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

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on June 16, 28, 2012.

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   document authors.  All rights reserved.

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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

   A

   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 is conveyed in the hash
   algorithm that was used to generate the Finished message 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 extension in
   their (extended) server hello.

   A cached_information include the "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 in this document.

   Note: [I-D.wouters-tls-oob-pubkey] allows a PKIX certificate
   containing only the SubjectPublicKeyInfo instead of the 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 defined by expanding
   RawPublicKey then the syntax of TLS server sends the opaque 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.

7.

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.

9.

   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