path: root/doc/protocol/draft-ietf-netconf-tls-02.txt

NETCONF Working Group                                     Mohamad Badra 
Internet Draft                                         LIMOS Laboratory 
Intended status: Standards Track                           May 27, 2008 
Expires: November 2008 
                                    
 
                                      
                NETCONF over Transport Layer Security (TLS) 
                       draft-ietf-netconf-tls-02.txt 


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   This Internet-Draft will expire on November 27, 2008. 

Copyright Notice 

   Copyright (C) The IETF Trust (2008). 

Abstract 

   The Network Configuration Protocol (NETCONF) provides mechanisms to 
   install, manipulate, and delete the configuration of network devices.  
   This document describes how to use the Transport Layer Protocol (TLS) 
   to secure NETCONF exchanges. 


 
 
 
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Table of Contents 

    
   1. Introduction...................................................3 
      1.1. Conventions used in this document.........................3 
   2. NETCONF over TLS...............................................3 
      2.1. Connection Initiation.....................................3 
      2.2. Connection Closure........................................4 
   3. Endpoint Authentication and Identification.....................4 
      3.1. Server Identity...........................................5 
      3.2. Client Identity...........................................6 
      3.3. Password-Based Authentication.............................6 
   4. Cipher Suite Requirements......................................7 
   5. Security Considerations........................................7 
   6. IANA Considerations............................................7 
   7. Acknowledgments................................................8 
   A. Appendix - Test Vectors for the PSK Derivation Function........9 
   B. Appendix - Enabling Third Party Authentication using Passwords10 
      B.1. Working Group discussion at the 71st IETF meeting........12 
   Normative References.............................................13 
   Authors' Addresses...............................................14 
   Intellectual Property and Copyright Statements...................14 
    
























 
 
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1. Introduction 
   The NETCONF protocol [RFC4741] defines a simple mechanism through 
   which a network device can be managed.  NETCONF is connection-
   oriented, requiring a persistent connection between peers.  This 
   connection must provide reliable, sequenced data delivery, integrity 
   and confidentiality and peers authentication.  This document 
   describes how to use TLS [RFC4346] to secure NETCONF connections. 

   Throughout this document, the terms "client" and "server" are used to 
   refer to the two ends of the TLS connection.  The client actively 
   opens the TLS connection, and the server passively listens for the 
   incoming TLS connection.  The terms "manager" and "agent" are used to 
   refer to the two ends of the NETCONF protocol session.  The manager 
   issues NETCONF remote procedure call (RPC) commands, and the agent 
   replies to those commands.  When NETCONF is run over TLS using the 
   mapping defined in this document, the client is always the manager, 
   and the server is always the agent. 

1.1. Conventions used in this document 

   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]. 

2. NETCONF over TLS 

   Since TLS is application protocol-independent, NETCONF can operate on 
   top of the TLS protocol transparently.  This document defines how 
   NETCONF can be used within a Transport Layer Security (TLS) session. 

2.1. Connection Initiation 

   The peer acting as the NETCONF manager MUST also act as the TLS 
   client.  It MUST connect to the server that passively listens for the 
   incoming TLS connection on the IANA-to-be-assigned TCP port <TBA>.  
   It MUST therefore send the TLS ClientHello to begin the TLS 
   handshake.  Once the TLS handshake has been finished, the client and 
   the server MAY then send their NETCONF exchanges.  In particular, the 
   client will send complete XML documents to the server containing 
   <rpc> elements, and the server will respond with complete XML 
   documents containing <rpc-reply> elements.  The client MAY indicate 
   interest in receiving event notifications from a NETCONF server by 
   creating a subscription to receive event notifications [I-D.ietf--
   netconf-notification], in which the NETCONF server replies to 
   indicate whether the subscription request was successful and, if it 
   was successful, begins sending the event notifications to the NETCONF 
   client as the events occur within the system.  All these elements are 
 
 
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   encapsulated into TLS records of type "application data".  These 
   records are protected using the TLS material keys. 

   Current NETCONF messages don't include a message's length.  This 
   document uses consequently the same delimiter sequence defined in 
   [RFC4742] and therefore the special character sequence, ]]>]]>, to 
   delimit XML documents. 

2.2. Connection Closure 

   Either NETCONF peer MAY stop the NETCONF connection at any time and 
   therefore notify the other NETCONF peer that no more data on this 
   channel will be sent and that any data received after a closure 
   request will be ignored.  This MAY happen when no data is received 
   from a connection for a long time, where the application decides what 
   "long" means. 

   TLS has the ability for secure connection closure using the Alert 
   protocol.  When the NETCONF peer closes the NETCONF connection, it 
   MUST send a TLS close_notify alert before closing the TCP connection.  
   Any data received after a closure alert is ignored. 

   Unless a fatal error has occurred, each party is required to send a 
   close_notify alert before closing the write side of the connection 
   [RFC4346].  The other party MUST respond with a close_notify alert of 
   its own and close down the connection immediately, discarding any 
   pending writes.  It is not required for the initiator of the close to 
   wait for the responding close_notify alert before closing the read 
   side of the connection. 

3. Endpoint Authentication and Identification 

   NETCONF requires that its transport provide mutual authentication of 
   client and server, so cipher suites that are anonymous or which only 
   authenticate the server to the client MUST NOT be used with NETCONF.  
   This document specifies how to use TLS with endpoint authentication, 
   which can be based on either preshared keys [RFC4279] or public key 
   certificates [RFC4346].  Some cipher suites (e.g. 
   TLS_RSA_PSK_WITH_AES_128_CBC_SHA) use both.  Section 3.1 describes 
   how the client authenticates the server if public key certificates 
   are provided by the server, section 3.2 describes how the server 
   authenticates the client if public key certificates are provided by 
   the client, and section 3.3 describes how the client and server 
   mutually authenticate one another using a password. 



 
 
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3.1. Server Identity 

   During the TLS negotiation, the client MUST carefully examine the 
   certificate presented by the server to determine if it meets their 
   expectations.  Particularly, the client MUST check its understanding 
   of the server hostname against the server's identity as presented in 
   the server Certificate message, in order to prevent man-in-the-middle 
   attacks. 

   Matching is performed according to these rules [RFC4642]: 

      - The client MUST use the server hostname it used to open the 
        connection (or the hostname specified in TLS "server_name" 
        extension [RFC4366]) as the value to compare against the server 
        name as expressed in the server certificate.  The client MUST 
        NOT use any form of the server hostname derived from an 
        insecure remote source (e.g., insecure DNS lookup).  CNAME 
        canonicalization is not done. 

      - If a subjectAltName extension of type dNSName is present in the 
        certificate, it MUST be used as the source of the server's 
        identity. 

      - Matching is case-insensitive. 

      - A "*" wildcard character MAY be used as the left-most name 
        component in the certificate.  For example, *.example.com would 
        match a.example.com, foo.example.com, etc., but would not match 
        example.com. 

      - If the certificate contains multiple names (e.g., more than one 
        dNSName field), then a match with any one of the fields is 
        considered acceptable. 

   If the match fails, the client MUST either ask for explicit user 
   confirmation or terminate the connection and indicate the server's 
   identity is suspect. 

   Additionally, clients MUST verify the binding between the identity of 
   the servers to which they connect and the public keys presented by 
   those servers.  Clients SHOULD implement the algorithm in Section 6 
   of [RFC5280] for general certificate validation, but MAY supplement 
   that algorithm with other validation methods that achieve equivalent 
   levels of verification (such as comparing the server certificate 
   against a local store of already-verified certificates and identity 
   bindings). 

 
 
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   If the client has external information as to the expected identity of 
   the server, the hostname check MAY be omitted. 

3.2. Client Identity 

   Typically, the server has no external knowledge of what the client's 
   identity ought to be and so checks (other than that the client has a 
   certificate chain rooted in an appropriate CA) are not possible.  If 
   a server has such knowledge (typically from some source external to 
   NETCONF or TLS) it MUST check the identity as described above. 

3.3. Password-Based Authentication 

   [RFC4279] supports authentication based on pre-shared keys (PSKs).  
   These pre-shared keys are symmetric keys, shared in advance among the 
   communicating parties. 

   The PSK can be generated in many ways and its length is variable.  
   Implementation of this document MAY rely on [RFC4279] to enable 
   password based user authentication.  In this case, the password is 
   used to generate the PSK.  It is RECOMMENDED that implementations 
   that allow the administrator to manually configure the password also 
   provide functionality for generating a new random password, taking 
   [RFC4086] into account. 

   This document generates the PSK from the password as follow: 

    PSK = SHA-1(SHA-1(psk_identity + "Key Pad for Netconf" + password) +  
                psk_identity_hint)  

   Where + means concatenation.  

   The label "Key Pad for Netconf" is an ASCII string.  

   The psk_identity_hint is initially defined in section 5.1 of 
   [RFC4279].  The psk_identity_hint can do double duty and also provide 
   a form of server authentication in the case where the user has the 
   same password on a number of NETCONF servers.  If a hint is provided, 
   the psk_identity_hint is encoded in the same way as in [RFC4279] and 
   should be a string representation of the name of the server 
   recognizable to the administrator or his software.  In the case where 
   the user types a server name to connect to, it should be that string.  
   If the string the user enters differs from the one returned as 
   psk_identity_hint, the software could display the server's name and 
   ask the user to confirm.  For automated scripts, the names could be 
   expected to match.  It is highly recommended that implementations set 

 
 
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   the psk_identity_hint to the DNS name of the NETCONF server (i.e., 
   the TLS server). 

   It is RECOMMENDED that users choose different passwords for the 
   different servers they manage. 

      Note 1: The NETCONF over TLS implementation need not store the 
      password in clear text, but rather can store the value of the 
      inner SHA-1 (SHA-1(SHA-1(password + psk_identity + "Key Pad for 
      Netconf") + psk_identity_hint)), which could not be used as a 
      password equivalent for applications other than NETCONF.  Deriving 
      the PSK from a password is not secure.  This construction is used 
      because it is anticipated that people will do it anyway. 

      Note 2: [RFC4279] defines some conformance requirements for the 
      PSK, for the PSK identity encoding and for the identity hint. The 
      same requirements apply here as well; in particular on the 
      password.  Moreover, the management interface by which the 
      password is provided MUST accept ASCII strings of at least 64 
      octets and MUST NOT add a null terminator before using them as 
      shared secrets.  It MUST also accept a HEX encoding of the 
      password.  The management interface MAY accept other encodings if 
      the algorithm for translating the encoding to a binary string is 
      specified. 

4. Cipher Suite Requirements 

   A compliant implementation of the protocol specified in this document 
   MUST implement the cipher suite TLS_DHE_PSK_WITH_AES_128_CBC_SHA and 
   MAY implement any TLS cipher suite that provides mutual 
   authentication.  

5. Security Considerations 

   The security considerations described throughout [RFC4346] and 
   [RFC4279] apply here as well. 

   As with all schemes involving shared keys and passwords, special care 
   should be taken to protect the shared values and passwords as well as 
   to limit their exposure over time.  Alternatively, using certificates 
   would provide better protection. 

6. IANA Considerations 

   IANA is requested to assign a TCP port number that will be the 
   default port for NETCONF over TLS sessions as defined in this 
   document. 
 
 
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   IANA has assigned port <TBA> for this purpose. 

7. Acknowledgments 

   A significant amount of the text in Section 3.1 was lifted from 
   [RFC4642]. 

   The author would like to acknowledge David Harrington, Miao Fuyou, 
   Eric Rescorla, Juergen Schoenwaelder, Simon Josefsson, Olivier 
   Coupelon and the NETCONF mailing list members for their comments on 
   the document.  The author appreciates also Bert Wijnen, Mehmet Ersue 
   and Dan Romascanu for their efforts on issues resolving discussion, 
   and Charlie Kaufman for the thorough review of this document and for 
   the helpful comments on the password-based authentication. 

































 
 
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A. Appendix - Test Vectors for the PSK Derivation Function 

   The test vectors for the PSK derivation function in this document 
   have been cross-verified by two independent implementations.  An 
   implementation that concurs with the results provided in this 
   document should be interoperable with other similar implementations. 

         password = password 
         psk_identity = psk_identity 
         psk_identity_hint = psk_identity_hint 

         The inner SHA-1 value (in hex): 

         inner := SHA-1(password + psk_identity + "Key Pad for Netconf") 
               == SHA-1("psk_identityKey Pad for Netconfpassword") 
               => 6d6eeb6a b8d0466b 45245d07 47d86726 b41b868c 

         The outer SHA-1 value (in hex): 

         outer := SHA-1(inner + psk_identity_hint) 
               => 88f3824b 3e5659f5 2d00e959 bacab954 b6540344 


























 
 
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B. Appendix - Enabling Third Party Authentication using Passwords 

   During the 71st IETF meeting, several proposals have been proposed to 
   enable third party authentication that could be used in combination 
   with existing user authentication databases such as RADIUS. They are 
   listed below. More details on those proposals may be found at 
   https://www3.ietf.org/proceedings/08mar/slides/netconf-1/netconf-
   1.htm and 
   http://www.psg.com/lists/netconf/netconf.2008/msg00125.html. 

   We summarize them as following: 

   1. Defining <user-login> RPC: 
      -------------------------- 

     This option relies on JUNOS mechanism to enable an authentication 
     function via third parties. It consists of establishing a TLS with 
     no manager authentication, leaving the <request-login> RPC as the 
     only valid RPC.  Anything else is an error. 

     Once the TLS session is established, the agent MUST authenticate 
     the manager by emitting the following <rpc> tag element:  

         <rpc-reply message-id="101" 
            xmlns="urn:ietf:params:xml:ns:netconf:base:1.0"> 
              <challenge>Password:</challenge> 
         </rpc-reply> 

       In which the manager MUST reply with the following: 

         <rpc> 
            <request-login> 
               <challenge-response>password</challenge-response> 
            </request-login> 
         </rpc> 

     The rules to handle this were pretty simple: 

        - The <request-login> RPC could only be performed if the session 
          wasn't authenticated. 

        - No other RPCs could be performed if the session wasn't  
          authenticated. 

        - The transport protocol can authenticate the session  
          (internally). 

 
 
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     Pros and cons: 

     o   is simple to do. But 

     o   might raise questions from the security ADs; NETCONF assumes  
         the authentication is part of the transport not NETCONF. 

     o   only works for plaintext passwords (SASL PLAIN). 

   2. Enhancing TLS:  
      -------------- 

     The second option consists of extending TLS so the manager 
     authentication becomes part of TLS. This extension, detailed in 
     http://tools.ietf.org/id/draft-badra-tls-password-ext-01.txt, 
     defines a new extension and a new TLS message to the TLS protocol 
     to enable TLS client authentication using passwords. The extension 
     is used to convey the manager login, whereas the new message is 
     defined and sent by the manager to prove its knowledge of the 
     password. 

     Steps during the TLS negotiation: 

         - The manager adds such an extension to its TLS ClientHello. 

         - If the agent agrees on using this extension, it will notify  
           the manager and replies with its certificate and/or its  
           authenticated public key. 

         - The manager generates a premaster secret and encrypts it  
           using the agent public key. 

         - The manager then computes the session key using the premaster  
           secret and encrypts, among others, its password with the  
           computed key. 

         - The agent decrypts the premaster secret and computes the same  
           key to decrypt the password. 

         - The agent checks with a database (or AAA infrastructures) to  
           verify the password and then to authenticate the manager. 

     Pros and cons 

     o   is simple to do. But 
 
 
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     o   It is indeed not easy to convince TLS WG to add password  
         authentication extension to TLS. 

   3. Running BEEP over TLS:  
      ---------------------- 

     It looks complex for a solution, requires that all implementations 
     do actually support BEEP. 

   4. Extending NETCONF with a message to start TLS:  
      ---------------------------------------------- 

     This option consists of extending NETCONF with a new message to 
     start the TLS negotiation and to perform an authentication 
     mechanism based on RFC4422 (SASL) or on any similar protocol. 

       Pros and cons 

       o   simple to do. But 

       o   might raise questions from the security ADs; NETCONF assumes  
           the authentication is part of the transport not NETCONF.  
           Moreover, it adds complexity related to the use of SASL  
           PLAIN. 

   5. Enable SSH (RFC4742 and TLS (as defined through this document:  
      -------------------------------------------------------------- 

     Since SSH already defines a password-based authentication and 
     because this protocol MUST be implemented as a security protocol 
     for NETCONF, users can rely on SSH for password authentication, and 
     on TLS for authentication using PSK or certificates. This means the 
     agent SHOULD passively listen for the incoming SSH (respectively 
     TLS) connection on port 830 (respectively port <TBA-by-IANA>). 

       Pros and cons 

       o   simple to do. 

       o   already specified by RFC4742 and by the current document.  

B.1. Working Group discussion at the 71st IETF meeting 

   Some of the options have been found as not practical in the WG 
   session during 71st meeting. 

   Options #2 and #3 have not been supported in the WG session.  
 
 
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   Option #1 and # 4 seems to be against the security design for 
   NETCONF. Whether #5 or other options can be accepted by the WG 
   members needs to be discussed on the mailing list. 

Normative References 

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

   [RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S., 
             Housley, R., and W. Polk, "Internet X.509 Public Key 
             Infrastructure Certificate and Certificate Revocation List 
             (CRL) Profile", RFC 5280, May 2008. 

   [RFC4086] Eastlake, D., 3rd, Schiller, J., and S. Crocker, 
             "Randomness Requirements for Security", BCP 106, RFC 4086, 
             June 2005. 

   [RFC4279] Eronen, P. and H. Tschofenig., "Pre-Shared Key Ciphersuites 
             for Transport Layer Security (TLS)", RFC 4279, December 
             2005. 

   [RFC4346] Dierks, T. and E. Rescorla, "The Transport Layer Security 
             (TLS) Protocol 1.1", RFC 4346, April 2006. 

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

   [RFC4642] Murchison, K., Vinocur, J., Newman, C., "Using Transport 
             Layer Security (TLS) with Network News Transfer Protocol 
             (NNTP)", RFC 4642, October 2006 

   [RFC4741] Enns, R., "NETCONF Configuration Protocol", RFC 4741, 
             December 2006. 

   [RFC4742] Wasserman, M. and T. Goddard, "Using the NETCONF 
             Configuration Protocol over Secure Shell (SSH)", RFC 4742, 
             December 2006. 

   [I-D.ietf-netconf-notification]      
             Chisholm, S. and H. Trevino, "NETCONF Event Notifications", 
             draft-ietf-netconf-notification-12.txt, (work in progress), 
             February 2008. 



 
 
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Authors' Addresses 

   Mohamad Badra 
   LIMOS Laboratory - UMR6158, CNRS 
   France 
       
   Email: badra@isima.fr 

Contributors 

   Ibrahim Hajjeh 
   INEOVATION 
   France 
       
   Email: hajjeh@ineovation.com 

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   THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 
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Copyright Statement 

   Copyright (C) The IETF Trust (2008). 

   This document is subject to the rights, licenses and restrictions 
   contained in BCP 78, and except as set forth therein, the authors 
   retain all their rights. 

Acknowledgment 

   Funding for the RFC Editor function is currently provided by the 
   Internet Society. 

 






























 
 
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