Mobile IP Working Group Charles E. Perkins INTERNET DRAFT Nokia Research Center 10 July 2001 Pat R. Calhoun Sun Microsystems Laboratories AAA Registration Keys for Mobile IP draft-ietf-mobileip-aaa-key-07.txt Status of This Memo This document is a submission by the mobile-ip Working Group of the Internet Engineering Task Force (IETF). Comments should be submitted to the mobile-ip@sunroof.eng.sun.com mailing list. Distribution of this memo is unlimited. This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. 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. Abstract AAA servers, such as RADIUS and DIAMETER, are in use within the Internet today to provide authentication and authorization services for dial-up computers. Mobile IP requires strong authentication between the mobile node and its home agent. When the mobile node shares a security association with its home AAA server, however, it is possible to use that security association to create derivative security associations between the mobile node and its home agent, and again between the mobile node and the foreign agent currently offering connectivity to the mobile node. This document specifies extensions to the Mobile IP Registration Reply packet that can be used to create such security information at the mobile node. Perkins, Calhoun Expires 10 Janueary 2002 [Page 1]
Internet Draft AAA Keys for Mobile IP 10 July 2001 1. Introduction AAA servers, such as RADIUS [12] and DIAMETER [3], are in use within the Internet today to provide authentication and authorization services for dial-up computers. Such services are likely to be equally valuable for mobile nodes using Mobile IP when the nodes are attempting to connect to foreign domains with AAA servers. Mobile IP [10] requires strong authentication between the mobile node and its home agent. When the mobile node shares a security association with its home AAA server, however, it is possible to use that security association to create derivative security associations between the mobile node and its home agent, and again between the mobile node and the foreign agent currently offering connectivity to the mobile node. This document specifies extensions to the Mobile IP Registration messages that can be used to create those security associations at the mobile node. AAA servers typically use the Network Access Identifier (NAI) [1] to uniquely identify the mobile node; the mobile node's home address is not always necessary to provide that function. Thus, it is possible for a mobile node to authenticate itself, and be authorized for connection to the foreign domain, without having any home address. However, for Mobile IP to work, the mobile node is required to have a security association with its home agent. When the Mobile IP Registration Reply packet is authenticated by the MN-AAA Authentication Extension [2], the mobile node can verify that the keys contained in the extensions were produced by the AAA server, and thus may be reliably used to create security associations with the home agent, or alternatively with the foreign agent. The protocol and messages in this document are intended to facilitate the following operations which may occur between the mobile node, AAA server, home agent, and foreign agent. 1. When a mobile node travels away from home, it may not have a security association with its home agent, perhaps because it does not yet have a home address. 2. If the mobile node does not have a Mobility Security Association with the foreign agent, it MUST include an MN-FA Key Request extension. 3. Similarly, if the mobile node does not have a Mobility Security Association with the home agent, it MUST add an MN-HA Key Request extension. 4. If one or more Key Request extensions were added, the MN-AAA Authentication extension is added to the Registration Request. Perkins, Calhoun Expires 10 Janueary 2002 [Page 2]
Internet Draft AAA Keys for Mobile IP 10 July 2001 5. At the time the information within the MN-AAA Authentication extension is verified by the AAA server, the AAA server also generates Key Material for the keys requested by the mobile node, and causes insertion of the Key Material fields along with the Registration Reply. 6. The respective AAA keys are distributed to the Home and Foreign Agent via the AAA protocol. 7. If the Reply passes authentication and contains the Unsolicited MN-HA Key Material From AAA extension (see section 5), the mobile node generates the key using the Key Material provided, according to its security association with the AAA. The resulting key is used to establish the mobile node's security association with its home agent, and is used to authenticate the MN-HA authentication extension. 8. Similarly, if the Reply passes authentication and contains the Unsolicited MN-FA Key Material From AAA extension (see section 4), the mobile node generates the key using the Key Material provided, according to its security association with the AAA. The resulting key is used to establish the mobile node's security association with its new foreign agent, and is used to compute the authentication data used in the MN-FA authentication extension. Any registration reply containing the Unsolicited MN-HA Key Material From AAA extension MUST also contain a subsequent Mobile Home Authentication Extension, created using the generated MN-HA key. Similarly, a reply containing the Unsolicited MN-FA Key Material From AAA extension MUST also contain a subsequent Mobile Foreign Authentication Extension, created using the the MN-FA key. 2. Dynamic Security Associations Mobility Security Associations between Mobile IP entities (mobile nodes, home agents, foreign agents) contain both the necessary cryptographic key information, and a way to identify the cryptographic algorithm which uses the key to produce the authentication information typically included in the Mobile Home Authentication extension or the Mobile Foreign Authentication extension. In order for the mobile node to make use of key information sent to it by the AAA server, the mobile node also has to be able to select the appropriate cryptographic algorithm that uses the key to produce the authentication. The following table contains the supported algorithm identifiers. Perkins, Calhoun Expires 10 Janueary 2002 [Page 3]
Internet Draft AAA Keys for Mobile IP 10 July 2001 Algorithm Identifier Name Reference --------------------- ------------------ ------------ 1 MD5/prefix+suffix RFC 2002 [10] 2 HMAC MD5 RFC 2104 [5] 3 SHA-1 FIPS 180-1 [9] New algorithms will be allocated as indicated by practical experience using the extensions defined in this document. Dynamic Mobility Security Associations shared between mobile nodes and home agents also requires a replay protection method. The following table contains the supported replay methods. Replay Method Name Reference -------------- ------------ -------------- 1 None RFC 2002 [10] 2 Timestamps RFC 2002 [10] 3 Nonces RFC 2002 [10] 3. Key Material Creation and Derivation This section contains the procedures followed in the creation of the Key Material by AAA servers, and the key derivation procedures used by mobile nodes. Note that the AAA servers will also make use of the derivation procedures to deliver the keys via the AAA protocol. The example that follows makes use of MD5 in prefix+suffix mode, whose support is mandatory in Mobile IP [10]. Other cryptographic functions, such as those listed in 2 MAY also be used. 1. The AAA server identifies the mobile node's via a ``node-address''. If the Home Address field of the Registration Request is zero (0), the Mobile Node's NAI is used instead. 2. The AAA server generates a random [4] value of at least 64 bits. 3. The AAA server inserts the random value into the Key extension in the ``Key Material'' field. 4. The mobile node calculates key = MD5(AAA-key | Key Material | node-address | AAA-key) Perkins, Calhoun Expires 10 Janueary 2002 [Page 4]
Internet Draft AAA Keys for Mobile IP 10 July 2001 5. The mobile node creates the dynamic security association, using the key, and the other relevant information in the Key Extension. Perkins, Calhoun Expires 10 Janueary 2002 [Page 5]
Internet Draft AAA Keys for Mobile IP 10 July 2001 4. Unsolicited MN-FA Key Material From AAA Subtype 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Lifetime | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | AAA SPI | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | FA SPI | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Algorithm Identifier | Key Material ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1: The Unsolicited MN-FA Key Material From AAA Subtype-Specific Data lifetime This field indicates the duration of time (in seconds) for which the MN-FA key is valid. AAA SPI A 32-bit opaque value, indicating the SPI that the mobile node must use to determine the algorithm to use for establishing the FA security information. FA SPI A 32-bit opaque value, which the mobile node MUST use to index all the necessary information established for the FA security information after it is decoded. Algorithm Identifier This field indicates the algorithm to be used for future computations of the MN-FA Authentication Extension (see section 2) Key Material A random [4] value of at least 64 bits. The Unsolicited MN-FA Key Material From AAA extension, shown in figure 1, uses subtype 7 of the Generalized MN-FA Key Reply Extension [11]. The Key Material is added by the home domain AAA server (AAAH) for use by the mobile node in creating the MN-FA key, which is used to secure future Mobile IP registrations with the same foreign agent. The Unsolicited MN-FA Key Material From AAA extension MUST appear in the Registration Reply before the MN-FA Authentication extension. Perkins, Calhoun Expires 10 Janueary 2002 [Page 6]
Internet Draft AAA Keys for Mobile IP 10 July 2001 Once the mobile node creates the FA Security Information, by using the algorithm indexed by the AAA SPI, it stores the FA Security Information indexed by the FA SPI in its list of Mobile Security Associations. If the foreign agent receives a Registration Reply that does not have a Unsolicited MN-FA Key Material From AAA extension, and thus does not have a way to establish a Mobility Security Association with the mobile node, the foreign agent MAY change the Code value of the Registration Reply to MISSING_MN_FA (see section 8), effectively causing the registration to fail. Perkins, Calhoun Expires 10 Janueary 2002 [Page 7]
Internet Draft AAA Keys for Mobile IP 10 July 2001 5. Unsolicited MN-HA Key Material From AAA Subtype The Unsolicited MN-HA Key Material From AAA is subtype 1 of the Generalized MN-HA Key Reply Extension [11]. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | AAA SPI | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | HA SPI | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Algorithm Identifier | Replay Method | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Key Material ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 2: The Unsolicited MN-HA Key Material From AAA Subtype-Specific Data AAA SPI A 32-bit opaque value, indicating the SPI that the mobile node must use to determine the algorithm to use for establishing the HA security information. HA SPI A 32-bit opaque value, which the mobile node MUST use to index all the necessary information established for the HA security information after it is decoded. Algorithm Identifier This field indicates the algorithm to be used for future computations of the MN-HA Authentication Extension (see section 2) Replay Method This field contains the replay method to be used for future Registration messages (see section 2). Key Material A random [4] value of at least 64 bits. The Unsolicited MN-HA Material Key From AAA subtype-specific data is shown in figure 2. The Mobile Node creates the MN-HA key using the Key Material provided by the home domain AAA server (AAAH). The key is intended for use the mobile node to secure future Mobile IP registrations with its home agent. The MN-HA Key Reply MUST appear in the Registration Reply before the MN-HA Authentication extension. Perkins, Calhoun Expires 10 Janueary 2002 [Page 8]
Internet Draft AAA Keys for Mobile IP 10 July 2001 Once the mobile node creates the MN-HA Key, by using the algorithm specified in the AAA SPI, it stores the HA Security Information indexed by the HA SPI in its list of Mobile Security Associations. The mobile node uses the Identification field data from the Registration Request as its initial synchronization data with the home agent. 6. MN-FA Key Request From AAA Subtype The MN-FA Key Request From AAA subtype data uses subtype 7 of the Generalized MN-FA Key Request Extension [11]. The MN-FA Key Request From AAA extension MUST appear in the Registration Request before the MN-AAA Authentication extension. 7. MN-HA Key Request From AAA Subtype The MN-HA Key Request From AAA subtype data uses subtype 7 of the Generalized MN-HA Key Request Extension [11]. The MN-HA Key Request From AAA extension MUST appear in the Registration Request before the MN-AAA Authentication extension. 8. Error Values Each entry in the following table contains the name of Code [10] to be returned in a Registration Reply, the value for the Code, and the section in which the error is first mentioned in this specification. Error Name Value Section ---------------------- ----- --------- MISSING_MN_FA 107 4 9. IANA Considerations The number for the Generalized MN-HA Key Reply Extension is taken from the numbering space defined for Mobile IP registration extensions defined in RFC 2002 [10] as extended in RFC 2356 [7]. The subtype address space for the Generalized MN-HA Key Reply extension is defined in this document. From this space, subtype value 1 is assigned to the Unsolicited MN-HA Key Material From AAA Subtype extension. Perkins, Calhoun Expires 10 Janueary 2002 [Page 9]
Internet Draft AAA Keys for Mobile IP 10 July 2001 The number assigned to the MN-FA Key Request From AAA Subtype extension was taken from the numbering space defined for the Generalized MN-FA Key Request Extension, defined in [11]. The number assigned to the Unsolicited MN-FA Key Material From AAA Subtype extension was taken from the numbering space defined for the Generalized MN-FA Key Reply Extension, defined in [11]. The number assigned to the MN-HA Key Request From AAA Subtype extension was taken from the numbering space defined for the Generalized MN-HA Key Request Extension, defined in [11]. The Code values specified for errors, listed in section 8, MUST NOT conflict with any other code values listed in RFC 2002, RFC 3024 [6], or RFC 2356 [7]. They are to be taken from the space of error values conventionally associated with rejection by the foreign agent (i.e., 64-127). Section 2 introduces the Algorithm Identifier namespace that requires IANA management. This specification makes use of 1-3, and all other values other than zero (0) are available for assignment via Standards Action [8]. Section 2 introduces the Replay Method Identifier namespace that requires IANA management. This specification makes use of 1-3, and all other values other than zero (0) are available for assignment via Standards Action [8]. 10. Security Considerations The extensions in this document are intended to provide the appropriate level of security for Mobile IP entities (mobile node, foreign agent, and home agent) to operate Mobile IP registration protocol. The security associations resulting from use of these extensions do not offer any higher level of security than what is already implicit in use of the security association between the mobile node and the AAA. Since the extensions defined in this specification only carries Key Material, which is used to derive keys, it does not expose any data that could be used in an attack aimed at recovering the key shared between the mobile node and the AAA. The authors do not believe this specification introduces new security risks. Perkins, Calhoun Expires 10 Janueary 2002 [Page 10]
Internet Draft AAA Keys for Mobile IP 10 July 2001 References [1] B. Aboba and M. Beadles. The Network Access Identifier. Request for Comments (Proposed Standard) 2486, Internet Engineering Task Force, January 1999. [2] P. Calhoun and C. E. Perkins. Mobile IP Foreign Agent Challenge/Response Extension. Request for Comments (Proposed Standard) 3012, Internet Engineering Task Force, December 2000. [3] P. Calhoun, A. Rubens, H. Akhtar, and E. Guttman. DIAMETER Base Protocol (work in progress). Internet Draft, Internet Engineering Task Force. draft-ietf-aaa-diameter-03.txt, May 2001. [4] D. Eastlake, 3rd, S. Crocker, and J. Schiller. Randomness Recommendations for Security. Request for Comments (Informational) 1750, Internet Engineering Task Force, December 1994. [5] H. Krawczyk, M. Bellare, and R. Canetti. HMAC: Keyed-Hashing for Message Authentication. Request for Comments (Informational) 2104, Internet Engineering Task Force, February 1997. [6] Editor G. Montenegro. Reverse Tunneling for Mobile IP, revised. Request for Comments (Proposed Standard) 3024, Internet Engineering Task Force, January 2001. [7] G. Montenegro and V. Gupta. Sun's SKIP Firewall Traversal for Mobile IP. Request for Comments (Informational) 2356, Internet Engineering Task Force, June 1998. [8] T. Narten and H. Alvestrand. Guidelines for Writing an IANA Considerations Section in RFCs. Request for Comments (Best Current Practice) 2434, Internet Engineering Task Force, October 1998. [9] National Institute of Standards and Technology. Secure Hash Standard. Technical Report NIST FIPS PUB 180-1, U.S. Department of Commerce, April 1995. [10] C. Perkins. IP Mobility Support. Request for Comments (Proposed Standard) 2002, Internet Engineering Task Force, October 1996. [11] C. Perkins and P. Calhoun. Generalized Key Distribution Extensions for Mobile IP (work in progress). draft-ietf-mobileip-gen-key-00.txt, July 2001. Perkins, Calhoun Expires 10 Janueary 2002 [Page 11]
Internet Draft AAA Keys for Mobile IP 10 July 2001 [12] C. Rigney, A. Rubens, W. Simpson, and S. Willens. Remote Authentication Dial In User Service (RADIUS). Request for Comments (Proposed Standard) 2865, Internet Engineering Task Force, June 2000. Addresses The working group can be contacted via the current chairs: Basavaraj Patil Phil Roberts Nokia Megisto Corp. 6000 Connection Dr. Suite 120 20251 Century Blvd Irving, TX. 75039 Germantown MD 20874 USA USA Phone: +1 972-894-6709 Phone: +1 847-202-9314 Email: Basavaraj.Patil@nokia.com Email: PRoberts@MEGISTO.com Questions about this memo can also be directed to the authors: Charles E. Perkins Pat R. Calhoun Communications Systems Lab Network & Security Center Nokia Research Center Sun Microsystems Laboratories 313 Fairchild Drive 15 Network Circle Mountain View, California 94043 Menlo Park, California 94025 USA USA Phone: +1-650 625-2986 Phone: +1 650-786-7733 EMail: charliep@iprg.nokia.com EMail: pcalhoun@eng.sun.com Fax: +1 650 625-2502 Fax: +1 650-786-6445 Perkins, Calhoun Expires 10 Janueary 2002 [Page 12]
