Network Working Group R. Housley Internet Draft Vigil Security June 2005 Bernard Aboba Expires in six months Microsoft AAA Key Management 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. Abstract This document provides guidance to designers of AAA key management protocols. Given the complexity and difficulty in designing secure, long-lasting key management algorithms and protocols by experts in the field, it is almost certainly inappropriate for IETF working groups without deep expertise in the area to be designing their own key management algorithms and protocols based on Authentication, Authorization and Accounting (AAA) protocols. The guidelines in this document apply to documents requesting publication as RFCs, as well as to use of AAA key management by any other standards development organizations (SDOs). Housley & Aboba [Page 1] Internet Draft draft-housley-aaa-key-mgmt-00.txt June 2005 Table of Contents {{{ Fill in later. }}} 1. Introduction This document provides architectural guidance to designers of AAA key management protocols. Given the complexity and difficulty in designing secure, long-lasting key management algorithms and protocols by experts in the field, it is almost certainly inappropriate for IETF working groups without deep expertise in the area to be designing their own key management algorithms and protocols based on Authentication, Authorization and Accounting (AAA) protocols. These guidelines apply to documents requesting publication as RFCs as well as to use of AAA key management by any standards development organization (SDO) that depend on IETF specifications for protocols such as EAP [RFC3748], RADIUS [RFC2865] and Diameter [RFC3588]. In March 2003, at the IETF 56 AAA Working Group Session, Russ Housley gave a presentation on "Key Management in AAA" [H]. That presentation established the vast majority of the requirements contained in this document. 1.1. Requirements Specification The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD, SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL, when they appear in this document, are to be interpreted as described in RFC 2119 [RFC2119]. An AAA key management proposal is not compliant with this specification if it fails to satisfy one or more of the MUST or MUST NOT statements. An AAA key management proposal that satisfies all the MUST, MUST NOT, SHOULD and SHOULD NOT statements is said to be "unconditionally compliant"; one that satisfies all the MUST and MUST NOT statements but not all the SHOULD or SHOULD NOT requirements is said to be "conditionally compliant". Housley & Aboba [Page 2] Internet Draft draft-housley-aaa-key-mgmt-00.txt June 2005 1.2. Terminology This section defines terms that are used in this document. AAA Authentication, Authorization and Accounting (AAA). AAA protocols include RADIUS [RFC2865] and Diameter [RFC3588]. Authenticator The end of the link initiating EAP authentication. The term authenticator is used in [IEEE-802.1X], and authenticator has the same meaning in this document. Backend authentication server A backend authentication server is an entity that provides an authentication service to an authenticator. This terminology is also used in [802.1X]. CHAP Challenge Handshake Authentication Protocol; a one-way challenge/response authentication protocol defined in [RFC1994]. EAP Extensible Authentication Protocol, defined in [RFC3748]. EAP server The entity that terminates the EAP authentication method with the peer. In the case where no backend authentication server is used, the EAP server is part of the authenticator. In the case where the authenticator operates in pass-through mode, the EAP server is located on the backend authentication server. PAP Password Authentication Protocol; a deprecated cleartext password PPP authentication protocol, originally defined in [RFC1334]. Housley & Aboba [Page 3] Internet Draft draft-housley-aaa-key-mgmt-00.txt June 2005 Party A party is a processing entity which can be identified as a single role in a protocol. Peer The end of the link that responds to the authenticator. In [802.1X], this end is known as the supplicant. PPP Point-to-Point Protocol, defined in [RFC1661], provides support for multiprotocol serial datalinks. PPP is the primary IP datalink used for dial-in NAS connection service. Secure Association Protocol A protocol for managing security associations derived from EAP and/or AAA exchanges. An example of a Secure Association Protocols is the 4-way handshake defined within [802.11i]. Supplicant The end of the link that responds to the authenticator in [802.1X]. Network Access Server A device which provides an access service for a user to a network. The service may be a network connection, or a value added service such as terminal emulation, as described in [RFC2881]. 4-Way Handshake A pairwise Authentication and Key Management Protocol (AKMP) defined in [802.11i], which confirms mutual possession of a Pairwise Master Key by two parties and distributes a Group Key. Housley & Aboba [Page 4] Internet Draft draft-housley-aaa-key-mgmt-00.txt June 2005 2. AAA Key Management History Protocols for Authentication, Authorization and Accounting (AAA) were originally developed to support deployments of Network Access Servers (NASes) providing access to the Internet via PPP [RFC1661]. In deployments supporting more than a modest number of users, it became impractical for each NAS to contain its own list of users and associated credentials. As a result, protocols for AAA were developed, including TACACS [RFC1492], RADIUS [RFC2865] and Diameter [RFC3588]. These protocols enabled a central AAA server to authenticate users requesting network access, as well as providing authorization and accounting. While PPP [RFC1661] originally supported only PAP [RFC1334] and CHAP [RFC1661] authentication, the limitations of these authentication mechanisms became apparent. For example, both PAP and CHAP are unilateral authentication schemes supporting only authentication of the PPP peer to the NAS. Since PAP is a cleartext password scheme, it is vulnerable to snooping by an attacker with access to the conversation between the PPP peer and NAS. In addition, the use of PAP creates vulnerabilities within RADIUS as described in Section 4.3 of [RFC3579]. As a result, use of PAP is deprecated. While CHAP, a challenge-response scheme based on MD5, offers better security than cleartext passwords, it does not provide for mutual authentication, and CHAP is vulnerable to dictionary attack. With the addition of the Encryption Control Protocol (ECP) to PPP [RFC1968] as well as the definition of PPP ciphersuites in [RFC2419] [RFC2420][RFC3078] the need arose to provide keying material for use with link layer ciphersuites. As with user authentication, provisioning of static keys on each NAS did not scale well. Additional vendor-specific PPP authentication protocols such as MS- CHAP [RFC2433] and MS-CHAPv2 [RFC2759] were developed to provide mutual authentication as well as key derivation [RFC3079] for use with negotiated ciphersuites, and they were subsequently adapted for use with PPP-based VPNs [RFC2637]. As with PAP and CHAP, flaws were subsequently found in these new mechanisms [SM1][SM2]. Even though PPP provided for negotiation of authentication algorithms, addressing the vulnerabilities found in authentication mechanisms still proved painful, since new code needed to be deployed on PPP peers as well as on the AAA server. In order to enable more rapid deployment of new authentication mechanisms, as well as fixes for vulnerabilities found in existing methods, the Extensible Authentication Protocol (EAP) [RFC3748] was developed, along with support for centralized authentication via RADIUS/EAP [RFC3579]. Housley & Aboba [Page 5] Internet Draft draft-housley-aaa-key-mgmt-00.txt June 2005 By enabling "pass through" authentication on the NAS, EAP enabled deployment of new authentication methods or updates to existing methods by revising code only on the EAP peer and AAA server. The initial authentication mechanisms defined in [RFC2284] (MD5-Challenge, One-Time Password (OTP), and Generic Token Card (GTC)) only supported unilateral authentication, and these mechanisms do not support key derivation. Subsequent authentication methods such as EAP-TLS [RFC2716] supported mutual authentication and key derivation. In order to support the provisioning of dynamic keying material for link layer ciphersuites in an environment supporting centralized authentication, a mechanism was needed for the transport of keying material between the AAA server and NAS. Vendor-specific RADIUS attributes were developed for this purpose [RFC2548]. Vulnerabilities were subsequently found in the key wrap technique, as described in Section 4.3 of [RFC3579]. In theory, public key authentication mechanisms such as EAP-TLS are capable of supporting mutual authentication and key derivation between the EAP peer and NAS without requiring AAA key distribution, as described in [A]. However, in practice such pure two-party schemes are rarely deployed. Operation of a centralized AAA server significantly reduces the effort required to deploy certificates to NASes, and even though a AAA server may not be required for key derivation and possibly authentication, its participation is required for service authorization and accounting. "Pass-through" authentication and AAA key distribution has retained popularity even in the face of rapid improvements in processor and memory capabilities. In addition to producing NAS devices of increased capability for enterprise and carrier customers, implementers have also produced low cost/high volume NAS devices such as 802.11 Access Points, causing the resources available on an average NAS to increase more slowly than Moore's law. Despite widespread support for certificate handling and sophisticated key derivation mechanisms such as IKEv1 [RFC2409] within host operating systems, these security capabilities are rarely deployed on low-end NASes and clients. Even on more capable NASes, such as VPN servers, centralized authentication and AAA key management has proven popular. For example, one of the major limitations of IKEv1 [RFC2409] was the lack of integration with EAP and AAA, requiring proprietary extensions to enable use of IPsec VPNs by organizations deploying password or authentication tokens. These limitations were addressed in IKEv2 [RFCxxxx], which while handling key derivation solely between the VPN client and server, supports EAP methods for user authentication. In Housley & Aboba [Page 6] Internet Draft draft-housley-aaa-key-mgmt-00.txt June 2005 order to enable cryptographic binding of EAP user authentication to keys derived within the IKEv2 exchange, the transport of EAP-derived keys within AAA is required where the selected EAP method supports key derivation. 3. AAA Environment Concerns EAP is being used in new ways. The inclusion of support for EAP within IKEv2 and the standardization of robust Wireless LAN security [802.11i] based on EAP are two examples. EAP has also been proposed within IEEE 802.16e [802.16e]. AAA-based key management is being incorporated into standards developed by the IETF and other standards development organizations (SDOs), such as IEEE 802. However, due to ad hoc development of AAA-based key management, AAA-based key distribution schemes have poorly understood security properties, even when well- studied cryptographic algorithms are employed. More academic research is needed to fully understand the security properties of AAA-based key management in the diverse protocol environments where it is being employed today. In the absence of research results, pragmatic guidance based on sound security engineering principles is needed. EAP selects one end-to-end authentication mechanism. The mechanisms defined in [RFC3748] only support unilateral authentication, and they do not support mutual authentication or key derivation. As a result, these mechanisms do not fulfill the security requirements for many deployment scenarios, including Wireless LAN authentication [RFC4017]. To ensure adequate security and interoperability, EAP applications need to specify mandatory-to-implement algorithms. As described in [RFC3748], EAP methods seeking publication as an RFC need to document their security claims; however, since the authentication algorithms are not based on well-studied models, the validity of these security claims may be very difficult to determine. In addition to the need for interoperability, cryptographic algorithm independent solutions are greatly preferable. Without algorithm independence, the protocol must be changed whenever a problem is discovered with the selected algorithm. As the AAA history shows, problems are inevitable. Problems can surface due to age or design failure. DES [FIPS46] was a well designed encryption algorithm, and it provided protection for many years. Yet, the 56-bit key size was eventually overcome by Moore's Law. No cryptographic deficiencies have been discovered in DES. Housley & Aboba [Page 7] Internet Draft draft-housley-aaa-key-mgmt-00.txt June 2005 Examples of serious flaws plague the history of key management protocol development, starting with the very first attempt to define a key management protocol in the open literature, which was published in 1978 [NS]. A flaw and a fix were published in 1981 [DS], and the fix was broken in 1994 [AN]. In 1995 [L], a new flaw was found in the original 1978 version, in an area not affected by the 1981/1994 issue. All of these flaws were blindingly obvious once described, yet no one spotted them earlier. Note that the original protocol, if it were revised to employ certificates, which of course had yet to be invented, was only three messages. Many proposed AAA key management schemes are significantly more complicated. This bit of history shows that key management protocols are subtle. Experts can easily miss a flaw. As a result, peer review by multiple experts is essential. The history of AAA underlines the importance of algorithm independence as flaws have been found in authentication mechanisms such as CHAP, MS-CHAPv1 [SM1], MS-CHAPv2 [SM2], Kerberos [W][BM][DLS], and LEAP [B]. Unfortunately, RADIUS [RFC2865] mandates use of the MD5 algorithm for integrity protection, which has known deficiencies, and RADIUS has no provisions to negotiate substitute algorithms. Similarly, the vendor-specific key wrap mechanism defined in [RFC2548] has no provisions to negotiate substitute algorithms. The principle of least privilege is an important design guideline. AAA key management schemes need to be designed in a manner where each party has only the privileges necessary to perform their role. That is, no party should have access to any keying material that is not needed to perform their own role. A party has access to a particular key if it has access to all of the secret information needed to derive it. In the context of EAP, the EAP peer and server are the parties involved in the EAP method conversation, and they gain access to key material when the conversation completes successfully. However, the lower layer needs keying material to be provided to the peer and authenticator. As a result, a "pass-through" mode is used to provide the keying material, and the lower layer keying material is replicated from the AAA server to the authenticator. The only parties authorized to obtain all of the keying material are the EAP peer and server; the authenticator obtains only the keying material necessary for its specific role. No other party can obtain access to any of the keying material. Housley & Aboba [Page 8] Internet Draft draft-housley-aaa-key-mgmt-00.txt June 2005 4. AAA Key Management Requirements This section provides guidance to AAA protocol designers and EAP method designers. Acceptable solutions MUST meet all of these requirements. Cryptographic algorithm independent The AAA key management protocol MUST be cryptographic algorithm independent. However, an EAP method MAY depend on a specific cryptographic algorithm. The ability to negotiate the use of a particular cryptographic algorithm provides resilience against compromise of a particular cryptographic algorithm. The AAA protocol MUST be algorithm independent, both in terms of its own security mechanisms as well as mechanisms supported for user authentication. Algorithm independence is also REQUIRED with a Secure Association Protocol if one is defined. This is usually accomplished by including an algorithm identifier in the protocol, and by specifying the algorithm requirements in the protocol specification. For interoperability, at least one suite of mandatory-to-implement algorithms MUST be selected. Note that without protection by IPsec as described in [RFC3579] Section 4.2, RADIUS [RFC2865] does not meet this requirement, since the integrity protection algorithm can not be negotiated. This requirement does not mean that a protocol must support both public-key and symmetric-key cryptographic algorithms. It means that the protocol needs to be structured in such a way that multiple public-key algorithms can be used whenever a public-key algorithm is employed. Likewise, it means that the protocol needs to be structured in such a way that multiple symmetric-key algorithms can be used whenever a symmetric-key algorithm is employed. Strong, fresh session keys While preserving algorithm independence, session keys MUST be strong and fresh. Each session deserves an independent session key. Fresh keys are required even when a long replay counter (that is, one that "will never wrap") is used to ensure that loss of state does not cause the same counter value to be used more than once with the same session key. Some EAP methods are capable of deriving keys of varying strength, and these EAP methods MUST permit the generation of keys meeting a minimum equivalent key strength as defined in [RFC3766]. Housley & Aboba [Page 9] Internet Draft draft-housley-aaa-key-mgmt-00.txt June 2005 A fresh cryptographic key is one that is generated specifically for the intended use. In this situation, a post-EAP handshake is used to establish session keys. Thus, the AAA protocol and EAP method MUST ensure that the keying material supplied as an input to session key derivation is fresh, and the post-EAP handshake MUST generate a separate session key for each session, even if the keying material provided by EAP is cached. Further, the keys MUST NOT be dependent on one another. That is, disclosure of one session key does not aid the attacker in discovering any other session keys. Limit key scope Follow the principle of least privilege. Parties MUST NOT have access to keying material that is not needed to perform their own role. A party has access to a particular key if it has access to all of the secret information needed to derive it. A post-EAP handshake is used to establish session keys, and the post-EAP handshake MUST specify the scope for session keys. Replay detection mechanism The AAA key management protocol exchanges MUST MUST be replay protected, including AAA, EAP and Secure Association Protocol exchanges. Replay protection allows a protocol message recipient to discard any message that was recorded during a previous legitimate dialogue and presented as though it belonged to the current dialogue. Authenticate all parties Each party in the AAA key management protocol MUST be authenticated to the other parties with whom it communicates. Authentication mechanisms MUST maintain the confidentiality of any secret values used in the authentication process. A post-EAP handshake is used to establish session keys, and the parties involved in the post-EAP handshake MUST identify themselves using identities that are meaninful in the lower layer protocol environment that will employ the session keys. Authentication mechanisms MUST NOT employ plaintext passwords. Peer and authenticator authorization Peer and authenticator authorization MUST be performed. Authorization is REQUIRED whenever a peer associates with a new Housley & Aboba [Page 10] Internet Draft draft-housley-aaa-key-mgmt-00.txt June 2005 authenticator. The authorization checking prevents an elevation of privilege attack, and it ensures that an unauthorized authenticator is detected. Authorizations SHOULD be synchronized between the EAP peer, server, authenticator. Once the AAA key management protocol exchanges are complete, all of these parties should hold view of the authorizations associated the other parties. Keying material confidentiality While preserving algorithm independence, confidentiality of all keying material MUST be maintained. Confirm ciphersuite selection The selection of the "best" ciphersuite MUST be securely confirmed. The mechanism MUST detect attempted roll back attacks. Uniquely name keys AAA key management proposals require a robust key naming scheme, particularly where key caching is supported. Objects that cannot be named cannot be managed. All keys MUST be uniquely named, and the key name MUST NOT be based on the keying material itself. Prevent the Domino effect Compromise of a single authenticator MUST NOT compromise any other part of the system, especially session keys and long-term keys. There are many implications of this requirement; however, two implication deserves highlighting. First, an authenticator MUST NOT share any keying material with another authenticator. Second, the scope of the authenticator needs to be defined and understood by all parties that communicate with it. Housley & Aboba [Page 11] Internet Draft draft-housley-aaa-key-mgmt-00.txt June 2005 Bind key to its context Keying material MUST be bound to the appropriate context, which includes: o The manner in which the keying material is expected to be used; o The other parties that are expected to have access to the keying material; and o The expected lifetime of the keying material. Any party with legitimate access to keying material can determine its context. In addition, the protocol MUST ensure that all parties with legitimate access to keying material have the same context for the keying material. This requires that the parties are properly identified and authenticated, so that all of the parties that have access to the keying material can be determined. The context will include the EAP peer and authenticator identities in more than one form. One (or more) name form is needed to identify these parties in the AAA protocol and EAP menthod. Another name form is needed to identify these parties within lower layer that will employ the session key. 5. AAA Key Management Recommendations Acceptable solutions SHOULD meet all of these requirements. Confidentiality of Identity In many environments it is important to provide confidentiality protection for identities. However, this is not important in other environments. For this reason, EAP methods SHOULD provide a mechanism for identity protection of EAP peers, but such protection is not a requirement. Housley & Aboba [Page 12] Internet Draft draft-housley-aaa-key-mgmt-00.txt June 2005 Authorization restriction If peer authorization is restricted, then the peer SHOULD be made aware of the restriction. Otherwise, the peer may inadvertently attempt to circumvent the restriction. Authorization restrictions include: o Key lifetimes, where the keying material can only be used for a certain period of time; o SSID restrictions, where the keying material can only be used with a specific IEEE 802.11 SSID; o Called-Station-ID restrictions, where the keying material can only be used with a single IEEE 802.11 BSSID; and o Calling-Staton-ID restrictions, where the keying material can only be used with a single peer IEEE 802 MAC address. 6. Security Considerations {{{ To be provided. }}} 7. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", RFC 2119, March, 1997. 8. Informative References [802.1X] IEEE Standards for Local and Metropolitan Area Networks: Port based Network Access Control, IEEE Std 802.1X-2004, December 2004. [802.11i] Institute of Electrical and Electronics Engineers, "Supplement to Standard for Telecommunications and Information Exchange Between Systems -- LAN/MAN Specific Requirements - Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications: Specification for Enhanced Security", IEEE 802.11i, July 2004. Housley & Aboba [Page 13] Internet Draft draft-housley-aaa-key-mgmt-00.txt June 2005 [802.16e] Institute of Electrical and Electronics Engineers, "Supplement to Standard for Telecommunications and Information Exchange Between Systems -- LAN/MAN Specific Requirements - Part 16: Air Interface for Fixed and Mobile Broadband Wireless Access Systems -- Amendment for Physical and Medium Access Control Layers for Combined Fixed and Mobile Operation in Licensed Bands", Draft, IEEE 802.16e/D8, May 2005. [A] Aboba, B., "Certificate-Based Roaming", Internet-Draft, draft-ietf-roamops-cert-02 (work in progress), April 1999. [AN] M. Abadi and R. Needham, "Prudent Engineering Practice for Cryptographic Protocols", Proc. IEEE Computer Society Symposium on Research in Security and Privacy, May 1994. [B] Brewin, B., "LEAP attack tool author says he wants to alert users to risks", Computerworld, October 17, 2003. [BM] Bellovin, S. and M. Merrit, "Limitations of the Kerberos authentication system", Proceedings of the 1991 Winter USENIX Conference, pp. 253-267, 1991. [DLS] Dole, B., Lodin, S. and E. Spafford, "Misplaced trust: Kerberos 4 session keys", Proceedings of the Internet Society Network and Distributed System Security Symposium, pp. 60-70, March 1997. [DS] D. Denning and G. Sacco. "Timestamps in key distributed protocols", Communication of the ACM, 24(8):533--535, 1981. [FIPS46] Federal Information Processing Standards Publication (FIPS PUB) 46, Data Encryption Standard, 1977 January 15. [H] Housley, R., "Key Management in AAA", Presentation to the AAA WG at IETF 56, March 2003, http://www.ietf.org/proceedings/03mar/slides/aaa-5/ index.html. [L] G. Lowe. "An attack on the Needham-Schroeder public key authentication protocol", Information Processing Letters, 56(3):131--136, November 1995. [NS] R. Needham and M. Schroeder. "Using encryption for authentication in large networks of computers", Communications of the ACM, 21(12), December 1978. Housley & Aboba [Page 14] Internet Draft draft-housley-aaa-key-mgmt-00.txt June 2005 [RFC1334] Lloyd, B. and B. Simpson, "PPP Authentication Protocols" RFC 1334, October 1992, Obsoleted by RFC 1994. [RFC1492] Finseth, C., "An Access Control Protocol, Sometimes Called TACACS", RFC 1492, July 1993. [RFC1661] Simpson, W., "The Point-to-Point Protocol (PPP)", RFC 1661, July 1994. [RFC1968] Meyer, G., "The PPP Encryption Protocol (ECP)", RFC 1968, June 1996. [RFC1994] Simpson, W., "PPP Challenge Handshake Authentication Protocol (CHAP)", RFC 1994, August 1996. [RFC2409] Harkins, D. and D. Carrel, "The Internet Key Exchange (IKE)", RFC 2409, November 1998. [RFC2419] Sklower, K. and G. Meyer, "The PPP DES Encryption Protocol, Version 2 (DESE-bis)", RFC 2419, September 1998. [RFC2420] Hummert, K., "The PPP Triple-DES Encryption Protocol (3DESE)", RFC 2420, September 1998. [RFC2433] Zorn, G. and S. Cobb, "Microsoft PPP CHAP Extensions", RFC 2433, October 1998. [RFC2548] Zorn, G., "Microsoft Vendor-specific RADIUS Attributes", RFC 2548, March 1999. [RFC2637] Hamzeh, K., Pall, G., Verthein, W., Taarud, J., Little, W. and G. Zorn, "Point-to-Point Tunneling Protocol (PPTP)", RFC 2637, July 1999. [RFC2716] Aboba, B. and D. Simon, "PPP EAP TLS Authentication Protocol", RFC 2716, October 1999. [RFC2759] Zorn, G., "Microsoft PPP CHAP Extensions, Version 2", RFC 2759, January 2000. [RFC2865] Rigney, C., Willens, S., Rubens, A. and W. Simpson, "Remote Authentication Dial In User Service (RADIUS)", RFC 2865, June 2000. [RFC2881] D. Mitton, M. Beadles, "Network Access Server Requirements Next Generation (NASREQNG) NAS Model", RFC 2881, July 2000. Housley & Aboba [Page 15] Internet Draft draft-housley-aaa-key-mgmt-00.txt June 2005 [RFC3078] Pall, G. and G. Zorn, "Microsoft Point-To-Point Encryption (MPPE) Protocol", RFC 3078, March 2001. [RFC3079] Zorn, G., "Deriving Keys for use with Microsoft Point-to- Point Encryption (MPPE)", RFC 3079, March 2001. [RFC3579] Aboba, B. and P. Calhoun, "RADIUS (Remote Authentication Dial In User Service) Support For Extensible Authentication Protocol (EAP)", RFC 3579, September 2003. [RFC3588] Calhoun, P., Loughney, J., Guttman, E., Zorn, G. and J. Arkko, "Diameter Base Protocol", RFC 3588, September 2003. [RFC3748] Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J. and H. Levkowetz, "Extensible Authentication Protocol (EAP)", RFC 3748, June 2004. [RFC3766] Orman, H. and P. Hoffman, "Determining Strength for Public Keys Used For Exchanging Symmetric Keys", RFC 3766, April 2004. [RFC4017] Stanley, D., Walker, J. and B. Aboba, "Extensible Authentication Protocol (EAP) Method Requirements for Wireless LANs", RFC 4017, March 2005. [RFCxxxx] Kaufman, C., "Internet Key Exchange (IKEv2) Protocol", Internet-Draft, draft-ietf-ipsec-ikev2-17 (work in progress; in RFC Editor queue), September 2004. [SM1] Schneier, B. and Mudge, "Cryptanalysis of Microsoft's Point-to-Point Tunneling Protocol", Proceedings of the 5th ACM Conference on Communications and Computer Security, ACM Press, November 1998. [SM2] Schneier, B. and Mudge, "Cryptanalysis of Microsoft's PPTP Authentication Extensions (MS-CHAPv2)", CQRE 99, Springer-Verlag, 1999, pp. 192-203. [W] Wu, T., "A Real-World Analysis of Kerberos Password Security", Proceedings of the 1999 ISOC Network and Distributed System Security Symposium, http://www.isoc.org/isoc/conferences/ndss/99/ proceedings/papers/wu.pdf. Housley & Aboba [Page 16] Internet Draft draft-housley-aaa-key-mgmt-00.txt June 2005 Acknowledgments Many thanks to James Kempf for his quality review and encouragement. Authors' Address Russell Housley Vigil Security, LLC 918 Spring Knoll Drive Herndon, VA 20170 USA Email: housley@vigilsec.com Phone: +1 703-435-1775 Bernard Aboba Microsoft Corporation One Microsoft Way Redmond, WA 98052 USA Email: bernarda@microsoft.com Phone: +1 425 706 6605 Fax: +1 425 936 7329 Intellectual Property Statement The IETF has been notified of intellectual property rights claimed in regard to some or all of the specification contained in this document. For more information consult the online list of claimed rights. 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. Housley & Aboba [Page 17] Internet Draft draft-housley-aaa-key-mgmt-00.txt June 2005 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 (2005). 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. Housley & Aboba [Page 18]