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Versions: 00 01 02 03 04 05 06 07 RFC 6704

softwire                                                        D. Miles
Internet-Draft                                            Alcatel-Lucent
Intended status: Standards Track                                  W. Dec
Expires: September 11, 2011                                Cisco Systems
                                                              J. Bristow
                                                     Swisscom Schweiz AG
                                                             R. Maglione
                                                          Telecom Italia
                                                          March 10, 2011


                    Forcerenew Nonce Authentication
                   draft-ietf-dhc-forcerenew-nonce-01

Abstract

   DHCP Forcerenew allows for the reconfiguration of a single host by
   forcing the DHCP client into a Renew state on a trigger from the DHCP
   server.  In Forcerenew Nonce Authentication the server exchanges a
   nonce with the client on the initial DHCP ACK that is used for
   subsequent validation of a Forcerenew message.

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 September 11, 2011.

Copyright Notice

   Copyright (c) 2011 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



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   carefully, as they describe your rights and restrictions with respect
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   include Simplified BSD License text as described in Section 4.e of
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   it for publication as an RFC or to translate it into languages other
   than English.


































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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Requirements Language  . . . . . . . . . . . . . . . . . . . .  4
   3.  Message authentication . . . . . . . . . . . . . . . . . . . .  4
     3.1.  Forcerenew Nonce Authentication  . . . . . . . . . . . . .  4
       3.1.1.  Forcerenew Nonce Protocol Capability Option  . . . . .  5
       3.1.2.  Forcerenew Nonce Protocol  . . . . . . . . . . . . . .  7
       3.1.3.  Server considerations for Forcerenew Nonce
               Authentication . . . . . . . . . . . . . . . . . . . .  8
       3.1.4.  Client considerations for Forcerenew Nonce
               Authentication . . . . . . . . . . . . . . . . . . . .  9
   4.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10
   5.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 10
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 10
     6.1.  Protocol vulnerabilities . . . . . . . . . . . . . . . . . 10
   7.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
     7.1.  Normative References . . . . . . . . . . . . . . . . . . . 11
     7.2.  Informative References . . . . . . . . . . . . . . . . . . 11
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11































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1.  Introduction

   The DHCP Reconfigure Extension defined in [RFC3203] is a useful
   mechanism allowing dynamic reconfiguration of a single host triggered
   by the DHCP server.  Its application is currently limited by a
   requirement that FORCERENEW message is always authenticated using
   procedures as described in [RFC3118].  Authentication for DHCP
   [RFC3118] is mandatory for Forcerenew, however as it is currently
   defined [RFC3118] requires distribution of constant token or shared-
   secret out-of-band to DHCP clients.  The mandatory authentication was
   originally motivated by a legitimate security concern whereby in some
   network environments a FORCERENEW message can be spoofed.  However,
   in some networks native security mechanisms already provide
   sufficient protection against spoofing of DHCP traffic.  An example
   of such network is a DSL Forum TR-101 [TR-101] compliant access
   network.  In such environments the mandatory coupling between
   FORCERENEW and DHCP Authentication [RFC3118] can be relaxed.  This
   document defines extensions to Authentication for DHCP(v4) Messages
   [RFC3118] to create a new authentication protocol for DHCPv4
   Forcerenew [RFC3203] messages; this method does not require out-of-
   band key distribution to DHCP clients.  The Forcerenew Nonce is
   exchanged between server and client on initial DHCP ACK and is used
   for verification of any subsequent Forcerenew message.


2.  Requirements Language

   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 [RFC2119].


3.  Message authentication

   The FORCERENEW message must be authenticated using either [RFC3118]
   or the proposed Forcerenew Nonce Authentication protocol.

3.1.  Forcerenew Nonce Authentication

   The Forcerenew nonce authentication protocol provides protection
   against misconfiguration of a client caused by a Forcerenew message
   sent by a malicious DHCP server.  In this protocol, a DHCP server
   sends a Forcerenew nonce to the client in the initial exchange of
   DHCP messages.  The client records the Forcerenew nonce for use in
   authenticating subsequent Forcerenew messages from that server.  The
   server then includes an HMAC computed from the Forcerenew nonce in
   subsequent Forcerenew messages.




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   Both the Forcerenew nonce sent from the server to the client and the
   HMAC in subsequent Forcerenew messages are carried as the
   Authentication information in a DHCP Authentication option.  The
   format of the Authentication information is defined in the following
   section.

   The Forcerenew nonce protocol is used (initiated by the server) only
   if the client and server are not using any other authentication
   protocol and the client and server have negotiated to use the
   Forcerenew Nonce Authentication protocol.

3.1.1.  Forcerenew Nonce Protocol Capability Option

   A DHCP client indicates DHCP Forcerenew Nonce Protocol capability by
   including a FORCERENEW_NONCE_CAPABLE(<TBD>) option in DHCP Discover
   and Request messages sent to the server.

   A DHCP server that does not support Forcerenew Nonce Protocol
   authentication should ignore the FORCERENEW_NONCE_CAPABLE(<TBD>)
   option.  A DHCP server indicates DHCP Forcerenew Nonce Protocol
   preference by including a FORCERENEW_NONCE_CAPABLE(<TBD>) option in
   any DHCP Offer messages sent to the client.

   A DHCP client MUST NOT send DHCP messages with authentication options
   where the protocol value is Forcerenew Nonce Authentication(<TBD>).

   The FORCERENEW_NONCE_CAPABLE option is a zero length option with code
   of <TDB> and format as follows:

             Code   Len
            +-----+-----+
            | TBD |  0  |
            +-----+-----+

   The client would indicate that it supports the functionality by
   inserting the FORCERENEW_NONCE_CAPABLE option in the DHCP Discover
   and Request messages.  If the server supports Forcerenew nonce
   authentication and is configured to require Forcerenew nonce
   authentication, it will insert the FORCERENEW_NONCE_CAPABLE option in
   the DHCP Offer message.

                     Server          Client          Server
                 (not selected)                    (selected)

                       v               v               v
                       |               |               |
                       |     Begins initialization     |
                       |               |               |



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                       | _____________/|\____________  |
                       |/DHCPDISCOVER  | DHCPDISCOVER \|
                       | w/Forcerenew- | w/Forcerenew- |
                       | Nonce-Capable | Nonce-Capable |
                       |               |               |
                   Determines          |          Determines
                  configuration        |         configuration
                       |               |               |
                       |\              |              /|
                       | \__________   |    _________/ |
                       |  DHCPOFFER \  |   /DHCPOFFER  |
                       |w/Forcerenew \ |  /w/Forcerenew|
                       |Nonce-Capable \| /Nonce-Capable|
                       |               |               |
                       |       Collects replies        |
                       |               |               |
                       |     Selects configuration     |
                       |               |               |
                       | _____________/|\____________  |
                       |/ DHCPREQUEST  |  DHCPREQUEST\ |
                       | w/Forcerenew- | w/Forcerenew- |
                       | Nonce-Capable | Nonce-Capable |
                       |               |               |
                       |               |     Commits configuration
                       |               |               |
                       |               |Creates 128-bit Forcerenew Nonce
                       |               |               |
                       |               | _____________/|
                       |               |/ DHCPACK      |
                       |               | w/Auth-Proto= |
                       |               | Forcerenew-   |
                       |               |        Nonce  |
                       |               |               |
                       |Client stores Forcerenew Nonce |
                       |               |               |
                       |    Initialization complete    |
                       |               |               |
                       .               .               .
                       .               .               .
                       |               |               |
                       |          Forcerenew           |
                       |               | _____________/|
                       |               |/ DHCPFORCE    |
                       |               | w/Auth-Proto= |
                       |               | Forcerenew-   |
                       |               |   Digest(HMAC)|
                       |               |               |
                       | Client checks HMAC digest     |



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                       | using stored Forcerenew Nonce |
                       |               |               |
                       |               |\____________  |
                       |               |  DHCPREQUEST\ |
                       |               | w/Forcerenew- |
                       |               | Nonce-Capable |
                       |               |               |
                       |               |     Commits configuration
                       |               |               |
                       |               |Creates 128-bit Forcerenew Nonce
                       |               |               |
                       |               | _____________/|
                       |               |/ DHCPACK      |
                       |               | w/Auth-Proto= |
                       |               |   Forcerenew- |
                       |               |         Nonce |
                       |               |               |
                       |               |               |
                       |               |               |
                       .               .               .
                       .               .               .
                       |               |               |
                       |      Graceful shutdown        |
                       |               |               |
                       |               |\ ____________ |
                       |               | DHCPRELEASE  \|
                       |               |               |
                       |               |        Discards lease
                       |               |               |
                       v               v               v


3.1.2.  Forcerenew Nonce Protocol

   [RFC3118] defined an extensible DHCPv4 authentication option which
   supports multiple protocols.  The Forcerenew Nonce Protocol makes use
   of the DHCP authentication option defined in [RFC3118] re-using the
   option format.

   The following fields are set in an DHCP authentication option for the
   Forcerenew Nonce Authentication Protocol:

        protocol <TBD (IANA)>








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        algorithm 1

        RDM 0

   The format of the Authentication information for the Forcerenew Nonce
   Authentication Protocol is:

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |     Type      |                 Value (128 bits)              |
       +-+-+-+-+-+-+-+-+                                               |
       .                                                               .
       .                                                               .
       .                                               +-+-+-+-+-+-+-+-+
       |                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type Type of data in Value field carried in this option:

        1 Forcerenew Nonce value (used in ACK message)

        2 HMAC-MD5 digest of the message (FORCERENEW message)

   Value  Data as defined by field

3.1.3.  Server considerations for Forcerenew Nonce Authentication

   The use of Forcerenew Nonce Protocol is dependent on the client
   indicating its capability through the FORCERENEW_NONCE_CAPABLE(<TBD>)
   DHCP option in any DHCP Discover or Request messages.  The DHCP
   Discovery or Request message from the client MUST contain the
   FORCERENEW_NONCE_CAPABLE(<TBD>) option if the Forcerenew Nonce
   Protocol is to be used by the server.  The absence of the
   FORCERENEW_NONCE_CAPABLE(<TBD>) option indicates to the server that
   the Forcerenew Nonce Authentication protocol is not supported and
   thus the server MUST NOT include a Forcerenew Nonce Protocol
   Authentication option in the DHCP Ack.

   The server indicates its support of the Forcerenew Nonce Protocol
   authentication by including the DHCP FORCERENEW_NONCE_CAPABLE(<TBDP>)
   option in the DHCP Offer message.  The server SHOULD NOT include this
   option unless the client has indicated its capability in a DHCP
   Discovery message .  The presence of the
   FORCERENEW_NONCE_CAPABLE(<TDB>) option in the DHCP offer may be used
   by clients to prefer Forcerenew nonce Protocol authentication-capable
   DHCP servers over those servers which do not support such capability.




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   The server selects a Forcerenew nonce for a client only during
   Request/Ack message exchange.  The server records the Forcerenew
   nonce and transmits that nonce to the client in an Authentication
   option in the DHCP Ack message.

   The Forcerenew nonce is 128 bits long, and MUST be a
   cryptographically strong random or pseudo-random number that cannot
   easily be predicted.  The nonce is imbedded as a 128-bit value of the
   Authentication information where type is set to 1 (Forcerenew nonce
   Value).

   To provide authentication for a Forcerenew message, the server
   selects a replay detection value according to the RDM selected by the
   server, and computes an HMAC-MD5 of the Forcerenew message using the
   Forcerenew nonce for the client.  The server computes the HMAC-MD5
   over the entire DHCP Forcerenew message, including the Authentication
   option; the HMAC-MD5 field in the Authentication option is set to
   zero for the HMAC-MD5 computation.  The server includes the HMAC-MD5
   in the authentication information field in an Authentication option
   included in the Forcerenew message sent to the client with type set
   to 2 (HMAC-MD5 digest).

3.1.4.  Client considerations for Forcerenew Nonce Authentication

   The client MUST indicate Forcerenew nonce Capability by including the
   FORCERENEW_NONCE_CAPABLE(<TBD>) DHCP option (Section 2.1.1) in all
   DHCP Discover and Request messages.  DHCP servers that support
   Forcerenew nonce Protocol authentication MUST include the DHCP
   Forcerenew Nonce protocol authentication option in DHCP Offers with
   type set to zero(0), allowing the client to use this capability in
   selecting DHCP servers should multiple Offers arrive.

   A DHCP server has indicates its support through the inclusion of the
   FORCERENEW_NONCE_CAPABLE(<TBD>) option in the DHCP Offer.  The client
   MUST validate the DHCP Ack message contains a Forcerenew Nonce in a
   DHCP authentication option.  If the server has indicated capability
   for Forcerenew Nonce Protocol authentication in the DHCP Offer and a
   subsequent Ack omits a valid DHCP authentication option for the
   Forcerenew Nonce Protocol, the client MUST send a DHCP Decline
   message and return to the DHCP Init state.

   The client will receive a Forcerenew Nonce from the server in the
   initial DHCP Ack message from the server.  The client records the
   Forcerenew Nonce for use in authenticating subsequent Forcerenew
   messages.

   To authenticate a Forcerenew message, the client computes an HMAC-MD5
   over the DHCP Forcerenew message, using the Forcerenew Nonce received



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   from the server.  If this computed HMAC-MD5 matches the value in the
   Authentication option, the client accepts the Forcerenew message.


4.  Acknowledgements

   Comments are solicited and should be addressed to the DHC WG mailing
   list (dhcwg@ietf.org) and/or the authors.  This contribution is based
   on work by Vitali Vinokour.  Major sections of this draft use
   modified text from [RFC3315].  The authors wish to thank Ted Lemon
   and Bernie Volz for their support.


5.  IANA Considerations

   This document requests IANA to allocate an option code for the newly
   defined DHCP option FORCERENEW_NONCE_CAPABALE as described in the
   text.

   This document requests IANA to allocate a DHCP Authentication
   Option(90) protocol number be assigned for Forcerenew Nonce
   Authentication, per [RFC3118].

   This document requests IANA to create a new namespace associated with
   the Forcerenew Nonce Authentication protocol: algorithm, per
   [RFC3118].


6.  Security Considerations

   As in some network environments FORCERENEW can be used to snoop and
   spoof traffic, the FORCERENEW message MUST be authenticated using the
   procedures as described in [RFC3118] or this proposal.  In this
   proposal any party able intercept the nonce exchange could
   impersonate a server and thus offers no protection from man-in-the-
   middle attacks.  FORCERENEW messages failing the authentication
   should be silently discarded by the client.

6.1.  Protocol vulnerabilities

   The mechanism described in this document is vulnerable to a denial of
   service attack through flooding a client with bogus FORCERENEW
   messages.  The calculations involved in authenticating the bogus
   FORECERENEW messages may overwhelm the device on which the client is
   running.

   The mechanism described provides protection against the use of a
   FORCERENEW message by a malicious DHCP server to mount a denial of



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   service or man-in-the-middle attack on a client.  This protocol can
   be compromised by an attacker that can intercept the initial message
   in which the DHCP server sends the nonce to the client.


7.  References

7.1.  Normative References

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

   [RFC3118]  Droms, R. and W. Arbaugh, "Authentication for DHCP
              Messages", RFC 3118, June 2001.

   [RFC3203]  T'Joens, Y., Hublet, C., and P. De Schrijver, "DHCP
              reconfigure extension", RFC 3203, December 2001.

7.2.  Informative References

   [RFC3315]  Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
              and M. Carney, "Dynamic Host Configuration Protocol for
              IPv6 (DHCPv6)", RFC 3315, July 2003.

   [TR-101]   Cohen et al, "Architecture & Transport: "Migration to
              Ethernet Based DSL Aggregation, DSL Forum TR-101", 2005.


Authors' Addresses

   David Miles
   Alcatel-Lucent
   L3 / 215 Spring St
   Melbourne, Victoria 3000,
   Australia

   Phone: +61 3 9664 3308
   Fax:
   Email: david.miles@alcatel-lucent.com
   URI:











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   Wojciech Dec
   Cisco Systems
   Haarlerbergpark Haarlerbergweg 13-19
   Amsterdam, NOORD-HOLLAND  1101 CH
   Netherlands

   Phone:
   Fax:
   Email: wdec@cisco.com
   URI:


   James Bristow
   Swisscom Schweiz AG
   Zentweg 9
   Bern, 3050,
   Switzerland

   Phone:
   Fax:
   Email: James.Bristow@swisscom.com
   URI:


   Roberta Maglione
   Telecom Italia
   Via Reiss Romoli 274
   Torino  10148
   Italy

   Phone:
   Email: roberta.maglione@telecomitalia.it



















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