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Versions: (draft-jiang-dhc-cga-config-dhcpv6) 00 01 02 03 04

Network Working Group                                      Sheng Jiang
Internet Draft                                        Sam(Zhongqi) Xia
Intended status: Standards Track          Huawei Technologies Co., Ltd
Expires: May 06, 2013                                November 05, 2012

  Configuring Cryptographically Generated Addresses (CGA) using DHCPv6
                  draft-ietf-dhc-cga-config-dhcpv6-04


Status of this Memo

   This Internet-Draft is submitted in full conformance with the
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   This Internet-Draft will expire on May 06, 2013.

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   Copyright (c) 2012 IETF Trust and the persons identified as the
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Abstract

   A Cryptographically Generated Address is an IPv6 addresses binding
   with a public/private key pair. However, the current CGA
   specifications are lack of procedures to enable proper management of
   the usage of CGAs. This document analyzes the parameters required for
   the generation of CGA from network configuration and management
   perspective. The configuration procedures of many CGA-relevant
   parameters with existing mechanisms are described in the document.
   Only Sec value has no suitable mechanism to be configured by network
   admin. A new DHCPv6 option is defined accordingly. This document also
   analyses the configuration of the parameters, which are used to
   generate CGAs, using DHCPv6. Although the document does not define
   new DHCPv6 option to carry these parameters for various reasons, the
   configuration procedure is described.

Table of Contents

   1. Introduction ................................................ 3
   2. Terminology ................................................. 3
   3. CGA Configure Process Using DHCPv6 .......................... 4
      3.1. Configuration of the parameters required for the generation
      of CGA ...................................................... 4
      3.2. Host requests CGA Approved to the DHCPv6 server ........ 5
   4. CGA Grant Option ............................................ 7
   5. Security Considerations ..................................... 8
   6. IANA Considerations ......................................... 8
   7. Acknowledgments ............................................. 8
   8. References .................................................. 8
      8.1. Normative References ................................... 8
      8.2. Informative References ................................. 9
   Author's Addresses ............................................ 10














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1. Introduction

   Cryptographically Generated Addresses (CGA, [RFC3972]) provide means
   to verify the ownership of IPv6 addresses without requiring any
   security infrastructure such as a certification authority.

   CGAs were originally designed for SeND [RFC3971] and SeND is
   generally not used in the same environment as a Dynamic Host
   Configure Protocol for IPv6 (DHCPv6) [RFC3315] server. However, after
   CGA has been defined, as an independent security property, many other
   CGA usages have been proposed and defined, such as Site Multihoming
   by IPv6 Intermediation (SHIM6) [RFC5533], Enhanced Route Optimization
   for Mobile IPv6 [RFC4866], also using the CGA for DHCP security
   purpose [I-D.ietf-dhc-secure-dhcpv6], etc. The use of CGAs allows
   identity verification in different protocols. In these scenarios,
   CGAs may be used in DHCPv6-managed networks.

   This document analyses the configuration of the parameters, which are
   used to generate CGAs, from network configuration and management
   perspective. Although the document does not define new DHCPv6 option
   to carry these parameters for various reasons, the configuration
   procedure is described. The procedure works with existing options or
   future define options.

   In current specifications, the network administration can NOT grant
   the use of host-generated CGA addresses on request from the client,
   or reject the CGA on the basis of a too-low sec value. In order to
   fill this gap, a new DHCPv6 option, CGA Grant Option, is defined in
   this document.

   The CGA configuration procedure described in this document can work
   with a generic address registration mechanism. However, even a
   generic address registration mechanism was defined, the CGA-specific
   option, CGA Grant Option, is still needed so that DHCPv6 server can
   indicate hosts the recommended CGA Sec value.

2. 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 RFC2119 [RFC2119].






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3. CGA Configure Process Using DHCPv6

   The CGA specifications [RFC3972] define the procedure to generate a
   CGA. However, it assumes that hosts decide by itself or have been
   preconfigured all CGA relevant parameters. In reality, the network
   management MAY want to assign/enforcement some parameters to hosts;
   the network management MAY also manage the use of CGAs.

   Among the mechanisms in which configuration parameters could be
   pushed to the end hosts and/or CGA related information sent back to a
   central administration, we discuss the stateful configuration
   mechanism based on DCHPv6 in this document. Other mechanisms may also
   provide similar functions, but out of scope.

   In this section, configuration CGA parameters and that a DHCPv6
   server grants the CGA usage are described in details.

3.1. Configuration of the parameters required for the generation of CGA

   Each CGA is associated with a CGA Parameters data structure, which is
   formed by all input parameters [RFC3972] except for Sec value that is
   embedded in the CGA. The CGA associated Parameters used to generate a
   CGA includes:

     - a Public Key,

     - a Subnet Prefix,

     - a 3-bit security parameter, Sec. Additionally, it should be noted
     that the hash algorithm to be used in the generation of the CGA is
     also defined by the Sec value [RFC4982],

     - any Extension Fields that could be used.

     - Note: the modifier and the Collision Count value in the CGA
     Parameter data structure are generated during the CGA generation
     process. They do NOT need to be configured.

   In a DHCPv6 managed network, a host may initiate a request for the
   relevant CGA configuration information needed to the DHCPv6 server.
   The server responds with the configuration information for the host.
   The Option Request Option, defined in Section 22.7 in [RFC3315], can
   be used for host to indicate which options the client requests from
   the server. For response, the requested Option should be included.
   The server MAY also initiatively push these parameters by attaching
   these option in the response messages which are initiated for other
   purposes.


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     - The Public/Private key pair is generated by hosts themselves and
     considered not suitable for network transmission for security
     reasons. The configuration of the client key pair or certificate is
     out of scope.

     - Currently, there are convenient mechanisms for allowing an
     administrator to configure the subnet prefix for a host, by Router
     Advertisement [RFC4861, RFC4862]. However, this does not suitable
     for the DHCP-managed network. To propagate the prefix through DHCP
     interactions, DHCPv6 Prefix Delegation Option [RFC3633] MAY be
     used. However, this option was designed to assign prefix block for
     routers. A new Prefix Assignment Option MAY need to be defined.
     Since alternative approach is existing and there are debates
     whether a new Prefix Assignment Option MAY is necessary, this
     document does not define it.

     - Although the network management MAY want to enforce or configure
     a Sec value to the hosts, it is considered as a very dangerous
     action. A malicious fake server may send out a high Sec value to
     attack clients giving the fact that generation a CGA with a high
     Sec value is very computational intensive. Another risk is that a
     malicious server could propagate a Sec value providing less
     protection than intended by the network administrator, facilitating
     a brute force attack against the hash, or the selection of the
     weakest hash algorithm available for CGA definition. A
     recommendation Sec value is considered as confusion information.
     The receiving host is lack for information to make choose whether
     generates a CGA according to the recommendation or not. Therefore,
     the document does not define a DHCPv6 option to propagate the Sec
     value.

     - Although there is an optional Extension Fields in CGA Parameter
     data structure, there is NO any defined extension fields. If in the
     future, new Extension Fields in CGA Parameter data structure are
     defined, future specification may define correspondent DHCPv6
     options to carry these parameters.

   Upon reception of the CGA relevant parameters from DHCPv6 server, the
   end hosts SHOULD generate addresses compliant with the received
   parameters. If the parameters change, the end hosts SHOULD generate
   new addresses compliant with the parameters propagated.

3.2. Host requests CGA Approved to the DHCPv6 server

   A CGA address is generated by the associated key pair owner, normally
   an end host. However, in a DHCPv6-managed network, hosts should use
   IPv6 global addresses only from a DHCPv6 server. The process


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   described below allows a host, also DHCPv6 client, uses self-
   generated CGAs in a DHCPv6-managed environment, by requesting the
   granting from a DHCPv6 server.

   The client sends a CGA, which is generated by itself, to a DHCPv6
   server, and requests the DHCP server to determine whether the
   generated CGA satisfies the requirements of the network
   configuration, wherein the network configuration comprises a CGA
   security level set by the DHCP; and generates a new CGA if the
   generated CGA does not satisfy the requirements of the network
   configuration.

   - Client initiation behavior

       In details, a DHCPv6 client SHOULD send a DHCPv6 Request message
       to initiate the CGA granting process.

       This DHCPv6 Request message MUST include an Option Request option
       [RFC3315], which requests the CGA Grant Option, defined in
       Section 4 in this document, to indicate the DHCPv6 server
       responses with the address granting decision.

       The client MUST include one or more IA Options, either IA_NA or
       IA_TA, in the Request message. Each IA Option MUST includes one
       or more IA Address Options. CGAs are carried in the IA Address
       Options.

   - Server behavior

       Upon reception of the Request message, the DHCPv6 server SHOULD
       verify whether the client's CGAs satisfy the CGA-related
       configuration parameters of the network. The DHCPv6 server then
       send an acknowledgement, a Reply message, to the client to either
       grant the use of the CGA or decline the requested CGA. The
       CGA_Grant field SHOULD be set following the rule, defined in
       Section 4 in this document. When the requested CGA is declined,
       the DHCPv6 server MAY also recommend a Sec value to the client
       using the CGA Grant option in the DHCPv6 Reply message.

       In the meantime, the DHCPv6 server MAY log the requested CGA
       addresses. This information MAY later be used by other network
       functions, such as ACL.

   - Client receiving behavior

      Upon reception of the acknowledgement from server, the client can
      legally use the granted CGAs. The client SHOULD silently drop any


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      message that has the CGA_Grant field set any other value, but F0x,
      or 00x~07x. If the server declines the requested CGA, the client
      MAY generate a new CGA with the recommended Sec value. If the
      server replies with CGA-relevant parameters, the client MAY
      generate a new CGA accordingly.

4. CGA Grant Option

   DHCPv6 CGA Grant Option is used to indicate the DHCPv6 client whether
   the requested address is granted or not. In the decline case, a
   recommended Sec value MAY be sent, too.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       OPTION_ADDR_GRANT       |       option-len              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   CGA Grant   |
   +-+-+-+-+-+-+-+-+

       option-code

         OPTION_ADDR_GRANT (TBA1).

       option-len

         1.

       CGA_Grant

         In the DHCPv6 reply message, the CGA_Grant field sets F0x to
         indicate that the requested CGA is granted; it sets 00x to
         indicate that the requested Address is declined without any
         recommended Sec value. It sets 01x~07x to indicate that
         requested Address is declined and the recommended Sec value
         (value from 1~7).

   Note: On receiving the CGA Grant Option with reject information and a
   recommended Sec value, the client MAY generate a new CGA with the
   recommended Sec value. If choosing not use the recommended Sec value,
   the client MAY take the risk that it is not able to use full network
   capabilities. The network may consider the hosts that use CGAs with
   lower Sec values as unsecure users and decline some or all network
   services.





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5. Security Considerations

   The mechanisms based on DHCPv6 are all vulnerable to attacks to the
   DHCP client. Proper use of DHCPv6 autoconfiguration facilities
   [RFC3315], such as AUTH option or Secure DHCP
   [I-D.ietf-dhc-secure-dhcpv6] can prevent these threats, provided that
   a configuration token is known to both the client and the server.

   IF a DHCPv6 server rejected a client CGA based on a certain Sec
   value, it SHOULD NOT suggest a new Sec value either equal or lower
   than the Sec value that has been rejected.

   Note that, as expected, it is not possible to provide secure
   configuration of CGA without a previous configuration of security
   information at the client (either a trust anchor, or a DHCPv6
   configuration token, etc.). However, considering that the values of
   these elements could be shared by the hosts in the network segment,
   these security elements can be configured more easily in the end
   hosts than its addresses.

6. IANA Considerations

   This document defines two new DHCPv6 [RFC3315] options, which must be
   assigned Option Type values within the option numbering space for
   DHCPv6 messages:

   The DHCPv6 CGA Grant Option, OPTION_ADDR_GRANT (TBA1), described in
   Section 4.

7. Acknowledgments

   The authors would like to thank Marcelo Bagnulo Braun and Alberto
   Garcia-Martinez for been involved in the early requirement
   identification. Valuable comments from Bernie Volz, Ted Lemon, John
   Jason Brzozowski, Dujuan Gu and other DHC WG members are appreciated.

8. References

8.1. Normative References

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

   [RFC3315] R. Droms, Ed., "Dynamic Host Configure Protocol for IPv6",
             RFC3315, July 2003.




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   [RFC3633] O. Troan and R. Droms, "IPv6 Prefix Options for Dynamic
             Host Configuration Protocol (DHCP) version 6", RFC 3633,
             December 2003.

   [RFC3971] J. Arkko, J. Kempf, B. Zill and P. Nikander, "SEcure
             Neighbor Discovery (SEND) ", RFC 3971, March 2005.

   [RFC3972] T. Aura, "Cryptographically Generated Address", RFC3972,
             March 2005.

   [RFC4861] T. Narten, et al., "Neighbor Discovery for IP version 6
             (IPv6)", RFC 4861, September 2007.

   [RFC4862] S. Thomson, T. Narten and T. Jinmei, "IPv6 Stateless
             Address Autoconfiguration", RFC4862, September 2007.

   [RFC4866] J. Arkko, C. Vogt and W. Haddad, "Enhanced Route
             Optimization for Mobile IPv6", RFC4866, May 2007.

   [RFC4982] M. Bagnulo, "Support for Multiple Hash Algorithms in
             Cryptographically Generated Addresses (CGAs) ", RFC4982,
             July 2007.

   [RFC5533] E. Nordmark and M. Bagnulo, "Shim6: Level 3 Multihoming
             Shim Protocol for IPv6" FRC 5533, June 2009.

8.2. Informative References

   [I-D.ietf-dhc-secure-dhcpv6]
             S. Jiang and S. Shen, "Secure DHCPv6 Using CGAs", draft-
             ietf-dhc-secure-dhcpv6 (work in progress), Septerber, 2012.

















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Author's Addresses

   Sheng Jiang
   Huawei Technologies Co., Ltd
   Q14 Huawei Campus, 156 BeiQi Road,
   ZhongGuan Cun, Hai-Dian District, Beijing 100085
   P.R. China
   Email: jiangsheng@huawei.com


   Sam(Zhongqi) Xia
   Huawei Technologies Co., Ltd
   Q14 Huawei Campus, 156 BeiQi Road,
   ZhongGuan Cun, Hai-Dian District, Beijing 100085
   P.R. China
   Email: xiazhongqi@huawei.com
































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