Internet DRAFT - draft-kent-trans-architecture
draft-kent-trans-architecture
Public Notary Transparency S. Kent
Internet Draft D. Mandelberg
Intended status: Standards Track K. Seo
Expires: June 2018 December 12, 2017
Certificate Transparency (CT) System Architecture
draft-kent-trans-architecture-07.txt
Abstract
This document describes the architecture for Certificate Transparency
(CT) focusing on the Web PKI context. It defines the goals of CT and
the elements that comprise the CT system. It also describes the major
features of these elements. Other documents, cited in the References,
establish requirements for these CT system elements and describe
their operation in greater detail.
Status of this Memo
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Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction...................................................2
1.1. Requirements Language.....................................5
2. Beneficiaries of CT............................................6
3. The Elements of the CT Architecture............................7
3.1. Logs.....................................................10
3.2. CT-aware Certification Authorities (CAs).................11
3.3. Monitors.................................................12
3.4. CT-aware Subjects (TLS web servers)......................13
3.5. CT-aware TLS clients (web browsers)......................14
3.6. Auditors.................................................15
4. Security Considerations.......................................15
5. IANA Considerations...........................................16
6. References....................................................16
6.1. Normative References.....................................16
6.2. Informative References...................................17
7. Acknowledgments...............................................17
1. Introduction
Certificate transparency (CT) is a set of mechanisms designed to
deter, detect, and facilitate remediation of certificate mis-issuance
(as defined below). CT deters mis-issuance by encouraging CAs to
publish the certificates that they issue in a set of publically-
accessible logs. Each log uses a Merkle tree design to ensure that it
is an append-only database, and the log entries are digitally signed
by the log operator. Monitoring of logs detects mis-issuance.
Remediation of mis-issuance is effected via certificate revocation.
In the context of CT, the term mis-issuance refers to violations of
either semantic or syntactic constraints associated with certificates
[draft-trans-threat-analysis]. The fundamental semantic constraint
for a (Web PKI) certificate is that it was issued to an entity that
is authorized to represent the Subject name in the certificate. If
any Subject Alternative Names (SANs) are present in the certificate,
the entity also must be authorized to represent them. (It is also
assumed that the entity requested the certificate from the CA that
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issued it.) Throughout the remainder of this document we refer to a
semantically mis-issued certificate as "bogus."
A certificate is characterized as syntactically mis-issued if it
violates syntax constraints associated with the class of certificates
that it purports to represent. Syntax constraints for certificates
are established by certificate profiles, and typically are
application-specific. For example, certificates used in the Web PKI
environment might be characterized as domain validation (DV) or
extended validation (EV) certificates. Certificates issued for use
by applications such as IPsec or S/MIME have different syntactic
constraints from those issued in the Web PKI context. Throughout the
remainder of this document we refer to a syntactically mis-issued
certificate as "erroneous." From a security perspective, erroneous
certificates are not perceived as being as significant a concern as
bogus certificates.
As noted above, CT deters mis-issuance by encouraging CAs to log the
certificates that they issue. A CT log is a publicly auditable,
append-only, database of issued certificates [6962-bis] based on a
binary Merkle hash tree [Merkle]. Each CT log operates in a fashion
that enables external entities (Auditors) to detect inconsistent
behavior. As a result, logs need not be operated by trusted (third)
parties. Some forms of log misbehavior require comparing information
gleaned from multiple sources, e.g., using mechanisms such as the
ones described in [Gossip]. If an Auditor detects misbehavior by the
log, it will notify Monitors (described below) and Browser Vendors
that it serves. In turn, the Monitors and Browser Vendors are
expected to cease relying onlogs that repeatedlymisbehave in a
fashion indicative of malice. (Ultimately, what constitutes malicious
misbehavior will be determined by Monitors and Browser Vendors, and
thus is outside the scope of this document.)
A bogus certificate that has been logged will be detected by an
entity (a Monitor) that observes the log and that has knowledge of
all legitimate certificates issued to the set of certificate Subjects
that it serves. If a Monitor detects a log entry for a certificate
that is inconsistent with the reference data for a Subject, the
Monitor notifies the Subject. (A Subject may perform self-
monitoring.) Thus Monitors implement the mis-issuance detection
aspect of CT.
CAs are presumed to be deterred from logging mis-issued certificates,
because of the implied reputational consequences. (The assumption is
that a CA that is detected repeatedly mis-issuing certificates will,
in time, be blacklisted by the Browser Vendors (who control the set
of CAs that are accepted by Browsers).
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Revocation of a bogus/erroneous certificate is the primary means of
remedying mis-issuance. A browser vendor may distribute a "blacklist"
of mis-issued certificates or a bad-CA-list of certificates of CAs
that have mis-issued certificates. Browsers may then use such lists
to reject certificates on the blacklist, or certificates issued by
CAs whose certificates are on the bad-CA-list. This form of
revocation, although not codified in IETF standards, is also a means
of remediation for mis-issuance. Throughout the remainder of this
document, references to certificate revocation as a remedy encompass
these and analogous forms of revocation.
Figure 1 provides a top-level view of these elements of CT and their
interactions.
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+-----+ +----+
| Log |<--->| CA |<**********************
| | +----+ *
| | ^ *
| | * +++++++++++++++++++ * ++++++
| | v v * +
| | +---------+ * +
| |<--->| Subject |<************* * +
| | +---------+ * * +
| | ^ ^ ^ * * +
| | * + ****** * * +
| | v v * * * +
| | +---------+ * * * +
| |<--->| Browser | * * * +
| | +---------+ * * * +
| | ^ ^ * * * +
| | * ++++ * ++++++++ * + * +++ +
| | v v * * + +
| | +----------------+ * * + +
| |<***>| Browser Vendor |<*** * * + +
| | +----------------+ * * * + +
| | v v v + +
| | +---------+ + +
| |<---------------------->| Monitor | + +
| | +---------+ + +
| | ^ ^ + +
| | + * +++++ +
| | v v v +
| | +---------+ +
| |<---------------------->| Auditor |<+++++
+-----+ +---------+
Legend:
<---> Interface defined by CT
<***> Interface out of scope for CT
<+++> Proposed in Experimental Gossip Design
Figure 1 Elements of the CT Architecture
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
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2. Beneficiaries of CT
There are three classes of beneficiaries of CT: certificate Subjects,
TLS Clients, and Certification Authorities (CAs). In the initial
context of CT, the Web PKI, Subjects are web sites and TLS Clients
are Browsers employing HTTPS to access these web sites. CAs are the
issuers of certificates used in the Web PKI context.
A certificate Subject benefits from CT because CT enables Monitors to
detect certificates that have been mis-issued in the name of that
Subject. A Subject learns of a bogus/erroneous certificate (issued in
its name), via a Monitor, as noted above. (The Monitor function may
be provided by the Subject itself, i.e., self-monitoring, or by a
third party trusted by the Subject.) When a Subject is informed of
certificate mis-issuance by a Monitor, the Subject is expected to
request/demand revocation of the bogus/erroneous certificate by the
issuing CA and/or by the browser vendors (if the CA refuses to revoke
the certificate).
A Subject also may benefit from the Monitor element of CT even if the
Subject's legitimate certificate(s) has(have) not been logged. If the
bogus/erroneous certificate is logged and if a Monitor has been
provided with reference data from the Subject, then monitoring of
logs for certificates issued in the Subject's name suffices to detect
an instance of mis-issuance targeting the Subject. (If a CA operates
a Monitor on behalf of its Subjects, then the CA has the requisite
information to detect bogus/erroneous certificates in logs that it
observes.)
A TLS client (Browser) benefits from CT if the TLS client rejects a
mis-issued certificate, i.e., treats the certificate as invalid. A
TLS client is protected from accepting a mis-issued certificate if
that certificate is revoked, and if the TLS client checks the
revocation status of the certificate. (A TLS client also is protected
if a browser vendor "blacklists" a certificate or a CA as noted
above.) A TLS client also may benefit from CT if the client validates
a Signed Certificate Timestamp (SCT) [6962-bis] associated with a
certificate, and rejects the certificate if the SCT is invalid.
CAs are also CT beneficiaries. If one CA issues a legitimate
certificate to a Subject, and another CA issues a bogus certificate,
the second certificate can be detected by a Monitor (if the bogus
certificate has been logged). In this fashion the CA that issued the
legitimate certificate benefits, since the bogus certificate is
detected and, presumably revoked. Even the CA that issued the bogus
certificate is a potential beneficiary. If the bogus certificate was
issued as a result of an error or an (undetected) attack, CT can help
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the CA become aware of the error or attack and act accordingly. This
is presumed to be beneficial to the reputation of this CA.
3. The Elements of the CT Architecture
There are six elements of the CT architecture: logs, CAs, Monitors,
Subjects, TLS clients (especially browsers and browser vendors), and
Auditors. CAs, Subjects, and TLS clients are pre-existing elements
affected by CT if they choose to participate. Because not all CAs,
Subjects, and TLS clients may choose to participate in CT, these
elements are qualified as "CT-aware" to distinguish them from
existing instances of these types of Web PKI elements. Logs,
Monitors, and Auditors are new elements introduced by CT and thus
they are intrinsically CT "aware". Figure 2 shows how all of these
elements interact with the central CT element, the log. Figure 3
shows how the pre-existing elements interact with one another under
CT. Figure 4 shows the interactions of monitors and auditors that are
not covered by Figure 2.
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+-----+ +---------------+
| Log |<- add-chain or add-pre-chain -----| CA or Subject |
| |-- SCT for the new entry --------->| |
| |<- get-proof-by-hash --------------| |
| |-- inclusion proof for the entry ->| |
| | +---------------+
| | +---------+
| |<- get-sth [1] ------| Monitor |
| |-- current STH ----->| |
| |<- get-entries [1] --| |
| |-- log entries ----->| |
| | +---------+
| | +---------+
| |<- get-proof-by-hash [2] --| Browser |
| |-- inclusion proof [2] --->| |
| | +---------+
| | +----------------+
| |<- get log metadata --| Browser Vendor |
| |-- log metadata ----->| |
| | +----------------+
| | +-----------------+
| | | Auditor |
| | |+---------------+|
| |<- get-sth [1] --------------|| MMD checking ||
| |-- current STH ------------->|| ||
| |<- get-entries [1] ----------|| ||
| |-- log entries ------------->|| ||
| | |+---------------+|
| |<- get-sth ------------------|| STH frequency ||
| |-- current STH ------------->|| checking ||
| | |+---------------+|
| |<- get-sth [1] --------------|| Append-only ||
| |-- current STH ------------->|| checking ||
| |<- get-entries [1] ----------|| ||
| |-- log entries ------------->|| ||
| |<- get-sth-consistency [3] --|| ||
| |-- consistency proof ------->|| ||
+-----+ |+---------------+|
+-----------------+
[1] The get-sth operation is performed periodically, and get-entries
is performed each time a new STH is available.
[2] See Section 3.5 for privacy and performance caveats.
[3] If the Auditor stores copies of all Log entries, then this
operation is not needed.
Figure 2 Interactions with a Log
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+---------+ +---------+
| Browser |-- log metadata[1] ------------------------->| Browser |
| Vendor |-- revocation information[1] --------------->| |
| | | |
| | +---------+ | |
| | / request \--| Subject | | |
| | | to | | | | |
| | | blacklist | | | | |
| | | a CA or | | | | |
| |<-\ EE cert / | | | |
+---------+ | | | |
| | | |
+----+ | | | |
| CA | / certificate \-----| | | |
| |<-\ request / | | | |
| |-- certificate[2] ->| | | |
| | | | | |
| | / request \---| | | |
| | | revocation of | | | | |
| |<-\ a certificate / | | | |
+----+ | | | |
| | / TLS \---| |
| |<-\ connection / | |
| |-- certificate ->| |
| |-- SCT[3] ------>| |
| |<- HTTPS ------->| |
+---------+ +---------+
[1] Not subject to standardization.
[2] Optionally including SCTs in an extension.
[3] Optional, via an OCSP response or in a TLS extension.
Figure 3 Interfaces of Pre-existing Elements
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+---------+ +---------+
| Monitor |<- establish a business relationship [1] ->| Subject |
| |<- list of protected subject names --------| |
| | / per protected subject name, a \---------| |
| |<-\ list of acceptable public keys / | |
| | +---------+
| |
| | +----+
| |-- notification of mis-issuance --+-->| CA |
| | | +----+
| | |
| | | +----------------+
| | +-->| Browser Vendor |
| | +----------------+
| |
| | +---------+
| |<- notification of log mis-behavior [2] --| Auditor |
+---------+ +---------+
[1] In the case of a self-monitor, the business relationship is
trivial - the Subject and Monitor are the same organization.
[2] An entity performing the Monitor function MAY also choose to
implement some of the Auditor functions. In that case the
Monitor/Auditor interface is trivial. If the Auditor is separate, we
note that there is no interface defined at the time of this writing.
Figure 4 Monitor and Auditor Interfaces
3.1. Logs
Logs are the central elements of the CT architecture. Logging of
certificates enables Monitors to detect mis-issuance and,
subsequently, to trigger Subjects to issue revocation requests to CAs
and/or browser vendors and to notify CAs and browser vendors
directly. Logging also deters mis-issuance, as noted above. The
interfaces to a log are defined in [6962-bis], as are the details of
how a log operates.
Briefly, a certificate chain (that must be verifiable under a trust
anchor acceptable to the log) is submitted to a log by a CA, Subject
or other party. The log creates an entry for the terminal certificate
in the chain, and returns this Signed Certificate Timestamp (SCT) to
the submitter. The SCT can be conveyed to a browser in one of three
ways: it can be incorporated into a certificate by the CA that issues
it, as described later. (A CA also may submit a so-called "pre-
certificate" to a log, to acquire an SCT for inclusion in the
certificate, prior to signing the certificate.) It also can be
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conveyed explicitly in the TLS handshake or in OSCP data generated by
a CA. The SCT is a token that can be verified by browsers to
establish, to first order, that a certificate has been logged. See
[6962-bis] for additional details of SCTs.
All clients that interact with a log require access to metadata
associated with each log upon which they rely. This metadata includes
the URL and public key for the log, the list of trust anchors
accepted by the log, the hash and signature algorithms employed, etc.
Log metadata is made available to log clients via out of band means
that are generally outside the scope of the CT specifications. In the
Web PKI context, CT assumes that browser vendors will make the
necessary log metadata available to browsers via the same mechanisms
used to convey trust anchor (and vendor-managed revocation data). Log
metadata provided via this channel is not mutable by log operators
(since it is part of browser configuration data), with one exception.
When a log ceases operation, it publishes its final STH, enabling
clients to verify previous log entries and to detect any
(unauthorized) additions to the log. See [6962-bis] for additional
details.
An open question is how other log clients receive the metadata they
require to interact with the log in a predictable fashion. For
example, a log may elect to check the syntax of certificates relative
to [RFC5280], or it may skip some of all of the checks specified
there. Absent a way to determine what checks a log will perform on
submitted certificates, a CA (or other submitter) has no way to know
whether a submitted certificate will be accepted by a given log.
Similarly, a Monitor needs to acquire log metadata so that the
Monitor can locate the log and verify the signatures on log entries.
3.2. CT-aware Certification Authorities (CAs)
A (CT-aware) CA interacts with a log to submit a certificate (or a
pre-certificate) to create a log entry. (Most logged certificates are
expected to be end-entity certificates, each associated with the web
site that it represents. However, it also is possible to log a CA
certificate under certain circumstances. See Section 3.2.3 of [6962-
bis].) The pre-certificate capability is offered to facilitate rapid
deployment of CT. It has the advantage that web sites need not make
any software changes to acquire one or more SCTs, because the SCTs
are embedded in the certificate itself. There is, however, a downside
of embedding SCTs in certificates. If a log that provided an SCT is
compromised or otherwise becomes unacceptable to browsers and
Monitors, the certificate associated with that SCT will have to be
re-issued with a replacement SCT. Thus, in the long term, other
options for conveying an SCT, i.e., via the TLS handshake or in an
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OCSP response (perhaps "stapled" into the handshake [RFC6961]), are
preferred [TLS-Server].
A CA also may submit a "name-redacted" pre-certificate to a log. A
name-redacted pre-certificate includes one or more "?" labels in lieu
of DNS name components. See Section 4.2 of [6962-bis] for more
details. Name-redaction is a feature of CT designed to enable an
organization to request a CA to log its certificates without
revealing all of the DNS name components in the certificate that will
be matched to the log entry. This is an attractive feature for
organizations that want to benefit from CT without revealing internal
server names as a side effect of logging. An end-entity certificate
that is to be treated as logged via this mechanism contains a
critical (X.509v3) extension that indicates which labels have been
redacted in the log entry. This extension is needed to enable TLS
clients and Monitors to match a received certificate against the
corresponding log entry in an unambiguous fashion. See Section <TBD>
of [CA-Subject] for more details.
The CT architecture does not mandate a specific number of SCTs that
should be associated with a certificate. Browser vendors might
establish requirements for the minimum number of associated SCTs in
different contexts, but such requirements are outside the scope of
the CT architecture.
[CA-Subject] describes the requirements imposed on CT-enabled CAs.
3.3. Monitors
The primary role of a Monitor is to observe a set of logs, looking
for log entries of interest. A Subject may act as a self-monitor, or
may make use of the services of a third-party Monitor, as noted
earlier.
In the self-monitoring context, log entries of interest are ones that
contain a Subject or Subject Alternative Name (SAN) associated with
the Subject's web site(s). (Name-constrained CA certificates and
wildcard certificates also have to be examined to detect certificates
that would match the end-entity certificates associated with a
Subject's web sites.) Whenever a certificate of interest is detected,
the Subject compares it with the public key information associated
with its certificate(s). If there is a mismatch, this indicates that
this logged certificate was mis-issued. The Subject contacts the CA
that issued the certificate (using the Issuer name in the
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certificate) and requests revocation of the mis-issued certificate,
to resolve the problem. (The means by which a Subject determines how
to contact a CA based on the issuer name is outside the scope of the
CT architecture.) The means by which a Subject determines which set
of logs to watch also is outside the scope of the CT architecture. It
is anticipated that there will be a small number of logs that are
widely used, and that the metadata for these logs will be available
from browser vendors.
A third-party Monitor watches for certificates of interest to its
clients. Each client of a third party Monitor supplies the Monitor
with a list of Subject names and SANs associated with the client's
web site(s), and public key information associated with each name.
(As a special case, if a CA offers a Monitor service to its clients,
then the CA/Monitor already has this information.) The Monitor
watches a set of logs looking for entries that match the client
certificates of interest. If it detects an apparent mis-issued
certificate, the Monitor contacts the client and forwards the log
entry, along with log metadata. The client (Subject) then follows the
procedure noted above to request revocation of the mis-issued
certificate.
Note that a Monitor does not try to detect mis-behavior by a log.
That is the responsibility of an Auditor. [Monitor-Auditor] defines
the requirements for a Monitor (self of third-party) and discusses
additional operational details.
Note also that CT does not include any mechanisms designed to detect
misbehavior by a Monitor. A self-Monitor does not require such
mechanisms; Subjects who elect to rely upon third-party Monitors
would benefit from such mechanisms. See [Monitor-Auditor] for the
requirements imposed on Monitors by CT and for a more detailed
description of how a Monitor operates.
3.4. CT-aware Subjects (TLS web servers)
A (CT-aware) Subject (e.g., a web site operator) can submit its
certificate(s) to a log, and acquire an SCT for each certificate it
submits (see Section 4.1 of [6962-bis]). There are three reasons why
a Subject may choose to log its own certificate(s): (1) its CA did
not embed an SCT in the certificate(s) it issued to the Subject, (2)
the Subject wants to acquire SCTs from additional logs, or (3) the
Subject wants the flexibility offered by conveying SCTs (from logs of
its choosing) in the TLS handshake. [CA-Subject] describes the
requirements imposed on Subjects for delivery of SCTs to CT-aware TLS
clients.
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Every Subject should either perform self-monitoring, or become a
client of a third-party Monitor so that bogus certificates issued in
the name of the Subject will be detected. When a Subject is notified
of a bogus certificate issued in its name, the Subject contacts the
CA that issued the certificate and requests that it be revoked, using
whatever mechanisms the CA provides for such requests. The Subject
may also contact browser vendors and ask that they put the
certificate on a blacklist of mis-issued certificates or put the CA's
certificate on a bad-CA-list, if the CA refuses to revoke the bogus
certificate. [CA-Subject] describe the requirements established for
for CT-aware Subjects.
3.5. CT-aware TLS clients (web browsers)
As noted in Section 2, a TLS client can benefit from CT even without
actively participating. A Monitor will detect a mis-issued, logged
certificate and notify the affected Subject. The Subject will, in
turn attempt to trigger revocation by the CA that mis-issued the
certificate in question, ultimately asking browser vendors to
blacklist the certificate (or the CA) if revocation is not effected.
Thus a TLS client that processes certificate revocation status data,
e.g., CRLs, OCSP responses, will be protected from bogus certificates
that have been logged, detected, and revoked.
If a TLS client required that every certificate it accepted was
accompanied by an SCT, the client could have some confidence that the
certificate had been logged. This would increase confidence that the
certificate, if it were mis-issued, would have been revoked. However,
there are two problems with mandating that every TLS client reject
(treat as invalid) any certificate that is not accompanied by an SCT.
First, such behavior does not accommodate incremental deployment of
CT. Second, the mere presence of an SCT is not a guarantee that the
certificate has been logged.
To have high confidence that a certificate has been logged, a TLS
client would have to verify that a log entry exists for the
certificate. This requires acquisition of an inclusion proof from the
log (see Section 4.5 of [6962-bis]). Requesting an inclusion proof
directly from a log for a certificate discloses to a log that the TLS
client is interested in the certificate in question. For a browser,
this would disclose which web sites a user was visiting, a potential
privacy concern for many users. Also, the data acquisition and
processing might pose an unacceptable burden for some TLS clients,
(e.g., browsers), and might not be performed in realtime anyway. Thus
CT-aware TLS clients are not expected to fetch an inclusion proof in
realtime, e.g., during TLS connection establishment. Such clients
also are not expected to reject a certificate that has no associated
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SCT, because there is no plan for incremental deployment of CT that
accommodates such rejection in a backwards compatible fashion.
Nonetheless, if an SCT is provided with a certificate, a CT-aware TLS
client could verify the signature and the SCT data for the
certificate in question. If performing these checks would not impose
an undue burden on the TLS client, the checks would help detect
errors in SCTs and provided feedback to log operators (via Subjects).
A TLS client that is a browser might discriminate against a
certificate presented for a web site if the certificate is not
accompanied by an SCT, e.g., providing an indication of this via the
user interface. See [browser-vendor] for the requirements established
for CT-aware browsers and browser vendors.
3.6. Auditors
Auditors perform checks intended to detect mis-behavior by logs.
There are four log behavior properties that Auditors check:
1. The Maximum Merge Delay (MMD)
2. The STH Frequency Count
3. The append-only property
4. The consistency of the log view presented to all query sources
The first three of these checks are easily performed using existing
log interfaces and log metadata (see [6962-bis]). For example, an
Auditor could submit a certificate to a log and request an STH after
the indicated MMD, to verify that the log is achieving its advertised
MMD. The last check is more difficult to perform because it requires
a way to share log responses among a set of CT elements, perhaps
including browsers, web sites, Monitors, and Auditors, e.g., using
so-called gossiping [Gossip]. There is as yet no standard for
gossiping and thus the last check is NOT part of Auditor requirements
at this time. See [Monitor-Auditor] for additional details of Auditor
operation.
4. Security Considerations
CT is a system created to improve security for X.509 public key
certificates, especially in the Web PKI context. An attack analysis
[draft-trans-threat-analysis] examines the types of attacks that can
be mounted against CT, to effect mis-issuance, and how CT addresses
(or fails to address) each type of attack. That analysis is based on
the architecture described in this document, and thus readers of this
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document are referred to that one for a thorough discussion of the
security aspects of CT. Briefly, CT logs represent a viable means of
deterring semantic mis-issuance of certificates. Monitors are an
effective way to detect semantic mis-issuance of logged certificates.
The CT architecture enables certificate Subjects to request
revocation of mis-issued certificates, thus remedying such mis-
issuance. Residual vulnerabilities exist with regard to some forms of
log and Monitor misbehavior, because the architecture does not
include normative means of detecting such behavior. The current
design also does not ensure the ability of Monitors to detect
syntactic mis-issuance of certificates. This is because provisions
for asserting the type of certificate being issued, for inclusion in
an SCT, have not been standardized.
5. IANA Considerations
<TBD>
6. References
6.1. Normative References
[Merkle] Merkle, R. C. (1988). "A Digital Signature Based on a
Conventional Encryption Function." Advances in Cryptology -
CRYPTO '87. Lecture Notes in Computer Science 293. p. 369
[6962-bis] Laurie, B., Langley, A., Kasper, E., Messeri, E., and R.
Stradling, "Certificate Transparency," draft-ietf-trans-
rfc6962-bis-10 (work in progress), October 2015.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008.
[RFC6066] Eastlake 3rd, D., "Transport Layer Security (TLS)
Extensions: Extension Definitions", RFC 6066, January 2011.
[RFC6960] Santesson, S., Myers, M., Ankney, R., Malpani, A.,
Galperin, S., and C. Adams, "X.509 Internet Public Key
Infrastructure Online Certificate Status Protocol - OCSP",
RFC 6960, June 2013.
[RFC6961] Pettersen, Y., "The Transport Layer Security (TLS) Multiple
Certificate Status Request Extension," RFC 6961, June 2013.
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6.2. Informative References
[draft-trans-threat-analysis] Kent, S., "Attack Model and Threat for
Certificate Transparency," draft-ietf-trans-threat-
analysis-03 (work in progress), October 2015.
[Gossip] Nordberg, L., Gillmor, D., and Ritter, T., "Gossiping in
CT," draft-ietf-trans-gossip-01 (work in progress), October
2015.
[Monitor-Auditor] <TBD>
[CA-Subject] <TBD>
[browser-vendor] <TBD>
7. Acknowledgments
<TBD>
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Authors' Addresses
Stephen Kent
unaffiliated
Email: kent@alum.mit.edu
David Mandelberg
unaffiliated
Email: david@mandelberg.org
Karen Seo
unaffiliated
Email: karensseo@gmail.com
Kent, et al. Expires June 12, 2018 [Page 18]
