are DNS-IDs. If there are
fewer INTEGERs than there are DNS-IDs, the shortfall is made up by fewer INTEGERs than there are DNS-IDs, the shortfall is made up by
implicitly repeating the last INTEGER. Each INTEGER MUST have a implicitly repeating the last INTEGER. Each INTEGER MUST have a
value of zero or more. The purpose of this extension is to enable value of zero or more. The purpose of this extension is to enable
TLS clients to accurately reconstruct the Precertificate from the TLS clients to accurately reconstruct the Precertificate from the
certificate without having to perform any guesswork. certificate without having to perform any guesswork.
3.2.3. Using a Name-Constrained Intermediate CA 3.2.3. Using a Name-Constrained Intermediate CA
An intermediate CA certificate or Precertificate that contains the An intermediate CA certificate or Precertificate that contains the
Name Constraints extension (see Section 4.2.1.10 of [RFC5280]) MAY be critical or non-critical Name Constraints [RFC5280] extension MAY be
logged in place of end-entity certificates issued by that logged in place of end-entity certificates issued by that
intermediate CA, as long as all of the following conditions are met: intermediate CA, as long as all of the following conditions are met:
o there MUST be an extension (OID 1.3.6.1.4.1.11129.2.4.7, whose o there MUST be a non-critical extension (OID
extnValue OCTET STRING contains ASN.1 NULL data (0x05 0x00)). 1.3.6.1.4.1.11129.2.4.7, whose extnValue OCTET STRING contains
This extension is an explicit indication that it is acceptable to ASN.1 NULL data (0x05 0x00)). This extension is an explicit
not log certificates issued by this intermediate CA. indication that it is acceptable to not log certificates issued by
this intermediate CA.
o permittedSubtrees MUST specify one or more dNSNames. o permittedSubtrees MUST specify one or more dNSNames.
o excludedSubtrees MUST specify the entire IPv4 and IPv6 address o excludedSubtrees MUST specify the entire IPv4 and IPv6 address
ranges. ranges.
Below is an example Name Constraints extension that meets these Below is an example Name Constraints extension that meets these
conditions: conditions:
SEQUENCE { SEQUENCE {
skipping to change at page 15, line 44 skipping to change at page 15, line 44
"signed_entry" is the "leaf_certificate" (in the case of an "signed_entry" is the "leaf_certificate" (in the case of an
X509ChainEntry) or is the PreCert (in the case of a X509ChainEntry) or is the PreCert (in the case of a
PrecertChainEntry), as described above. PrecertChainEntry), as described above.
"extensions" are future extensions to this protocol version (v1). "extensions" are future extensions to this protocol version (v1).
Currently, no extensions are specified. Currently, no extensions are specified.
3.4. Including the Signed Certificate Timestamp in the TLS Handshake 3.4. Including the Signed Certificate Timestamp in the TLS Handshake
The SCT data corresponding to the end-entity certificate from at The SCT data corresponding to at least one certificate in the chain
least one log must be included in the TLS handshake, either by using from at least one log must be included in the TLS handshake, either
an X509v3 certificate extension as described below, by using a TLS by using an X509v3 certificate extension as described below, by using
extension (Section 7.4.1.4 of [RFC5246]) with type a TLS extension (Section 7.4.1.4 of [RFC5246]) with type
"signed_certificate_timestamp", or by using Online Certificate Status "signed_certificate_timestamp", or by using Online Certificate Status
Protocol (OCSP) Stapling (also known as the "Certificate Status Protocol (OCSP) Stapling (also known as the "Certificate Status
Request" TLS extension; see [RFC6066]), where the OCSP response Request" TLS extension; see [RFC6066]), where the OCSP response
includes an extension with OID 1.3.6.1.4.1.11129.2.4.5 (see includes a non-critical extension with OID 1.3.6.1.4.1.11129.2.4.5
[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 certificate 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 final certificate, by encoding the SignedCertificateTimestampList the final certificate, by encoding the SignedCertificateTimestampList
structure as an ASN.1 OCTET STRING and inserting the resulting data structure as an ASN.1 OCTET STRING and inserting the resulting data
in the TBSCertificate as an X.509v3 certificate extension (OID in the TBSCertificate as a non-critical X.509v3 certificate extension
1.3.6.1.4.1.11129.2.4.2). Upon receiving the certificate, clients (OID 1.3.6.1.4.1.11129.2.4.2). Upon receiving the certificate,
can reconstruct the original TBSCertificate to verify the SCT clients can reconstruct the original TBSCertificate to verify the SCT
signature. 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:
opaque SerializedSCT<1..2^16-1>; opaque SerializedSCT<1..2^16-1>;
struct { struct {
SerializedSCT sct_list <1..2^16-1>; SerializedSCT sct_list <1..2^16-1>;
} SignedCertificateTimestampList; } SignedCertificateTimestampList;
Here, "SerializedSCT" is an opaque byte string that contains the Here, "SerializedSCT" is an opaque byte string that contains the
serialized TLS structure. This encoding ensures that TLS clients can serialized SCT structure. This encoding ensures that TLS clients can
decode each SCT individually (i.e., if there is a version upgrade, decode each SCT individually (i.e., if there is a version upgrade,
out-of-date clients can still parse old SCTs while skipping over new out-of-date clients can still parse old SCTs while skipping over new
SCTs whose versions they don't understand). SCTs whose versions they don't understand).
Likewise, SCTs can be embedded in a TLS extension. See below for Likewise, SCTs can be embedded in a TLS extension. See below for
details. details.
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 or has had a key compromise). struck off for misbehavior, has had a key compromise or is not known
to the client).
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 to clients who have indicated support for
the extension in the ClientHello, in which case the SCTs are sent by the extension in the ClientHello, in which case the SCTs are sent by
setting the "extension_data" to a "SignedCertificateTimestampList". 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 SHA-256. The hashing algorithm for the Merkle Tree Hash is specified in the
log's metadata.
Structure of the Merkle Tree input: Structure of the Merkle Tree input:
enum { timestamped_entry(0), (255) } enum { v1(0), v2(1), (255) }
MerkleLeafType; 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: PreCert; case precert_entry: PreCert;
} signed_entry; } signed_entry;
CtExtensions extensions; CtExtensions extensions;
} TimestampedEntry; } TimestampedEntry;
struct { struct {
Version version; LeafVersion version;
MerkleLeafType leaf_type; TimestampedEntry timestamped_entry;
select (leaf_type) {
case timestamped_entry: TimestampedEntry;
}
} MerkleTreeLeaf; } MerkleTreeLeaf;
Here, "version" is the version of the protocol to which the Here, "version" is the version of the MerkleTreeLeaf structure. This
MerkleTreeLeaf corresponds. This version is v1. version is v2. Note that MerkleTreeLeaf v1 [RFC6962] had another
layer of indirection which is removed in v2.
"leaf_type" is the type of the leaf input. Currently, only
"timestamped_entry" (corresponding to an SCT) is defined. Future
revisions of this protocol version may add new MerkleLeafType types.
Section 4 explains how clients should handle unknown leaf types.
"timestamp" is the timestamp of the corresponding SCT issued for this "timestamp" is the timestamp of the corresponding SCT issued for this
certificate. certificate.
"entry_type" is the type of entry stored in "signed_entry". New
"LogEntryType" values may be added to "signed_entry" without
increasing the "MerkleTreeLeaf" version. Section 4 explains how
clients should handle unknown entry types.
"signed_entry" is the "signed_entry" of the corresponding SCT. "signed_entry" is the "signed_entry" of the corresponding SCT.
"extensions" are "extensions" of the corresponding SCT. "extensions" are "extensions" of the corresponding SCT.
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), v2(1), (255) }
TreeHeadVersion;
digitally-signed struct { digitally-signed struct {
Version 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 protocol to which the "version" is the version of the TreeHeadSignature structure. This
TreeHeadSignature conforms. This version is v1. version is v2.
"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-
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
specified here. These extra fields should be ignored. specified here. These extra fields should be ignored.
The <log server> prefix can 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.
Any errors will be returned as HTTP 4xx or 5xx responses, with human- If the log is unable to process a client's request, it MUST return an
readable error messages. HTTP response code of 4xx/5xx (see [RFC2616]), and, in place of the
responses outlined in the subsections below, the body SHOULD be a
JSON structure containing at least the following field:
error_message:
A human-readable string describing the error which prevented
the log from processing the request.
In the case of a malformed request, the string SHOULD provide
sufficient detail for the error to be rectified.
e.g. In response to a request of "/ct/v1/get-
entries?start=100&end=99", the log would return a "400 Bad Request"
response code with a body similar to the following:
{
"error_message": "'start' cannot be greater than 'end'",
}
Clients SHOULD treat "500 Internal Server Error" and "503 Service
Unavailable" responses as transient failures and MAY retry the same
request without modification at a later date. Note that as per
[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
client to wait before retrying the request.
4.1. Add Chain to Log 4.1. Add Chain to Log
POST https://<log server>/ct/v1/add-chain POST https://<log server>/ct/v1/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 end-entity certificate; the second chains to the element is the end-entity certificate; the second chains to the
first and so on to the last, which is either the root first and so on to the last, which is either the root
certificate or a certificate that chains to a known root certificate or a certificate that chains to a known root
certificate. certificate.
Outputs: Outputs:
sct_version: The version of the SignedCertificateTimestamp sct_version: The version of the SignedCertificateTimestamp
structure, in decimal. A compliant v1 implementation MUST NOT structure, in decimal. A compliant v1 implementation MUST NOT
expect this to be 0 (i.e., v1). expect this to be 0 (i.e., v1).
id: The log ID, base64 encoded. Since log clients who request an id: The log ID, base64 encoded.
SCT for inclusion in TLS handshakes are not required to verify
it, we do not assume they know the ID of the log.
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.
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. (Note: verify the signature. It MUST NOT construe this as an error. This
Log clients don't need to be able to verify this structure; only TLS is to avoid forcing an upgrade of compliant v1 clients that do not
clients do. If we were to serve the structure as a binary blob, then use the returned SCTs.
we could completely change it without requiring an upgrade to v1
clients.)
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:
chain: An array of base64-encoded Precertificates. The first chain: An array of base64-encoded Precertificates. The first
element is the end-entity certificate; the second chains to the element is the end-entity certificate; the second chains to the
first and so on to the last, which is either the root first and so on to the last, which is either the root
skipping to change at page 21, line 13 skipping to change at page 21, line 41
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/v1/get-sth-consistency
Inputs: Inputs:
first: The tree_size of the first tree, in decimal. first: The tree_size of the older tree, in decimal.
second: The tree_size of the second tree, in decimal. second: The tree_size of the newer tree, in decimal.
Both tree sizes must be from existing v1 STHs (Signed Tree Heads). Both tree sizes must be from existing v1 STHs (Signed Tree Heads).
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 Note that no signature is required on this data, as it is used to
verify an STH, which is signed. verify an STH, which is signed.
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leaf_input: The base64-encoded MerkleTreeLeaf structure. leaf_input: The base64-encoded MerkleTreeLeaf structure.
extra_data: The base64-encoded unsigned data pertaining to the extra_data: The base64-encoded unsigned data pertaining to the
log entry. In the case of an X509ChainEntry, this is the log entry. In the case of an X509ChainEntry, this is the
"certificate_chain". In the case of a PrecertChainEntry, "certificate_chain". In the case of a PrecertChainEntry,
this is the whole "PrecertChainEntry". this is the whole "PrecertChainEntry".
Note that this message is not signed -- the retrieved data can be Note that this message is not signed -- the retrieved 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 v1. However, a compliant v1 retrieved STH. All leaves MUST be v1 or v2. However, a compliant v1
client MUST NOT construe an unrecognized MerkleLeafType or client MUST NOT construe an unrecognized LogEntryType value as an
LogEntryType value as an error. This means it may be unable to parse error. This means it may be unable to parse some entries, but note
some entries, but note that each client can inspect the entries it that each client can inspect the entries it does recognize as well as
does recognize as well as verify the integrity of the data by verify the integrity of the data by treating unrecognized leaves as
treating unrecognized leaves as opaque input to the tree. opaque 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 4.3. "tree_size" as returned by "get-sth" in Section 4.3.
Logs MAY honor requests where 0 <= "start" < "tree_size" and "end" >= Logs MAY honor requests where 0 <= "start" < "tree_size" and "end" >=
"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
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from denying that misbehavior. from denying that misbehavior.
All clients should gossip with each other, exchanging STHs at least; All clients should gossip with each other, exchanging STHs at least;
this is all that is required to ensure that they all have a this is all that is required to ensure that they all have a
consistent view. The exact mechanism for gossip will be described in consistent view. The exact mechanism for gossip will be described in
a separate document, but it is expected there will be a variety. a separate document, but it is expected there will be a variety.
5.1. Submitters 5.1. Submitters
Submitters submit certificates or Precertificates to the log as Submitters submit certificates or Precertificates to the log as
described above. They may go on to use the returned SCT to construct described above. When a Submitter intends to use the returned SCT
a certificate or use it directly in a TLS handshake. directly in a TLS handshake or to construct a certificate, they
SHOULD validate the SCT as described in Section 5.2 if they
understand its format.
5.2. TLS Client 5.2. TLS Client
TLS clients are not directly clients of the log, but they receive TLS clients receive SCTs alongside or in server certificates. In
SCTs alongside or in server certificates. In addition to normal addition to normal validation of the certificate and its chain, TLS
validation of the certificate and its chain, they should validate the clients SHOULD validate the SCT by computing the signature input from
SCT by computing the signature input from the SCT data as well as the the SCT data as well as the certificate and verifying the signature,
certificate and verifying the signature, using the corresponding using the corresponding log's public key. TLS clients MAY audit the
log's public key. Note that this document does not describe how corresponding log by requesting, and verifying, a Merkle audit proof
clients obtain the logs' public keys. for said certificate. Note that this document does not describe how
clients obtain the logs' public keys or URLs.
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 5.3. Monitor
Monitors watch logs and check that they behave correctly. They also Monitors watch logs and check that they behave correctly. They also
watch for certificates of interest. watch for certificates of interest.
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
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A certificate accompanied by an SCT can be verified against any STH A certificate accompanied by an SCT can be verified against any STH
dated after the SCT timestamp + the Maximum Merge Delay by requesting dated after the SCT timestamp + the Maximum Merge Delay by requesting
a Merkle audit proof (Section 4.5). a Merkle audit proof (Section 4.5).
Auditors can fetch STHs from time to time of their own accord, of Auditors can fetch STHs from time to time of their own accord, of
course (Section 4.3). course (Section 4.3).
6. IANA Considerations 6. IANA Considerations
6.1. 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.
6.2. Hash Algorithms
IANA is asked to establish a registry of hash values, initially
consisting of:
+-------+----------------------+
| Index | Hash |
+-------+----------------------+
| 0 | SHA-256 [FIPS.180-4] |
+-------+----------------------+
7. Security Considerations 7. 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 the certificate has been published in a log. From this, knows that a log has committed to publishing the certificate. From
the client knows that the subject of the certificate has had some this, the client knows that the subject of the certificate has had
time to notice the misissue and take some action, such as asking a CA some time to notice the misissue and take some action, such as asking
to revoke a misissued certificate. A signed timestamp is not a a CA to revoke a misissued certificate, or that the log has
guarantee that the certificate is not misissued, since the subject of misbehaved, which will be discovered when the SCT is audited. A
the certificate might not have checked the logs or the CA might have signed timestamp is not a guarantee that the certificate is not
refused to revoke the certificate. misissued, since the subject of the certificate might not have
checked 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.
7.1. Misissued Certificates 7.1. 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
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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
asynchronous and need only be done once per each certificate. In asynchronous and need only be done once per each certificate. In
order to protect the clients' privacy, these checks need not reveal order to protect the clients' privacy, these checks need not reveal
the exact certificate to the log. Clients can instead request the the exact certificate to the log. Clients can instead request the
proof from a trusted auditor (since anyone can compute the audit proof from a trusted auditor (since anyone can compute the audit
proofs from the log) or request Merkle proofs for a batch of proofs from the log) or request Merkle proofs for a batch of
certificates around the SCT timestamp. certificates around the SCT timestamp.
Violation of the append-only property is detected by global Violation of the append-only property is detected by global
gossiping, i.e., everyone auditing logs comparing their versions of gossiping, i.e., everyone auditing logs comparing their instances of
the latest Signed Tree Heads. As soon as two conflicting Signed Tree the latest Signed Tree Heads. As soon as two conflicting Signed Tree
Heads for the same log are detected, this is cryptographic proof of Heads for the same log are detected, this is cryptographic proof of
that log's misbehavior. that log's misbehavior.
8. Efficiency Considerations 8. 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
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[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>.
[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.,
Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
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
Version 2.1", RFC 3447, February 2003. Version 2.1", RFC 3447, February 2003.
[RFC4627] Crockford, D., "The application/json Media Type for [RFC4627] Crockford, D., "The application/json Media Type for
JavaScript Object Notation (JSON)", RFC 4627, July 2006. JavaScript Object Notation (JSON)", RFC 4627, July 2006.
[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data [RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, October 2006. Encodings", RFC 4648, October 2006.
skipping to change at page 29, line 45 skipping to change at page 30, line 49
[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.
[RFC6962] Laurie, B., Langley, A., and E. Kasper, "Certificate
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
Adam Langley Adam Langley
Google Inc. Google Inc.
EMail: agl@google.com EMail: agl@google.com
Emilia Kasper Emilia Kasper
Google Switzerland GmbH Google Switzerland GmbH
EMail: ekasper@google.com EMail: ekasper@google.com
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