wdiff draft-ietf-tls-cached-info-10.txt draft-ietf-tls-cached-info-11.txt

TLS S. Santesson
Internet-Draft 3xA Security AB
Intended status: Standards Track H. Tschofenig
Expires: June 16, 28, 2012 Nokia Siemens Networks
December 14, 26, 2011

Transport Layer Security (TLS) Cached Information Extension
draft-ietf-tls-cached-info-10.txt
draft-ietf-tls-cached-info-11.txt

Abstract

This document defines a

Transport Layer Security (TLS) extension for
cached information. handshakes often include fairly static
information, such as the server certificate and a list of trusted
Certification Authorities (CAs). This information can be of
considerable size, particularly if the server certificate is bundled
with a complete certificate path (including all intermediary
certificates up to the trust anchor public key).

This document defines an extension allows that omits the exchange of already
available information. The TLS client to inform informs a server of cached information
information, for example from a previous TLS handshakes, handshake, allowing the
server to omit sending cached static information to the client
during the TLS handshake protocol exchange. already available information.

Status of this Memo

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provisions of BCP 78 and BCP 79.

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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Cached Information Extension . . . . . . . . . . . . . . . . . 5
4. Extension Exchange . . Specification . . . . . . . . . . . . . . . . . . . . 7
4.1. Cached Information . . . . . . . . . Fingerprint of the Certificate Chain . . . . . . . . . . . 7
4.2. Reconnaissance . . . . . . . Fingerprint for Trusted CAs . . . . . . . . . . . . . . . 7 8
5. Cached Information Substitution . . . Security Considerations . . . . . . . . . . . . 8
5.1. Substitution Syntax for certificate_chain . . . . . . . 10
6. IANA Considerations . 8
5.2. Substitution Syntax for trusted_cas . . . . . . . . . . . 9
6. Security Considerations . . . . . . . . . 11
6.1. New Entry to the TLS ExtensionType Registry . . . . . . . 11
6.2. New Registry for CachedInformationType . . . 10
7. IANA Considerations . . . . . . . 11
6.3. New Registry for HashAlgorithm . . . . . . . . . . . . . . 11
8.
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 12
9.
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
9.1.
8.1. Normative References . . . . . . . . . . . . . . . . . . . 13
9.2.
8.2. Informative References . . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14

1. Introduction

TLS

Transport Layer Security (TLS) handshakes often include fairly static information
information, such as the server certificate and a list of trusted
Certification Authorities (CAs).
Static This information such as a server certificate can be of
considerable size. This is the case in particular size, particularly if the server certificate is bundled
with a complete certificate path, including path (including all intermediary
certificates up to the trust anchor public key.

Significant benefits can be achieved key).

Optimizing the exchange of information to a minimum helps to improve
performance in environments where devices are connected to a network
with characteristics like low bandwidth and bandwidth, high latency networks, in particular if the communication channel also has
a relatively and high rate loss
rate. These types of transmission errors, if networks exist, for example, when smart objects
are connected using a known and
previously cached server certificate path can be omitted from low power IEEE 802.15.4 radio. For more
information about the TLS
handshake. challenges with smart object deployments please
see [I-D.iab-smart-object-workshop].

This specification defines the Cached Information a TLS extension,
which may be used by extension that allows a client and a
server to exclude transmission of cached information from the TLS
handshake.

2. Terminology

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL "MUST", "MUST NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].

3. Cached Information Extension

This document defines a new extension type (cached_information(TBD)) (cached_information(TBD)),
which is defined and used in
both the client hello and server hello messages. The
extension type is specified as follows.

enum {
cached_information(TBD), (65535)
} ExtensionType;

The extension_data field of this extension, when included in the
client hello, SHALL MUST contain CachedInformation according to the
following structure: CachedInformation structure.

enum {
certificate_chain(1), trusted_cas(2), trusted_cas(2) (255)
} CachedInformationType;

struct {
CachedInformationType type;
HashAlgorithm hash;
opaque hash_value<1..255>;
} CachedObject;

struct {
CachedObject cached_info<1..2^16-1>;
} CachedInformation;

When the CachedInformationType identifies a certificate_chain, then
the hash_value field MUST include a hash calculated over the
certificate_list element of a server side Certificate message,
excluding the three length bytes of the certificate_list vector.

When the CachedInformationType identifies a trusted_cas, then the
hash_value MUST include a hash calculated over the
certificate_authorities element of a server side CertificateRequest
message, excluding the two length bytes of the
certificate_authorities vector.

The hash algorithm used to calculate hash values SHALL be the hash
algorithm that was used to generate the Finished message is conveyed in the
handshake exchange from which
'hash' field of the hashed information was cached.
Hash algorithm identifiers are defined in CachedObject element. This document defines the
following hash algorithms:

o SHA-1: NIST FIPS PUB 180-3 [SHA]
o SHA-224: RFC 5246 [RFC5246]
HashAlgorithm registry.

Other specifications MAY define more 3874 [RFC3874]

o SHA-256: NIST FIPS PUB 180-3 [SHA]

o SHA-384: NIST FIPS PUB 180-3 [SHA]

o SHA-512: NIST FIPS PUB 180-3 [SHA]

This document establishes a registry for CachedInformationType types. types
and additional values can be added following the policy described in
Section 6.

4. Extension Exchange

4.1. Cached Information Specification

Clients supporting this extension MAY include a the
"cached_information" extension in the (extended) client hello, which
MAY contain zero or more cached
objects (CachedObject).

Servers that receive an extended client hello containing a
"cached_information" CachedObject attributes.

Server supporting this extension MAY indicate that they support cached
information objects by including a cached_information include the "cached_information"
extension in
their (extended) server hello.

A cached_information extension provided in the (extended) server hello has hello, which MAY contain one or
more CachedObject attributes. By returning the
following semantics:

o An empty cached_information "cached_information"
extension indicates that the server
supports information caching but provides no information about
what information types it supports.

o A non-empty cached information extension indicates that the server 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
depending on other information in the Client Hello that modify what
values the server uses, in particular the Server Name Indication
[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,
the server MAY substitute send fingerprints of the cached information in the
handshake exchange with as a matching CachedObject from the client hello
"cached_information" extension.

A substitution syntax that defines how replacement for the CachedObject structure is
carried in exchange of the handshake message MUST be defined for each
CachedInformationType in a way that does not violate full
data. Section 4.1 and Section 4.2 defines the syntax of the handshake message. The substitution syntax for
certificate_chain(1) and trusted_cas(2) is provided below.
fingerprinted information.

The handshake protocol SHALL MUST proceed using the cached information as if it
was provided in the handshake protocol. The Finished message
SHALL MUST be
calculated over the actual data exchanged in the handshake protocol.
That is, the Finished message will be calculated over the hash values
of cached information objects and not over the cached information
that were omitted from transmission.

The server MUST NOT include more than one CachedObject as
substitution fingerprint for a single
information element, i.e., at maximum only one CachedObject structure
per replaced information is provided.

4.1. Fingerprint of the cached information.

5.1. Substitution Syntax for certificate_chain Certificate Chain

When an object of type certificate_chain 'certificate_chain' is provided in the client
hello, the server MAY substitute the cached information with send a
matching hash value received from the client by expanding fingerprint instead of the
Certificate handshake message complete
certificate chain as follows.

Original shown below.

The original handshake message syntax is defined in RFC 5246 [RFC5246]:
[RFC5246] and has the following structure:

opaque ASN.1Cert<1..2^24-1>;

struct {
ASN.1Cert certificate_list<0..2^24-1>;
} Certificate;

Substitution syntax

By using the extension defined in this document the following
information is sent:

struct {
CachedObject ASN.1Cert<1..2^24-1>;
} Certificate;

The opaque ASN.1Cert structure is replaced with the CachedObject
structure defined by expanding in this document.

Note: [I-D.wouters-tls-oob-pubkey] allows a PKIX certificate
containing only the syntax SubjectPublicKeyInfo instead of the opaque full
information typically found in a certificate. Hence, when this
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 structure:

CachedObject ASN.1Cert<1..2^24-1>;

5.2. Substitution Syntax with the mentioned raw public key.

4.2. Fingerprint for trusted_cas Trusted CAs

When a hash for an object of type trusted_cas 'trusted_cas' is provided in the
client hello, the server MAY substitute the cached information with send a
matching hash value received from the client by expanding fingerprint instead of the
CertificateRequest handshake message
complete certificate authorities information as follows.

Original shown below.

The original handshake message syntax is defined in RFC 5246 [RFC5246]:
[RFC5246] and has the following structure:

opaque DistinguishedName<1..2^16-1>;

struct {
ClientCertificateType certificate_types<1..2^8-1>;
SignatureAndHashAlgorithm
supported_signature_algorithms<2^16-1>;
DistinguishedName certificate_authorities<0..2^16-1>;
} CertificateRequest

The substitution syntax is defined by expanding CertificateRequest;

By using the syntax of extension defined in this document the following
information is sent:

struct {
ClientCertificateType certificate_types<1..2^8-1>;
SignatureAndHashAlgorithm
supported_signature_algorithms<2^16-1>;
CachedObject DistinguishedName<1..2^16-1>;
} CertificateRequest;

The opaque DistinguishedName structure: structure is replaced with the
CachedObject DistinguishedName<1..2^16-1>;

6. structure defined in this document.

5. Security Considerations

The hash algorithm used in this specification is required to have
reasonable random properties in order to provide reasonably unique
identifiers. There is no clearly identified requirement that this hash algorithm must
have strong collision resistance. However since
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
handshake) and sending a hash of that cached information in an
unencrypted handshake might introduce integrity or data disclosure
issues as it enables an attacker to identify if a known object (such
as a known server certificate) has been used in previous encrypted
handshakes. Information object types defined in this specification,
such as server certificates, are public objects and usually not
sensitive in this regard, but implementers should be aware if any
cached information are subject to such security concerns and in such
case SHOULD NOT send a hash over encrypted data in en unencrypted
handshake.

6. IANA Considerations

1) Create

6.1. New Entry to the TLS ExtensionType Registry

IANA is requested to add an entry, cached_information(TBD), in entry to the existing registry
for TLS ExtensionType (defined
registry, defined in RFC 5246 [RFC5246]).

2) Establish [RFC5246], for cached_information(TBD)
defined in this document.

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) and
trusted_cas(2). TLS CachedInformationType

o trusted_cas(2)

The policy for adding new values in to this registry, following the inclusive
range 0-63 (decimal) are assigned via
terminology defined in RFC 5226 [RFC5226] [RFC5226], is as follows:

o 0-63 (decimal): Standards
Action. Values from the inclusive range Action

o 64-223 (decimal) are
assigned via RFC 5226 (decimal): Specification Required. Values from the
inclusive range Required

o 224-255 (decimal) are (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.

8. Use

7. Acknowledgments

The author acknowledges input from many members of the TLS working
group.

We would like to thank Paul Wouters for his feedback and Nikos
Mavrogiannopoulos for his document review in December 2011.

8. References

9.1.

8.1. Normative References

[I-D.ietf-tls-rfc4366-bis]
3rd, D., "Transport Layer Security (TLS) Extensions:
Extension Definitions", draft-ietf-tls-rfc4366-bis-12
(work in progress), September 2010.

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
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
(TLS) Protocol Version 1.2", RFC 5246, August 2008.

9.2.

[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
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.

Authors' Addresses

Stefan Santesson
3xA Security AB
Scheelev. 17
Lund 223 70
Sweden

Email: sts@aaa-sec.com

Hannes Tschofenig
Nokia Siemens Networks
Linnoitustie 6
Espoo 02600
Finland

Phone: +358 (50) 4871445
Email: Hannes.Tschofenig@gmx.net
URI: http://www.tschofenig.priv.at