Network Working Group D. Nelson Internet-Draft Elbrys Networks, Inc. Intended status: Informational March 3, 2011 Expires: September 3, 2011 Crypto-Agility Requirements for Remote Dial-In User Service (RADIUS) draft-ietf-radext-crypto-agility-requirements-02.txt Abstract This memo describes the requirements for a crypto-agility solution for Remote Authentication Dial-In User Service (RADIUS). Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and 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 3, 2011. 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 3, 2011 [Page 1]
Internet-Draft RADIUS Crypto-Agility Requirements March 2011 Copyright Notice Copyright (c) 2011 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. 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 Control . . . . . . . . . . . . 6 4.5. Scope of Work . . . . . . . . . . . . . . . . . . . . . . . 6 4.6. Applicability of Automated Key Management Requirements . . 6 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7 6. Security Considerations . . . . . . . . . . . . . . . . . . . . 7 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 7 8. Informative References . . . . . . . . . . . . . . . . . . . . 7 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 8 Nelson Expires September 3, 2011 [Page 2]
Internet-Draft RADIUS Crypto-Agility Requirements March 2011 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 requirements defined in this memo have previously been expressed in e-mail messages posted to the RADEXT WG 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 Community, 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 initially proposed on the RADEXT WG mailing list on October 26, 2006. That text reads as follows: The RADEXT WG will review the security requirements for crypto- agility in IETF protocols, and identify the deficiencies of the existing RADIUS protocol specifications against these requirements. Specific attention will be paid to RFC 4962. The RADEXT WG will propose one or more Internet Drafts to remediate any identified deficiencies 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 definition of crypto-agility was offered up at the RADEXT WG session during IETF-68. Crypto-Agility is the ability for a protocol to adapt to evolving cryptography and security Nelson Expires September 3, 2011 [Page 3]
Internet-Draft RADIUS Crypto-Agility Requirements March 2011 requirements. This may include the provision of a modular mechanism to allow cryptographic algorithms to be updated without substantial disruption to fielded implementations. 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 Attributes. This capability covers all RADIUS message types: Access-Request/Response, Accounting-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 message integrity check (MIC), within the Authenticator field of RADIUS packets 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 various 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 shared 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 RFC 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 Nelson Expires September 3, 2011 [Page 4]
Internet-Draft RADIUS Crypto-Agility Requirements March 2011 confidentiality of entire RADIUS packets is OPTIONAL. However, 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. Proposals MUST support replay protection. The existing mechanisms for replay protection are considered adequate and should be maintained. 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. Crypto-agility solutions MUST specify mandatory-to-implement algorithms for each defined 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. Proposals MUST NOT introduce new capabilities negotation features into the RADIUS protocol, but rather MUST use the existing mechanisms. Included in such negotiation techniques are "hint and accept" and "hint and reject" mechanisms, where the NAS (RADIUS client) provides a list of supported algorithms and the RADIUS server selects one. Crypto-agility solutions SHOULD NOT require changes to the RADIUS operational model, such as the introduction of new commands or maintenance of [additional] 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. Nelson Expires September 3, 2011 [Page 5]
Internet-Draft RADIUS Crypto-Agility Requirements March 2011 4.4. Interoperability and Change Control 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 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. Proposals MUST discuss any inherent assumptions about, or limitations on, client/server operations or deployment and SHOULD provide recommendations for transition of deployments from legacy RADIUS to crypto-agile RADIUS. Issues regarding ciper-suite negotiation, legacy interoperability and the potential for biding down attacks, SHOULD be among these discussions. 4.6. Applicability of Automated Key Management Requirements [RFC4107] provides guidelines for when automated key management is necessary. 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 feature Automated Key Management (AKM). The working group determined that AKM was not inherently required for RADIUS based on the following points: o RFC 4107 requires AKM for protocols that involve O(n^2) keys. This does not apply to RADIUS deployments, which require O(n) keys o RADIUS does not require the encryption of large amounts of data in a short time o Organizations already have operational practices to manage existing RADIUS shared secrets to address key changes required through personnel changes Nelson Expires September 3, 2011 [Page 6]
Internet-Draft RADIUS Crypto-Agility Requirements March 2011 o The crypto-agility solution can avoid use cryptographic modes of operation such as a counter mode cipher that require frequent key changes Automated key management is required for RADIUS crypto agility solutions that use cryptographic modes of operation that require frequent key changes. 5. IANA Considerations This document makes no request of IANA. 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. 7. Acknowledgements Thanks to all the reviewers and contributors, inclding Bernard Aboba, Joe Salowey and Glen Zorn. 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, Nelson Expires September 3, 2011 [Page 7]
Internet-Draft RADIUS Crypto-Agility Requirements March 2011 Authorization, and Accounting (AAA) Key Management", BCP 132, RFC 4962, July 2007. Author's Address David B. Nelson Elbrys Networks, Inc. 75 Rochester Avenue, Unit 3 Portsmouth, NH 03801 USA Email: d.b.nelson@comcast.net Nelson Expires September 3, 2011 [Page 8]
