Network Working Group D. Nelson Internet-Draft Elbrys Networks, Inc. Intended status: Informational March 12, 2008 Expires: September 13, 2008 Crypto-Agility Requirements for Remote Dial-In User Service (RADIUS) draft-nelson-radext-crypto-agility-requirements-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 September 13, 2008. Abstract This memo describes the requirements for a Crypto-Agility solution for Remote Authentication Dial-In User Service (RADIUS). Requirements Language 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]. Nelson Expires September 13, 2008 [Page 1]
Internet-Draft RADIUS Crypto-Acility Requirements March 2008 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. General . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.2. The Charge . . . . . . . . . . . . . . . . . . . . . . . . 3 2. A Working Definition of Crypto-Agility . . . . . . . . . . . . 3 3. The Current State of RADIUS Encryption . . . . . . . . . . . . 4 4. The Requirements . . . . . . . . . . . . . . . . . . . . . . . 4 4.1. Overall Solution Approach . . . . . . . . . . . . . . . . . 4 4.2. Security Services . . . . . . . . . . . . . . . . . . . . . 4 4.3. Backwards Compatibility . . . . . . . . . . . . . . . . . . 5 4.4. Interoperability and Change Congtrol . . . . . . . . . . . 5 4.5. Scope of Work . . . . . . . . . . . . . . . . . . . . . . . 5 4.6. Applicability of Automated Key Management Requirements . . 6 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6 6. Security Considerations . . . . . . . . . . . . . . . . . . . . 6 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 7 8. Informative References . . . . . . . . . . . . . . . . . . . . 7 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 7 Intellectual Property and Copyright Statements . . . . . . . . . . 8 Nelson Expires September 13, 2008 [Page 2]
Internet-Draft RADIUS Crypto-Acility Requirements March 2008 1. Introduction 1.1. General This memo describes the requirements for a Crypto-Agility solution for Remote Authentication Dial-In User Service (RADIUS). This memo, when approved, reflects the consensus of the RADIUS Extensions Working Group of the IETF (RADEXT) as to the features, properties and limitations of the Crypto-Agility work item for RADIUS. It also defines the term "crypto-agility" as used in this context, and provides the motivations for undertaking and completing this work. The requirments defined in this memo peviously existed in e-mail messages posted to the RADEXT mailing list, which may be found in the archives of that list. The purpose of framing the requirements in this memo is to formalize and memorialize them for future reference, and to bring them explicitly to the attention of the IESG and the IETF Comunity, as we proceed with this work. 1.2. The Charge At the IETF-66 meeting, the RADEXT WG was asked by members of the Security Area Directorate to undertake the action item to prepare a formal description of a Crypto-Agility work item, and corresponding milestones in the RADEXT Charter. After consultation with one of the Security Area Directors, Russ Housley, text was intially propsed on the RADEXT WG mailing list on October 26, 2006. That text reads as follows: The RADEXT WG will review the security requirements for crypro- agility in IETF protocosl, and identify the deficiences of the existing RADIUS protocol specifications against these requirements. Specific attention will be paid to RFC 4962. The RADEXT WG will propose one of more Internet Drafts to remediate any identified deficiences in the crypto-agility properties of the RADIUS protocol. The known deficiencies include the issue of negotiation of substitute algorithms for the message digest functions, the key-wrap functions, and the password-hiding function. Additionally, at least one mandatory to implement algorithm will be defined in each of these areas, as required. 2. A Working Definition of Crypto-Agility A generalized defintion of crypto-agility was offered up at the RADEXT WG sesion during IETF-68. Crypto-Agility is the ability for a protocol to adapt to evolving cryptography and security requirements. Nelson Expires September 13, 2008 [Page 3]
Internet-Draft RADIUS Crypto-Acility Requirements March 2008 This may include the provision of a modular mechamism to allow cryptographic algorithms to be updated without substantial disruption to fielded implemenations. It may provide for the dynamic negotiation and installation of cryptographic algorithms within protocol implementations (think of Dynamic-Link Libraries (DLL)). In the specific context of the RADIUS protocol and RADIUS implementations, Crypto-Agility may be better defined as the ability of RADIUS implementations to negotiate cryptographic algorithms for use in RADIUS exchanges, including the cryptographic algorithms used to protect RADIUS packets and to hide RADIUS atributes. This capability covers all RADIUS message types: Access-Request/Response, Acounting-Request/Response, and CoA/Disconnect-Request/Response. 3. The Current State of RADIUS Encryption RADIUS packets, as defined in RFC 2865, are protected by an MD5-baed messge integrity check (MIC), within the Authenticator field of RADIUS packest other than Access-Request. The Message-Authenticator Attribute utilizes HMAC-MD5 to authenticate and integrity protect RADIUS packets. Various RADIUS attributes support hidden values, including: User-Password, Tunnel-Password, and variosu Vendor- Specific Attributes. Generally speaking, the hiding mechanism uses a stream cipher based on a key stream from an MD5 digest. Recent work on MD5 collisions does not immediately compromise any of these methods, absent knowledge of the RADIUS sharfed secret. However, the progress toward compromise of MD5's basic cryptographic assumptions has resulted in the deprecation of MD5 usage in a variety of applications. 4. The Requirements 4.1. Overall Solution Approach RADIUS crypto-agility solutions are not restricted to utilizing technology described in existing RFCs. Since RADIUS over IPsec is already described in RFC 3162 and 3579, this technique is already available to those who wish to use it. Therefore it is expected that proposals will utilize other techniques. 4.2. Security Services Proposals MUST support the negotiation of cryptographic algorithms for per-packet integrity/authentication protection. Support for confidentiality of entire RADIUS packets is OPTIONAL. However, Nelson Expires September 13, 2008 [Page 4]
Internet-Draft RADIUS Crypto-Acility Requirements March 2008 proposals MUST support the negotiation of algorithms for encryption (sometimes referred to as "hiding") of RADIUS attributes. If possible, it is desirable for proposals to provide for the encryption of existing attributes. This includes existing "hidden" attributes as well as attributes (such as location attributes) that require confidentiality. Included in negotiation techniques are "hint and consent" mechanisms where the NAS provides a list of algorithms and the server selects one. Proposals MUST support replay protection. The existing mechanisms for replay protection are considered adequate and should be maintained. Crypto-agility solutions MUST specify mandatory-to-implemenalgorithms for each mechanism. 4.3. Backwards Compatibility Solutions to the problem MUST demonstrate backward compatibility with existing RADIUS implementations. That is, a crypto-agility solution needs to be able to send packets that a legacy RADIUS client or server will receive and process successfully. Similarly, a crypto- agility solution needs to be capable of receiving and processing packets from a legacy RADIUS client or server. Crypto-agility solutions MUST avoid security compromise, even in situations where the existing cryptographic algorithms utilized by RADIUS implementations are shown to be weak enough to provide little or no security (e.g. in event of compromise of the "legacy" RADIUS shared secret). Included in this would be protection against bidding down attacks. 4.4. Interoperability and Change Congtrol Proposals MUST indicate a willingness to cede change control to the IETF. Crypto-agility solutions MUST be interoperable between independent implementations based purely on the information provided in the specification. 4.5. Scope of Work Crypto-agility solutions MUST apply to all RADIUS packet types, including Access-Request, Access-Challenge, Access-Reject, Access- Accept, Accounting-Request, Accounting-Response, and CoA/Disconnect Nelson Expires September 13, 2008 [Page 5]
Internet-Draft RADIUS Crypto-Acility Requirements March 2008 messages. Proposals MUST include a Diameter compatibility section, although it is expected that the work will occur purely within RADIUS or in the transport, and therefore does not affect message data that is exchanged with Diameter. Crypto-agility solutions SHOULD NOT require fundamental changes to The RADIUS operational model, such as the introduction of new commands Or maintenance of state on the RADIUS server. Similarly, a proposal Should focus on the crypto-agility problem and nothing else. For example, proposals should not require new attribute formats or include definition of new RADIUS services. Unless modified, the restrictions in the RADEXT WG charter apply. Note that for the purposes of this work, the RADEXT WG charter restriction against definition of "new security mechanisms" should be interpreted as prohibiting changes to the basic RADIUS packet format (e.g. headers), but permits new crypto-algorithms to be substituted for use in existing security mechanisms. 4.6. Applicability of Automated Key Management Requirements At the IETF-70 meeting, and leading up to that meeting, the RADEXT WG debated whether or not RFC 4107 would require a RADIUS Crypto-Agility solution to feaure Automated Key Management (AKM). It was pointed out that RFC 4107 only requires AKM for protoocls that involve O(n^2) keys. This does not apply to RADIUS deplyments, which require O(n) keys. The consensus of the RADEXT WG is that RADIUS Crypro-Agility solutions do not need to provide AKM, and that appropriate security considerations text would be drafted to explain why the AKM provisions of RFC 4107 do not apply. 5. IANA Considerations This document makes no request of IANA. Note to RFC Editor: this section may be removed on publication as an RFC. 6. Security Considerations This specification describes the requirements for new cryptographic protection mechanisms, including the modular selection of algorithms and modes. Therefore, the subject matter of this memo is all about security. Nelson Expires September 13, 2008 [Page 6]
Internet-Draft RADIUS Crypto-Acility Requirements March 2008 7. Acknowledgements TBS 8. Informative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2865] Rigney, C., Willens, S., Rubens, A., and W. Simpson, "Remote Authentication Dial In User Service (RADIUS)", RFC 2865, June 2000. [RFC3162] Aboba, B., Zorn, G., and D. Mitton, "RADIUS and IPv6", RFC 3162, August 2001. [RFC3579] Aboba, B. and P. Calhoun, "RADIUS (Remote Authentication Dial In User Service) Support For Extensible Authentication Protocol (EAP)", RFC 3579, September 2003. [RFC4107] Bellovin, S. and R. Housley, "Guidelines for Cryptographic Key Management", BCP 107, RFC 4107, June 2005. [RFC4962] Housley, R. and B. Aboba, "Guidance for Authentication, Authorization, and Accounting (AAA) Key Management", BCP 132, RFC 4962, July 2007. Author's Address David Nelson Elbrys Networks, Inc. 75 Rochester Ave, Unit #3, Portsmouth, NH 03801 USA Phone: +1.603.570.2636 Email: dnelson@elbrysnetworks.com Nelson Expires September 13, 2008 [Page 7]
Internet-Draft RADIUS Crypto-Acility Requirements March 2008 Full Copyright Statement Copyright (C) The IETF Trust (2008). 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. 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, THE IETF TRUST 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. Intellectual Property 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. Nelson Expires September 13, 2008 [Page 8]