Internet Engineering Task Force                                M. Badra 
INTERNET DRAFT                                           A. Serhrouchni 
Expires December 2004                                          P. Urien 
                                                           ENST Telecom 
                                                              June 2004 
 
 
                                TLS Express 
                     <draft-badra-tls-express-00.txt> 
    
    
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Copyright Notice 
    
   Copyright (C) The Internet Society (2004).  All Rights Reserved. 
    
Abstract 
    
   This document defines a new extension that may be used to add Pre 
   Shared Key authentication functionality to TLS. It is based on the 
   TLS abbreviated handshake and it provides the ability to share a 
   session key for data encryption. 







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1. Introduction 
    
   [TLSEXT] describes extensions that MAY be used to add functionality 
   to Transport Layer Security (TLS). It provides both generic 
   extension mechanisms for the TLS handshake client and server hellos, 
   and specific extensions using these generic mechanisms.  
    
   In this document, we propose a new extension to add pre shared key 
   functionality to TLS handshake protocol. It is based on [PIMRC] and 
   uses the TLS session resume logic. It provides the client and the 
   server the ability to share a session key for data encryption and to 
   authenticate each other by sending a correct finished message, 
   parties thus prove that they know the correct pre shared key.  
    
1.1. Requirements language 
    
   The key words "MUST", "SHALL", "SHOULD", and "MAY", in this document 
   are to be interpreted as described in RFC-2119. 
    
2. Extension Type 
    
   The TLS extensions [TLSEXT] specify extensions using the following 
   generic mechanism: 
    
       struct { 
           ExtensionType extension_type; 
           opaque extension_data<0.. 2^16-1>; 
          } Extension; 
    
   where "extension_type" identifies the particular extension type, and 
   "extension_data" contains information specific to the particular 
   extension type. 
    
       enum { 
           server_name(0), max_fragment_length(1), 
           client_certificate_url(2), trusted_ca_keys(3), 
           truncated_hmac(4), status_request(5), srp(6), cert_type(7), 
           ticket_identity(8), (65535) 
           } ExtensionType; 
    
   A new value, "ticket_identity(8)", has been added to the enumerated 
   ExtensionType defined in [TLSEXT]. This value is used as the 
   extension number for the extensions in the client hello message. 
   This new extension type will be used for shared key type 
   negotiation. 
    
   The "extension_data" field of the ticket extension SHALL contain: 
    
         opaque ticket_to_enter<1..2^16-1> 
    


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   where ticket_to_enter is the shared key identifier and/or data 
   related to the shared key. 
    
   Note that the secret key MAY be delivered by a trusted third party. 
   In [PIMRC], we gave a method for this topic. By the way, the secret 
   MAY be also issued directly by the server. Kerberos [KERBEROS] is a 
   particular example for this issue. 
    
2.1. Handshake 
    
   In order to indicate the support of the shared key type, the client 
   will include an extension of type "ticket_identity" to the extended 
   client hello message. 
    
   When the server receives an extended client hello containing the 
   "ticket_identity" extension, it checks its ticket_identity's 
   database for a match. If a match is found, the server calculates the 
   finished and waits for the client one.  
    
   If the server understood the client hello extension but does not 
   recognize the ticket identity, it SHOULD send a "decode_error" 
   alert. Alternatively and like in [TLSSRP], if the server wishes to 
   hide the fact that the ticket_identity does not have a match, the 
   server MAY simulate the protocol as if a ticket existed, but then 
   reject the client's finished message with a bad_record_mac alert, as 
   if the shared key was incorrect. 
    
   The handshake exchange is given in the following diagram: 
    
         ClientHello            --------> 
      (ticket_identity)                    ServerHello 
                                           ChangeCipherSpec 
                                <--------  Finished 
         ChangeCipherSpec 
         Finished               --------> 
    
3. Security considerations 
    
   The server MUST stock the shared key in a secure and protected 
   manner in order to prevent attackers from retrieving its value. 
    
4. IANA Considerations 
    
   To be continued. 
    
    
    
    
    
    
    
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5. References 
    
5.1  Normative References 
    
   [TLSEXT]  Blake-Wilson, S., Nystrom, M., Hopwwod, D., Mikkelsen, J.  
             and Wright, T., "Transport Layer Security (TLS)  
             Extensions", RFC 3546, June 2003  
    
   [KERBEROS]Kohl J. and C. Neuman, "The Kerberos Network   
             Authentication Service (V5)", RFC 1510, September 1993. 
    
5.2  Informative References 
    
   [TLSSRP]  Taylor, D., Wu, T., Mavroyanopoulos, N., and Perrin,  
             T., "Using SRP for TLS Authentication", 
             draft-ietf-tls-srp-07.txt, Internet Draft (work in  
             progress), June 2004. 
    
   [PIMRC]   Badra, M., and Serhrouchni, A., "A new secure session   
             exchange key protocol for wireless communications", the 
             14 IEEE Proceedings on Personal, Indoor and Mobile Radio 
             Communications, PIMRC 2003, Volume: 3, 7-10 Sept. 2003,  
             Pages:2765 - 2769. An extracted text could be found at  
             http://www.infres.enst.fr/~badra/pimrc2003.pdf 
    
6. Author's Addresses 
    
   Mohamad Badra 
   ENST 
   46 rue Barrault 
   75634 Paris               Phone: NA 
   France                    Email: Mohamad.Badra@enst.fr 
    
   Ahmed Serhrouchni 
   ENST 
   46 rue Barrault 
   75634 Paris               Phone: NA 
   France                    Email: Ahmed.Serhrouchni@enst.fr 
    
   Pascal Urien 
   ENST 
   46 rue Barrault 
   75634 Paris               Phone: NA 
   France                    Email: Pascal.Urien@enst.fr 
    
    
    
    
    
    
    
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   Internet Society. 
 







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