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Versions: (draft-santesson-tls-certcache) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 RFC 7924

INTERNET-DRAFT                               S. Santesson (3xA Security)
Intended Status: Proposed Standard
Expires: September 27, 2010                               March 26, 2010


      Transport Layer Security (TLS) Cached Information Extension
                  <draft-ietf-tls-cached-info-05.txt>



Abstract

   This document defines a Transport Layer Security (TLS) extension for
   cached information. This extension allows the TLS client to inform a
   server of cached information from previous TLS sessions, allowing the
   server to omit sending cached static information to the client during
   the TLS handshake protocol exchange.


Status of this Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as
   Internet-Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/1id-abstracts.html

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html












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Copyright and License Notice

   Copyright (c) 2010 IETF Trust and the persons identified as the
   document authors. All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document. Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document. Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.



Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
      1.1.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Cached Information Extension  . . . . . . . . . . . . . . . . . 4
   4.  Extension Exchange  . . . . . . . . . . . . . . . . . . . . . . 5
      4.1. Reconnaissance  . . . . . . . . . . . . . . . . . . . . . . 5
      4.2. Cached Information  . . . . . . . . . . . . . . . . . . . . 5
   5.  Data Substitution . . . . . . . . . . . . . . . . . . . . . . . 6
      5.1.  Data Substitution Syntax for certificate_chain . . . . . . 6
      5.2.  Data Substitution Syntax for trusted_cas . . . . . . . . . 7
   6.  Security Considerations . . . . . . . . . . . . . . . . . . . . 7
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 8
   8.  Normative References  . . . . . . . . . . . . . . . . . . . . . 8
   Annex A - 64 bit FNV-1 Digest . . . . . . . . . . . . . . . . . . . 9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10


















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1.  Introduction

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

   Significant benefits can be achieved in low bandwidth and high
   latency networks, in particular if the communication channel also has
   a relatively high rate of transmission errors, if a known and
   previously cached server certificate path can be omitted from the TLS
   handshake.

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


1.1.  Terminology

   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.  Cached Information Extension

   A new extension type (cached_information(TBD)) 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 contain "CachedInformation" according to the
   following structure:

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

      struct {
           CachedInformationType type;
           opaque digest_value<0..8>;
      } CachedObject;

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


   The digest_value of a CachedObject MUST either be empty (0 bytes) or
   contain a 64 bit FNV digest (8 bytes) as specified in Annex A. The 64
   bit integer is represented as an 8 byte digest_value in big-endian
   order (with most significant bits in the first byte and least
   significant bits in the last byte).

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

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







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   Other specifications MAY define more CachedInformationType types.

4.  Extension Exchange

4.1. 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.

   A server indicates that it supports cached information in handshakes
   according to section 4.2. by including a cached_information extension
   in its (extended) server hello.

4.2. Cached Information

   Clients MAY specify cached information from previous handshakes by
   including a "cached_information" extension in the (extended) client
   hello, which contains at least one cached object (CachedObject) for
   each present object type (CachedInformationType), as specified in
   section 2. 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
   [RFC4366] value. Clients sending a non-empty cached_information
   extension MUST provide a 64 bit (8 byte) digest_value for each cached
   object.

   Servers that receive an extended client hello containing a
   "cached_information" extension, MAY indicate that they support
   caching of information objects by including an cached_information
   extension in their (extended) server hello.

   A cached_information extension provided in the server hello has the
   following semantics:

     o An empty 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 supports only those CachedInformationType types that are
       identified by each present CachedObject.

     o A CachedObject with an empty digest_value indicates that the
       server supports caching of the specified object type
       (CachedInformationType), but does not specify any digest values
       it will accept.




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     o A present non-empty digest_value indicates that the server will
       honor caching of objects of the specified type that matches the
       present digest value.


5.  Data Substitution

   Following a successful exchange of "cached_information" extensions,
   the server may substitute data objects in the handshake exchange with
   a matching digest_value representing a matching object type. received
   from the client in its client hello.

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

   Each CachedInformationType MUST specify how actual data is replaced
   by a digest in a way that does not violate the defined syntax of
   existing handshake messages. the data exchange syntax for
   certificate_chain(1) and trusted_cas(2) are provided below.

   The server MUST NOT provide more than one digest value as
   substitution for the cached data.

5.1.  Data Substitution Syntax for certificate_chain

   When a digest for an object of type certificate_chain is provided in
   the client hello, the server MAY substitute the cached data with a
   matching digest value received from the client by expanding the
   Certificate handshake message as follows.

   Original handshake message syntax defined in RFC 5246 [RFC5246]:

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

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


   Substitution syntax is defined by expanding the definition of the
   opaque ASN.1Cert structure:

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




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      struct {
          opaque digest_value<0..8>;
      } DigestInfo;


5.2.  Data Substitution Syntax for trusted_cas

   When a digest for an object of type trusted_cas is provided in the
   client hello, the server MAY substitute the cached data with a
   matching digest value received from the client by expanding the
   CertificateRequest handshake message as follows.

   Original handshake message syntax defined in RFC 5246 [RFC5246]:

      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 the definition of the
   opaque DistinguishedName structure:

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

      struct {
          opaque digest_value<0..8>;
      } DigestInfo;


6.  Security Considerations

   The digest algorithm used in this specification is required to have
   reasonable random properties in order to provide reasonably unique
   identifiers. There is no requirement that this digest algorithm must
   have strong collision resistance. A non unique digest may at most
   lead to a failed TLS handshake followed by a new attempt without the
   cached information extension. There are no identified security
   threats that require the selected digest algorithm to have strong
   collision resistance.







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7.  IANA Considerations

   1) Create an entry, cached_information(TBD), in the existing registry
      for ExtensionType (defined in RFC 5246 [RFC5246]).

   2) Establish a registry for TLS CachedInformationType values.  The
      first entries in the registry are certificate_chain(1) and
      trusted_cas(2). TLS CachedInformationType values in the inclusive
      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.  Normative References


   [RFC2119]   S. Bradner, "Key words for use in RFCs to Indicate
               Requirement Levels", BCP 14, RFC 2119, March 1997

   [RFC5226]   T. Narten, H. Alvestrand, "Guidelines for Writing an IANA
               Considerations Section in RFCs", RFC 5226, May 2008

   [RFC5246]   T. Dierks, E. Rescorla, "The Transport Layer Security
               (TLS) Protocol Version 1.2", RFC 5246, August 2008

   [RFC4366]   S. Blake-Wilson, M. Nystrom, D. Hopwood, J. Mikkelsen, T.
               Wright, "Transport Layer Security (TLS) Extensions", RFC
               4366, April 2006

   NOTE: RFC 4366 will be updated by RFC4366bis, currently in IESG
         process.

















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Annex A - 64 bit FNV-1 Digest

   FNV-1 digest algorithm is a non-cryptographic hash function created
   by Glenn Fowler, Landon Curt Noll, and Phong Vo. The FNV digest
   algorithms and sample FNV source code have been released into the
   public domain.

   The FNV-1 digest is generated as follows:

      digest = FNV_offset_basis
      for each octet_of_data to be digested
        digest = digest * FNV_prime
        digest = digest XOR octet_of_data
      return digest

   In the above pseudocode, all variables are unsigned integers. All
   variables, except for octet_of_data, have the same number of bits as
   the FNV digest (64 Bits). The variable, octet_of_data, is an 8 bit
   unsigned integer. Specifically for a 64 bit FNV-1 digest the
   following applies:

     o All variables, except for octet_of_data, are 64-bit unsigned
       integers.

     o The variable, octet_of_data, is an 8 bit unsigned integer.

     o The FNV_offset_basis is the 64-bit FNV offset basis value:
       14695981039346656037.

     o The FNV_prime is the 64-bit FNV prime value: 1099511628211.

     o The multiply function (indicated by the '*' symbol) returns the
       lower 64-bits of the product.

     o The XOR is an 8-bit operation that modifies only the lower 8-bits
       of the digest value.

     o The digest value returned is an 64-bit unsigned integer.













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Authors' Addresses


   Stefan Santesson

   3xA Security AB
   Bjornstorp 744
   247 98 Genarp
   Sweden

   EMail: sts@aaa-sec.com








































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