path: root/doc/protocol/draft-badra-tls-password-ext-00.txt

Internet Engineering Task Force                                M. Badra 
INTERNET DRAFT                                         LIMOS Laboratory 
April 19, 2007                                    Expires: October 2007 
    
    
              Password Extension for TLS Client Authentication 
                    <draft-badra-tls-password-ext-00.txt> 
    
    
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Copyright Notice 
    
   Copyright (C) The IETF Trust (2007).  
    
Abstract 
    
   This document specifies a new TLS extension and a new TLS message 
   providing TLS client authentication using passwords. It provides 
   client credential protection. 
    






 
 
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1 Introduction 
    
   This document defines a new extension and a new TLS message to the 
   TLS protocol to enable TLS client authentication using passwords. It 
   provides client credential protection. 
    
1.2 Requirements language and Terminologies 
    
   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 [KEYWORDS]. 
    
2. Password Extension 
    
   In order to negotiate the use of client password-based 
   authentication, clients MAY include an extension of type "password" 
   in the extended client hello. The "extension_data" field of this 
   extension SHALL be empty. The extension_type field is to be assigned 
   by IANA. 
    
   For servers aware of the password extension but not wishing to use 
   it, it will gracefully revert to an ordinary TLS handshake or stop 
   the negotiation. 
    
   Servers that receive an extended hello containing a "password" 
   extension MAY agree to authenticate the client using passwords by 
   including an extension of type "password", with empty 
   "extension_data", in the extended server hello. The 
   CertificateRequest payload is omitted from the server response. 
    
   Clients return a response along with their credentials by sending a 
   "EncryptedPassword" message immediately after the 
   "ClientKeyExchange" message. The encrypted password message is sent 
   symmetrically encrypted with the key client_write_key and the cipher 
   algorithm selected by the server in the ServerHello.cipher_suite. 
   The Certificate and CertificateVerify payloads are omitted from the 
   client response. 
    
2.1. Encrypted Password 
    
   When this message will be sent: 
    
   The client MUST send this message immediately after the client key 
   exchange message. 
    
    
    
    

 
 
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   Structure of this message: 
    
        struct { 
           uint16 length; 
           select (CipherSpec.cipher_type) { 
             case stream:  
                   stream-ciphered struct { 
                      opaque fresh_random<16..2^16-1>; 
                      opaque login<1..2^16-1>; 
                      opaque password<1..2^16-1>; 
                  }; 
             case block: 
                   block-ciphered struct { 
                      opaque IV[CipherSpec.block_length]; 
                      opaque login<1..2^16-1>; 
                      opaque password<1..2^16-1>; 
                      uint8 padding[EncryptedPassword.padding_length]; 
                      uint8 padding_length; 
                  };    
            } EncryptedPassword; 
    
   fresh_random  
     A vector contains at least 16 bytes. 
    
   length 
     The length (in bytes) of the EncryptedPassword structure. 
    
   padding 
     Padding that is added to force the length of the EncryptedPassword  
     structure to be an integral multiple of the block cipher's block  
     length. The padding MAY be any length up to 255 bytes, as long as  
     it results in the EncryptedPassword.length being an integral  
     multiple of the block length. Lengths longer than necessary might  
     be desirable to frustrate attacks on a protocol that are based on  
     analysis of the lengths of exchanged messages. Each uint8 in the  
     padding data vector MUST be filled with the padding length value.  
     The receiver MUST check this padding and SHOULD use the  
     bad_record_mac alert to indicate padding errors. 
    
   padding_length 
     The padding length MUST be such that the total size of the 
     EncryptedPassword structure is a multiple of the cipher's block  
     length. Legal values range from zero to 255, inclusive. This 
     length specifies the length of the padding field exclusive of the 
     padding_length field itself. 
    


 
 
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   BulkCipherAlgorithm.null (e.g. TLS_RSA_WITH_NULL_MD5 and 
   RSA_WITH_NULL_SHA) MUST NOT be negotiated when password extension is 
   deployed, as it provides no more protection than an unsecured 
   connection. 
    
   Implementations of this document MUST ensure that all policies being 
   applied on the PSK encoding (section 5 of [PSK]) are applied on the 
   password encoding as well. 
    
   Editor note: is it more secure to don't send the password on the 
   wire and instead of that, mix it with the premaster secret, and use 
   the result as an input for the key derivation function to implicitly 
   authenticate the client? 
    
   Upon receipt of this message, the server symmetrically decrypts the 
   EncryptedPassword using the same key as the client to retrieve the 
   username and the password in clear text. The server then checks its 
   database for a match. If a match is found, the server sends its 
   change cipher spec message and proceeds directly to finished 
   message. If no match is found, the server MUST send a fatal alert, 
   results in the immediate termination of the connection. 
    
   If the server does not recognize the login, it MAY respond with an 
   "unknown_login" alert message. Alternatively, if the server wishes 
   to hide the fact that the login was not known, it MAY continue the 
   protocol as if the login existed but the key was incorrect: that is, 
   respond with a "decrypt_error" alert. 
    
        Client                                               Server 
        ------                                               ------ 
     
        ClientHello             --------> 
                                                        ServerHello 
                                                       Certificate* 
                                                 ServerKeyExchange* 
                                <--------           ServerHelloDone 
        ClientKeyExchange 
        EncryptedPassword 
        ChangeCipherSpec 
        Finished                --------> 
                                                   ChangeCipherSpec 
                                <--------                  Finished 
        Application Data                           Application Data 
        Attribute Value Pairs                 Attribute Value Pairs 
        Type Length Value       <=======>         Type Length Value 
    
3. Security Considerations 
    

 
 
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   The security considerations described throughout [TLS], [DTLS], and 
   [TLS1.1] apply here as well. 
    
4. IANA Considerations 
    
   This document defines a new TLS extension "password", assigned the 
   value TBD from the TLS ExtensionType registry defined in [TLSEXT]. 
    
   This document also defines a new TLS alert message, 
   unknown_login(TBD). 
    
   This document defines a new handshake message, encrypted password, 
   whose value is to be allocated from the TLS HandshakeType registry 
   defined in [TLS]. 
    
5. References 
    
5.1. Normative References 
    
   [TLS]      Dierks, T. and C. Allen, "The TLS Protocol Version 1.0",  
              RFC 2246, January 1999. 
    
   [TLSExt]   Blake-Wilson, S., et. al., "Transport Layer Security TLS)  
              Extensions", RFC 4346, April 2006. 
    
   [KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate 
              Requirement Levels", RFC 2119, March 1997. 
    
   [PSK]      Eronen, P. (Ed.) and H. Tschofenig (Ed.), "Pre-Shared Key  
              Ciphersuites for Transport Layer Security (TLS)",  
              RFC 4279, December 2005. 
    
   [TLSCAM]   Moriai, S., Kato, A., Kanda M., "Addition of Camellia  
              Cipher Suites to Transport Layer Security (TLS)",  
              RFC 4132, July 2005. 
    
   [TLSAES]   Chown, P., "Advanced Encryption Standard (AES)  
              Ciphersuites for Transport Layer Security (TLS)",  
              RFC 3268, June 2002. 
    
   [TLSECC]   Blake-Wilson, S., Bolyard, N., Gupta, V., Hawk, C.,  
              Moeller, B., "Elliptic Curve Cryptography (ECC) Cipher  
              Suites for Transport Layer Security (TLS)", RFC 4492, May  
              2006 
    
   [TLSCTR]   Modadugu, N. and E. Rescorla, "AES Counter Mode Cipher  
              Suites for TLS and DTLS", draft-ietf-tls-ctr-01.txt (work  
              in progress), June 2006. 

 
 
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5.2. Informative References 
    
   [KERB]     Medvinsky, A. and M. Hur, "Addition of Kerberos Cipher 
              Suites to Transport Layer Security (TLS)", RFC 2712, 
              October 1999.  
    
Author's Addresses 
    
   Mohamad Badra 
   LIMOS Laboratory - UMR (6158), CNRS 
   France             Email: badra@isima.fr 
    
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