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)

Status of this Memo

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   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",
   document are to be interpreted as described in [RFC2119].

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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

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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

   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.

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   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,

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   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

   Included in negotiation techniques are "hint and consent" mechanisms
   where the NAS provides a list of algorithms and the server selects

   Proposals MUST support replay protection.  The existing mechanisms
   for replay protection are considered adequate and should be

   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

   Crypto-agility solutions MUST be interoperable between independent
   implementations based purely on the information provided in the

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

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   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

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

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7.  Acknowledgements


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

   Phone: +1.603.570.2636

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