draft-ietf-tls-cached-info-10.txt   draft-ietf-tls-cached-info-11.txt 
TLS S. Santesson TLS S. Santesson
Internet-Draft 3xA Security AB Internet-Draft 3xA Security AB
Intended status: Standards Track H. Tschofenig Intended status: Standards Track H. Tschofenig
Expires: June 16, 2012 Nokia Siemens Networks Expires: June 28, 2012 Nokia Siemens Networks
December 14, 2011 December 26, 2011
Transport Layer Security (TLS) Cached Information Extension Transport Layer Security (TLS) Cached Information Extension
draft-ietf-tls-cached-info-10.txt draft-ietf-tls-cached-info-11.txt
Abstract Abstract
This document defines a Transport Layer Security (TLS) extension for Transport Layer Security (TLS) handshakes often include fairly static
cached information. This extension allows the TLS client to inform a information, such as the server certificate and a list of trusted
server of cached information from previous TLS handshakes, allowing Certification Authorities (CAs). This information can be of
the server to omit sending cached static information to the client considerable size, particularly if the server certificate is bundled
during the TLS handshake protocol exchange. with a complete certificate path (including all intermediary
certificates up to the trust anchor public key).
This document defines an extension that omits the exchange of already
available information. The TLS client informs a server of cached
information, for example from a previous TLS handshake, allowing the
server to omit the already available information.
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 June 16, 2012. This Internet-Draft will expire on June 28, 2012.
Copyright Notice Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the Copyright (c) 2011 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
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to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
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the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Cached Information Extension . . . . . . . . . . . . . . . . . 5 3. Cached Information Extension . . . . . . . . . . . . . . . . . 5
4. Extension Exchange . . . . . . . . . . . . . . . . . . . . . . 7 4. Exchange Specification . . . . . . . . . . . . . . . . . . . . 7
4.1. Cached Information . . . . . . . . . . . . . . . . . . . . 7 4.1. Fingerprint of the Certificate Chain . . . . . . . . . . . 7
4.2. Reconnaissance . . . . . . . . . . . . . . . . . . . . . . 7 4.2. Fingerprint for Trusted CAs . . . . . . . . . . . . . . . 8
5. Cached Information Substitution . . . . . . . . . . . . . . . 8 5. Security Considerations . . . . . . . . . . . . . . . . . . . 10
5.1. Substitution Syntax for certificate_chain . . . . . . . . 8 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
5.2. Substitution Syntax for trusted_cas . . . . . . . . . . . 9 6.1. New Entry to the TLS ExtensionType Registry . . . . . . . 11
6. Security Considerations . . . . . . . . . . . . . . . . . . . 10 6.2. New Registry for CachedInformationType . . . . . . . . . . 11
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 6.3. New Registry for HashAlgorithm . . . . . . . . . . . . . . 11
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 12 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 12
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
9.1. Normative References . . . . . . . . . . . . . . . . . . . 13 8.1. Normative References . . . . . . . . . . . . . . . . . . . 13
9.2. Informative References . . . . . . . . . . . . . . . . . . 13 8.2. Informative References . . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14
1. Introduction 1. Introduction
TLS handshakes often include fairly static information such as server Transport Layer Security (TLS) handshakes often include fairly static
certificate and a list of trusted Certification Authorities (CAs). information, such as the server certificate and a list of trusted
Static information such as a server certificate can be of Certification Authorities (CAs). This information can be of
considerable size. This is the case in particular if the server considerable size, particularly if the server certificate is bundled
certificate is bundled with a complete certificate path, including with a complete certificate path (including all intermediary
all intermediary certificates up to the trust anchor public key. certificates up to the trust anchor public key).
Significant benefits can be achieved in low bandwidth and high Optimizing the exchange of information to a minimum helps to improve
latency networks, in particular if the communication channel also has performance in environments where devices are connected to a network
a relatively high rate of transmission errors, if a known and with characteristics like low bandwidth, high latency and high loss
previously cached server certificate path can be omitted from the TLS rate. These types of networks exist, for example, when smart objects
handshake. are connected using a low power IEEE 802.15.4 radio. For more
information about the challenges with smart object deployments please
see [I-D.iab-smart-object-workshop].
This specification defines the Cached Information TLS extension, This specification defines a TLS extension that allows a client and a
which may be used by a client and a server to exclude transmission of server to exclude transmission of cached information from the TLS
cached information from the TLS handshake. handshake.
2. Terminology 2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "MUST", "MUST NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
3. Cached Information Extension 3. Cached Information Extension
A new extension type (cached_information(TBD)) is defined and used in This document defines a new extension type (cached_information(TBD)),
both the client hello and server hello messages. The extension type which is used in client hello and server hello messages. The
is specified as follows. extension type is specified as follows.
enum { enum {
cached_information(TBD), (65535) cached_information(TBD), (65535)
} ExtensionType; } ExtensionType;
The extension_data field of this extension, when included in the The extension_data field of this extension, when included in the
client hello, SHALL contain CachedInformation according to the client hello, MUST contain the CachedInformation structure.
following structure:
enum { enum {
certificate_chain(1), trusted_cas(2), (255) certificate_chain(1), trusted_cas(2) (255)
} CachedInformationType; } CachedInformationType;
struct { struct {
CachedInformationType type; CachedInformationType type;
HashAlgorithm hash; HashAlgorithm hash;
opaque hash_value<1..255>; opaque hash_value<1..255>;
} CachedObject; } CachedObject;
struct { struct {
CachedObject cached_info<1..2^16-1>; CachedObject cached_info<1..2^16-1>;
} CachedInformation; } CachedInformation;
When CachedInformationType identifies certificate_chain, then When the CachedInformationType identifies a certificate_chain, then
hash_value MUST include a hash calculated over the certificate_list the hash_value field MUST include a hash calculated over the
element of a server side Certificate message, excluding the three certificate_list element of a server side Certificate message,
length bytes of the certificate_list vector. excluding the three length bytes of the certificate_list vector.
When CachedInformationType identifies trusted_cas, then hash_value When the CachedInformationType identifies a trusted_cas, then the
MUST include a hash calculated over the certificate_authorities hash_value MUST include a hash calculated over the
element of a server side CertificateRequest message, excluding the certificate_authorities element of a server side CertificateRequest
two length bytes of the certificate_authorities vector. message, excluding the two length bytes of the
certificate_authorities vector.
The hash algorithm used to calculate hash values SHALL be the hash The hash algorithm used to calculate hash values is conveyed in the
algorithm that was used to generate the Finished message in the 'hash' field of the CachedObject element. This document defines the
handshake exchange from which the hashed information was cached. following hash algorithms:
Hash algorithm identifiers are defined in the RFC 5246 [RFC5246]
HashAlgorithm registry.
Other specifications MAY define more CachedInformationType types. o SHA-1: NIST FIPS PUB 180-3 [SHA]
o SHA-224: RFC 3874 [RFC3874]
4. Extension Exchange o SHA-256: NIST FIPS PUB 180-3 [SHA]
4.1. Cached Information o SHA-384: NIST FIPS PUB 180-3 [SHA]
Clients MAY include a "cached_information" extension in the o SHA-512: NIST FIPS PUB 180-3 [SHA]
(extended) client hello, which MAY contain zero or more cached
objects (CachedObject).
Servers that receive an extended client hello containing a This document establishes a registry for CachedInformationType types
"cached_information" extension MAY indicate that they support cached and additional values can be added following the policy described in
information objects by including a cached_information extension in Section 6.
their (extended) server hello.
A cached_information extension provided in the server hello has the 4. Exchange Specification
following semantics:
o An empty cached_information extension indicates that the server Clients supporting this extension MAY include the
supports information caching but provides no information about "cached_information" extension in the (extended) client hello, which
what information types it supports. MAY contain zero or more CachedObject attributes.
o A non-empty cached information extension indicates that the server Server supporting this extension MAY include the "cached_information"
supports caching of each present CachedObject that matches the extension in the (extended) server hello, which MAY contain one or
specified hash value. The server MAY support other cached objects more CachedObject attributes. By returning the "cached_information"
that are not present in the extension. extension the server indicates that it supports caching of each
present CachedObject that matches the specified hash value. The
server MAY support other cached objects that are not present in the
extension.
Note: Clients may need the ability to cache different values Note: Clients may need the ability to cache different values
depending on other information in the Client Hello that modify what depending on other information in the Client Hello that modify what
values the server uses, in particular the Server Name Indication values the server uses, in particular the Server Name Indication
[I-D.ietf-tls-rfc4366-bis] value. [I-D.ietf-tls-rfc4366-bis] value.
4.2. Reconnaissance
A client MAY include an empty cached_information extension (with
empty extension_data field) in its (extended) client hello to query
whether the server supports cached information.
Upon receiving an empty cached_information extension, a server MAY
indicate that it supports cached information in handshakes by
including a cached_information extension in its (extended) server
hello according to any of the available options in Section 4.1.
5. Cached Information Substitution
Following a successful exchange of "cached_information" extensions, Following a successful exchange of "cached_information" extensions,
the server MAY substitute cached information in the handshake the server MAY send fingerprints of the cached information in the
exchange with a matching CachedObject from the client hello handshake exchange as a replacement for the exchange of the full
"cached_information" extension. data. Section 4.1 and Section 4.2 defines the syntax of the
fingerprinted information.
A substitution syntax that defines how the CachedObject structure is
carried in the handshake message MUST be defined for each
CachedInformationType in a way that does not violate the syntax of
the handshake message. The substitution syntax for
certificate_chain(1) and trusted_cas(2) is provided below.
The handshake protocol SHALL proceed using the cached information as The handshake protocol MUST proceed using the information as if it
if it was provided in the handshake protocol. The Finished message was provided in the handshake protocol. The Finished message MUST be
SHALL be calculated over the actual data exchanged in the handshake calculated over the actual data exchanged in the handshake protocol.
protocol. That is, the Finished message will be calculated over the That is, the Finished message will be calculated over the hash values
hash values of cached information objects and not over the cached of cached information objects and not over the cached information
information that were omitted from transmission. that were omitted from transmission.
The server MUST NOT include more than one CachedObject as The server MUST NOT include more than one fingerprint for a single
substitution for the cached information. information element, i.e., at maximum only one CachedObject structure
per replaced information is provided.
5.1. Substitution Syntax for certificate_chain 4.1. Fingerprint of the Certificate Chain
When an object of type certificate_chain is provided in the client When an object of type 'certificate_chain' is provided in the client
hello, the server MAY substitute the cached information with a hello, the server MAY send a fingerprint instead of the complete
matching hash value received from the client by expanding the certificate chain as shown below.
Certificate handshake message as follows.
Original handshake message syntax defined in RFC 5246 [RFC5246]: The original handshake message syntax is defined in RFC 5246
[RFC5246] and has the following structure:
opaque ASN.1Cert<1..2^24-1>; opaque ASN.1Cert<1..2^24-1>;
struct { struct {
ASN.1Cert certificate_list<0..2^24-1>; ASN.1Cert certificate_list<0..2^24-1>;
} Certificate; } Certificate;
Substitution syntax is defined by expanding the syntax of the opaque By using the extension defined in this document the following
ASN.1Cert structure: information is sent:
CachedObject ASN.1Cert<1..2^24-1>; struct {
CachedObject ASN.1Cert<1..2^24-1>;
} Certificate;
5.2. Substitution Syntax for trusted_cas The opaque ASN.1Cert structure is replaced with the CachedObject
structure defined in this document.
When a hash for an object of type trusted_cas is provided in the Note: [I-D.wouters-tls-oob-pubkey] allows a PKIX certificate
client hello, the server MAY substitute the cached information with a containing only the SubjectPublicKeyInfo instead of the full
matching hash value received from the client by expanding the information typically found in a certificate. Hence, when this
CertificateRequest handshake message as follows. specification is used in combination with
[I-D.wouters-tls-oob-pubkey] and the negotiated certificate type is
RawPublicKey then the TLS server sends the hashed Certificate element
that contains a ASN.1Cert with the mentioned raw public key.
Original handshake message syntax defined in RFC 5246 [RFC5246]: 4.2. Fingerprint for Trusted CAs
When a hash for an object of type 'trusted_cas' is provided in the
client hello, the server MAY send a fingerprint instead of the
complete certificate authorities information as shown below.
The original handshake message syntax is defined in RFC 5246
[RFC5246] and has the following structure:
opaque DistinguishedName<1..2^16-1>; opaque DistinguishedName<1..2^16-1>;
struct { struct {
ClientCertificateType certificate_types<1..2^8-1>; ClientCertificateType certificate_types<1..2^8-1>;
SignatureAndHashAlgorithm SignatureAndHashAlgorithm
supported_signature_algorithms<2^16-1>; supported_signature_algorithms<2^16-1>;
DistinguishedName certificate_authorities<0..2^16-1>; DistinguishedName certificate_authorities<0..2^16-1>;
} CertificateRequest } CertificateRequest;
The substitution syntax is defined by expanding the syntax of the By using the extension defined in this document the following
opaque DistinguishedName structure: information is sent:
CachedObject DistinguishedName<1..2^16-1>; struct {
ClientCertificateType certificate_types<1..2^8-1>;
SignatureAndHashAlgorithm
supported_signature_algorithms<2^16-1>;
CachedObject DistinguishedName<1..2^16-1>;
} CertificateRequest;
6. Security Considerations The opaque DistinguishedName structure is replaced with the
CachedObject structure defined in this document.
5. Security Considerations
The hash algorithm used in this specification is required to have The hash algorithm used in this specification is required to have
reasonable random properties in order to provide reasonably unique reasonable random properties in order to provide reasonably unique
identifiers. There is no clearly identified requirement that this identifiers. There is no requirement that this hash algorithm must
hash algorithm must have strong collision resistance. However since have strong collision resistance.
the hash algorithm is used to represent data in the finished
calculation, the security properties of the finished calculation will
change if a weaker hash algorithm is used to represent cached
information compared with the hash algorithm used to calculate the
finished message.
Caching information in an encrypted handshake (such as a renegotiated Caching information in an encrypted handshake (such as a renegotiated
handshake) and sending a hash of that cached information in an handshake) and sending a hash of that cached information in an
unencrypted handshake might introduce integrity or data disclosure unencrypted handshake might introduce integrity or data disclosure
issues as it enables an attacker to identify if a known object (such issues as it enables an attacker to identify if a known object (such
as a known server certificate) has been used in previous encrypted as a known server certificate) has been used in previous encrypted
handshakes. Information object types defined in this specification, handshakes. Information object types defined in this specification,
such as server certificates, are public objects and usually not such as server certificates, are public objects and usually not
sensitive in this regard, but implementers should be aware if any sensitive in this regard, but implementers should be aware if any
cached information are subject to such security concerns and in such cached information are subject to such security concerns and in such
case SHOULD NOT send a hash over encrypted data in en unencrypted case SHOULD NOT send a hash over encrypted data in en unencrypted
handshake. handshake.
7. IANA Considerations 6. IANA Considerations
1) Create an entry, cached_information(TBD), in the existing registry 6.1. New Entry to the TLS ExtensionType Registry
for ExtensionType (defined in RFC 5246 [RFC5246]).
2) Establish a registry for TLS CachedInformationType values. The IANA is requested to add an entry to the existing TLS ExtensionType
first entries in the registry are certificate_chain(1) and registry, defined in RFC 5246 [RFC5246], for cached_information(TBD)
trusted_cas(2). TLS CachedInformationType values in the inclusive defined in this document.
range 0-63 (decimal) are assigned via RFC 5226 [RFC5226] Standards
Action. Values from the inclusive range 64-223 (decimal) are
assigned via RFC 5226 Specification Required. Values from the
inclusive range 224-255 (decimal) are reserved for RFC 5226 Private
Use.
8. Acknowledgments 6.2. New Registry for CachedInformationType
IANA is requested to establish a registry for TLS
CachedInformationType values. The first entries in the registry are
o certificate_chain(1)
o trusted_cas(2)
The policy for adding new values to this registry, following the
terminology defined in RFC 5226 [RFC5226], is as follows:
o 0-63 (decimal): Standards Action
o 64-223 (decimal): Specification Required
o 224-255 (decimal): reserved for Private Use
6.3. New Registry for HashAlgorithm
IANA is requested to establish a registry for HashAlgorithm values
and to populate the registry with an initial set of values listed in
Section 3.
The policy for adding new values to this registry, following the
terminology defined in RFC 5226 [RFC5226], is as follows:
o 0-63 (decimal): Standards Action
o 64-223 (decimal): Specification Required
o 224-255 (decimal): reserved for Private Use
7. Acknowledgments
The author acknowledges input from many members of the TLS working The author acknowledges input from many members of the TLS working
group. group.
9. References We would like to thank Paul Wouters for his feedback and Nikos
Mavrogiannopoulos for his document review in December 2011.
9.1. Normative References 8. References
8.1. Normative References
[I-D.ietf-tls-rfc4366-bis] [I-D.ietf-tls-rfc4366-bis]
3rd, D., "Transport Layer Security (TLS) Extensions: 3rd, D., "Transport Layer Security (TLS) Extensions:
Extension Definitions", draft-ietf-tls-rfc4366-bis-12 Extension Definitions", draft-ietf-tls-rfc4366-bis-12
(work in progress), September 2010. (work in progress), September 2010.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3874] Housley, R., "A 224-bit One-way Hash Function: SHA-224",
RFC 3874, September 2004.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008. (TLS) Protocol Version 1.2", RFC 5246, August 2008.
9.2. Informative References [SHA] "Federal Information Processing Standards Publication
(FIPS PUB) 180-3, Secure Hash Standard (SHS)",
October 2008.
8.2. Informative References
[I-D.iab-smart-object-workshop]
Tschofenig, H. and J. Arkko, "Report from the
'Interconnecting Smart Objects with the Internet'
Workshop, 25th March 2011, Prague",
draft-iab-smart-object-workshop-06 (work in progress),
October 2011.
[I-D.wouters-tls-oob-pubkey]
Wouters, P., Gilmore, J., Weiler, S., Kivinen, T., and H.
Tschofenig, "TLS out-of-band public key validation",
draft-wouters-tls-oob-pubkey-02 (work in progress),
November 2011.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226, IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008. May 2008.
Authors' Addresses Authors' Addresses
Stefan Santesson Stefan Santesson
3xA Security AB 3xA Security AB
Scheelev. 17 Scheelev. 17
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