MIP4 Working Group S. Lai Internet-Draft H. Deng Expires: December 22, 2006 Hitachi (China) June 20, 2006 Problem of Replay Protection Using Sequence Number in Proxy Mobile IPv4 draft-lai-mip4-proxy-sequence-problem-00.txt Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. 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." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on December 22, 2006. Copyright Notice Copyright (C) The Internet Society (2006). Abstract The document presents the problems of replay protection using sequence number in proxy Mobile IPv4 solution. The sequence number cannot prevent registration message from replay attack. Lai & Deng Expires December 22, 2006 [Page 1] Internet-Draft Problem with Sequence Number June 2006 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Problem of Using Sequence Number for Replay Protection . . . . 4 4. Security Considerations . . . . . . . . . . . . . . . . . . . . 5 5. References . . . . . . . . . . . . . . . . . . . . . . . . . . 5 5.1. Normative References . . . . . . . . . . . . . . . . . . . 5 5.2. Informative References . . . . . . . . . . . . . . . . . . 5 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 6 Intellectual Property and Copyright Statements . . . . . . . . . . 7 Lai & Deng Expires December 22, 2006 [Page 2] Internet-Draft Problem with Sequence Number June 2006 1. Introduction Proxy Mobile IPv4 is a helpful solution which to provide mobility for mobile device with no MIP4 function [RFC3344]. The main idea of proxy Mobile IP is that an Mobile IPv4 entity, defined as Mobility Proxy Agent in this document, offers mobility service for a mobile device by initiating the MIP4 registration procedure on behalf of mobile device. In Proxy MIP4 solution [Proxy-MIP4], a new registration doesn't have sequence number and re-registration containes sequence number assigned by Home Agent(HA). Hence HA can distinguish a new registration from stale registrations generated by previous Mobility Proxy Agent. However, such sequence number cannot prevent registration message from replay attack. An attacker can intercept previous new registration and replay it to HA. Then HA will be deceived by the replayed registration and bind a wrong care-of address for mobile device. 2. Terminology The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14, [RFC2119]. The following new terminology and abbreviations are introduced in this document and all other general mobility related terms as defined in Mobile IPv4 specification [RFC3543]. Mobile Station (MS) Any IPv4 node that has the ability to physically access or roam across different networks. The Mobile Station does not necessarily have the Mobile IPv4 protocol stack. Mobility Proxy Agent (MPA) The Mobile IPv4 entity that offers proxy mobility service for a Mobile Station by performing registration function on the host's behalf. It may be the Access Point, Base Station, Mobile Terminal, Access Router, or Access Gateway. Lai & Deng Expires December 22, 2006 [Page 3] Internet-Draft Problem with Sequence Number June 2006 3. Problem of Using Sequence Number for Replay Protection MS MPA-1 MPA-2 HA |MS @ MPA-1 | | | x-----------x | | | |Reg Request| | | |(no sequence number) | 1)| o---------------------->| | | | | 2)| | | o MS @ MPA-1 | | | | | | |Reg Reply | | | |sequence=X | 3)| |<----------------------o | | | | |MS moved to MPA-2 | | x-----------------------x | | | |Reg Request| | | |(no sequence number) 4)| | o---------->| | | | | 5)| | | o MS @ MPA-2 | | | | | | |Reg Reply | | | |sequence=X+1 6)| | |<----------o | | | | Figure 1: Sequence Maintenance in Proxy Mobile IPv4 The using of sequence number in Proxy MIP4 [Proxy-MIP4] is illustrated in figure 1. When MPA is attached to MPA1, MPA1 will send Registration Request with no sequence number on MS's behalf(step1). HA assigns a sequence number 'X' in the Registration Reply. Subsequent registration requests from MPA1 contains the sequence number. After MS moves and connects with MPA2, MPA2 will send proxy Registration Request with no sequence number to HA(step4). And HA returns back a sequence number 'X+1' in the Registration Reply. Subsequent registration requests from MPA2 contains the sequence number 'X+1'. By checking the sequence number in the registration message, HA knows which registration is new and ignore stale registrations. If a malicious node intercepts previous Registration Request from MPA1, the malicious node can replay the intercepted message to HA Lai & Deng Expires December 22, 2006 [Page 4] Internet-Draft Problem with Sequence Number June 2006 after MS connecting with MPA2. In this case, HA will be cheated that it receives a new Registration Request from MPA1 and hence change the care-of address of MS to IP address of MPA1 even though MS is connected with MPA2. Therefore only sequence number cannot prevent Registration Request from Replay Attack. When a malicious node intercepts previous registrations and replays it to home agent, home agent will have a wrong binding for MS. Even if timestamp is used as sequence number, the problem still cannot be addressed. Unlike in base Mobile IPv4 in which Registration Request is generated by MS, it is MPA that generates Registration Request message. Unless that the machine time in two MPAs are exactly synchronized, Home Agent doesn't know the sequence of these registrations from different MPAs. And HA doesn't know whether a registration message is a replayed message or a valid one. 4. Security Considerations The security problem when using sequence number for anti-replay purpose can be addressed by later solutions. 5. References 5.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC3344] Perkins, C., "IP Mobility Support for IPv4", RFC 3344, August 2002. [RFC3543] Glass, S. and M. Chandra, "Registration Revocation in Mobile IPv4", RFC 3543, August 2003. 5.2. Informative References [Proxy-MIP4] Leung, K., Dommety, G., and P. Yegani, "Mobility Management using Proxy Mobile IPv4", February 2006, . Lai & Deng Expires December 22, 2006 [Page 5] Internet-Draft Problem with Sequence Number June 2006 Authors' Addresses Shouwen Lai Hitachi (China) Beijing Fortune Bldg. 1701 5 Dong San Huan Bei-Lu Chao Yang District Beijing 100004 China Email: swlai@hitachi.cn Hui Deng Hitachi (China) Beijing Fortune Bldg. 1701 5 Dong San Huan Bei-Lu Chao Yang District Beijing 100004 China Email: hdeng@hitachi.cn Lai & Deng Expires December 22, 2006 [Page 6] Internet-Draft Problem with Sequence Number June 2006 Intellectual Property Statement The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org. Disclaimer of Validity This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Copyright Statement Copyright (C) The Internet Society (2006). 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. Lai & Deng Expires December 22, 2006 [Page 7]