Network Working Group Sheng Jiang Internet Draft Sam(Zhongqi) Xia Intended status: Standards Track Huawei Technologies Co., Ltd Expires: February 24, 2011 August 24, 2010 Configuring Cryptographically Generated Addresses (CGA) using DHCPv6 draft-jiang-dhc-cga-config-dhcpv6-01.txt 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 Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on February 24, 2011. Copyright Notice Copyright (c) 2010 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 carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Jiang & Xia Expires February 24, 2011 [Page 1]
Internet-Draft draft-jiang-dhc-cga-config-dhcpv6-01.txt August 2010 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 CGA generation. Administrators should be able to configure parameters used to generate CGA. The Dynamic Host Configuration Protocol for IPv6 (DHCPv6), which enables network management to dynamically configure hosts, can be used in the CGA configuration. This document defines the process using DHCPv6 to configure CGA in detail, include configuration CGA parameters and that a DHCPv6 server grants the CGA usage. Two new DHCPv6 options are defined accordingly. Table of Contents 1. Introduction................................................3 2. Terminology.................................................3 3. CGA Configure Process Using DHCPv6...........................3 3.1. Configuration of the parameters required for the generation of CGA......................................................4 3.2. Node requests CGA Approved to the DHCPv6 server..........5 4. DHCPv6 CGA Sec Option........................................6 5. DHCPv6 Address Grant Option..................................7 6. Security Considerations......................................7 7. IANA Considerations.........................................8 8. Acknowledgments.............................................8 9. References..................................................8 9.1. Normative References....................................8 9.2. Informative References..................................9 Author's Addresses.............................................9 Jiang & Xia Expires February 24, 2011 [Page 2]
Internet-Draft draft-jiang-dhc-cga-config-dhcpv6-01.txt August 2010 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. The use of CGAs allows identity verification in different protocols, such as SEure Neighbor Discovery (SEND, [RFC3971]), Enhanced Route Optimization for MIPv6 [RFC4866] or Site Multihoming by IPv6 Intermediation (SHIM6 [RFC5533]). However, as [I-D.ietf-csi-dhcpv6-cga-ps] analyses, in the current specifications, there is a lack of procedures to enable proper management of CGA generation, in particular, in the configuration of the parameters that define the security properties of the addresses. Administrators should be able to configure parameters used to generate CGA. The Dynamic Host Configuration Protocol for IPv6 (DHCPv6), which enables network management to dynamically configure hosts, can be used in the CGA configuration. For example, DHCPv6 server should be able to assign certain level of CGA Sec value or other relevant parameters to CGA address owner. This draft provides detailed solutions for CGA configuration. Two existing DHCPv6 options are re-used. Two new DHCPv6 options, CGA Sec Option and Address Grant Option, are also defined in this document. 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]. 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, network management MAY want to assign/enforcement some parameters to hosts. 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. Jiang & Xia Expires February 24, 2011 [Page 3]
Internet-Draft draft-jiang-dhc-cga-config-dhcpv6-01.txt August 2010 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. A node may initiate a request for the relevant CGA configuration information needed to the DHCPv6 server. The server responds with the configuration information for the node. The Option Request Option, defined in Section 22.7 in [RFC3315], can be used for node 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. 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 Jiang & Xia Expires February 24, 2011 [Page 4]
Internet-Draft draft-jiang-dhc-cga-config-dhcpv6-01.txt August 2010 whether a new Prefix Assignment Option MAY is necessary, this document does not define it. A new DHCPv6 CGA Sec Option is defined in Section 4. Although there is an optional Extension Fields in CGA Parameter data structure, there is NO any defined extension fields. Future specification may define more options to carry CGA-related configuration 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. Node 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 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, which requests Address Grant Option, defined in Section 5 in this document, to indicate the DHCPv6 server responses with the address granting decision. The Addr_Grant field in the embedded Address Grant Option should be set 0. The client MUST include one or more IA Options, either IA_NA or IA_TA, in the Request message. Each IA Option MUST include one or more IA Address Options. CGAs are carried in the IA Address Options. Server behavior Jiang & Xia Expires February 24, 2011 [Page 5]
Internet-Draft draft-jiang-dhc-cga-config-dhcpv6-01.txt August 2010 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 to indicate that the node must generate a new CGA with the correct CGA-related configuration parameters of the network. The Addr_Grant field sets 1 indicating that the requested address is granted; The Addr_Grant field sets 2 indicating that the requested address is declined, defined in Section 5 in this document. When the requested CGA is declined, the DHCPv6 server may attach CGA- relevant parameters in the Reply message to indicate the client generates a new CGA accordingly. 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. If the server declines the requested CGA, the client MUST generate a new CGA. If the server replies with CGA-relevant parameters, the client SHOULD generate a new CGA accordingly. 4. DHCPv6 CGA Sec Option DHCPv6 CGA Sec Option is used to carry a Sec value, the parameters associated with CGA generation on a client. After receiving the CGA Sec Option, the client SHOULD generate a CGA using a Sec value that is not lower than the option indicated. 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_CGA_SEC | option-len | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | CGA SEC | +-+-+-+-+-+-+-+-+ option-code OPTION_CGA_SEC (TBA1). option-len 1. CGA SEC a digit between 0 and 7, the SEC level. Jiang & Xia Expires February 24, 2011 [Page 6]
Internet-Draft draft-jiang-dhc-cga-config-dhcpv6-01.txt August 2010 Note: On receiving the CGA Sec Option, the client MAY choose to generate a CGA using a lower sec value. It MAY cause that the client is not able to use full network capabilities. 5. DHCPv6 Address Grant Option DHCPv6 Address Grant Option is used to indicate the DHCPv6 client whether the requested address is granted or not. 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Addr Grant | +-+-+-+-+-+-+-+-+ option-code OPTION_ADDR_GRANT (TBA2). option-len 1. Addr Grant The Addr_Grant field sets 0 when a client requests granting from server. It sets 1 indicating that the requested Address is granted; it sets 2 indicating that the requested Address is declined. 6. Security Considerations The mechanisms based on DHCPv6 are all vulnerable to attacks to the DHCP client, such as request for CGA generation with a high Sec value. 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. 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, a DHCPv6 configuration token...). However, considering that the values of these elements could be shared by the nodes in the network segment, these security elements can be configured more easily in the end nodes than its addresses. Regarding to the configuration of the Sec parameter, one risk is that a malicious node could propagate a Sec value providing less protection than intended by the network administrator, facilitating a Jiang & Xia Expires February 24, 2011 [Page 7]
Internet-Draft draft-jiang-dhc-cga-config-dhcpv6-01.txt August 2010 brute force attack against the hash, or the selection of the weakest hash algorithm available for CGA definition. However, even in the worst case, if the hash algorithm cannot be inverted, the expected number of iterations required for a brute force attack is O(2^59) in order to find a CGA Parameters data structure that matches a given CGA. Another risk is the use of a Sec, higher than intended by the administrator, which would require a large number of resources of the client to compute the modifier, requiring a long time before the device can communicate. This can be considered a kind of DOS attack. A variation of this attack is the propagation of different Sec values. This kind of attack may be prevented by protected DHCPv6 interactions. 7. 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 Sec Option (TBA1), described in Section 4. The DHCPv6 Address Grant Option (TBA2), described in Section 5. 8. Acknowledgments The authors would like to thank Marcelo Bagnulo Braun and Alberto Garcia-Martinez from Universidad Carlos III de Madrid for been involved in the early requirement identification. Valuable comments from Bernie Volz, Cisco and Dujuan Gu, Huawei are appreciated. 9. References 9.1. 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. [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. Jiang & Xia Expires February 24, 2011 [Page 8]
Internet-Draft draft-jiang-dhc-cga-config-dhcpv6-01.txt August 2010 [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. 9.2. Informative References [I-D.ietf-csi-dhcpv6-cga-ps] S. Jiang, S. Shen and T. Chown, "DHCPv6 and CGA Interaction: Problem Statement", draft-ietf-csi-dhcpv6-cga-ps (work in progress), June, 2010. [I-D.ietf-dhc-secure-dhcpv6] S. Jiang and S. Shen, "Secure DHCPv6 Using CGAs", draft- ietf-dhc-secure-dhcpv6 (work in progress), June 2010. Author's Addresses Sheng Jiang Huawei Technologies Co., Ltd Huawei Building, No.3 Xinxi Rd., Shang-Di Information Industry Base, Hai-Dian District, Beijing 100085 P.R. China Email: shengjiang@huawei.com Sam(Zhongqi) Xia Huawei Technologies Co., Ltd Huawei Building, No.3 Xinxi Rd., Shang-Di Information Industry Base, Hai-Dian District, Beijing 100085 P.R. China Email: xiazhongqi@huawei.com Jiang & Xia Expires February 24, 2011 [Page 9]