Network Working Group G. Zorn Internet-Draft Network Zen Intended status: Informational T. Zhang Expires: September 7, 2009 Advista Technologies J. Walker Intel Corporation J. Salowey Cisco Systems March 6, 2009 Vendor Specific RADIUS Attributes for the Delivery of Keying Material draft-zorn-radius-keywrap-14.txt Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. This document may contain material from IETF Documents or IETF Contributions published or made publicly available before November 10, 2008. The person(s) controlling the copyright in some of this material may not have granted the IETF Trust the right to allow modifications of such material outside the IETF Standards Process. Without obtaining an adequate license from the person(s) controlling the copyright in such materials, this document may not be modified outside the IETF Standards Process, and derivative works of it may not be created outside the IETF Standards Process, except to format it for publication as an RFC or to translate it into languages other than English. 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 7, 2009. Copyright Notice Zorn, et al. Expires September 7, 2009 [Page 1] Internet-Draft RADIUS Keying Material Transfer VSA March 2009 Copyright (c) 2009 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 in effect on the date of publication of this document (http://trustee.ietf.org/license-info). Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Abstract This document defines a set of RADIUS Attributes designed to allow both the secure transmission of cryptographic keying material and strong authentication of any RADIUS message. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Specification of Requirements . . . . . . . . . . . . . . . . 3 3. Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3.1. Keying-Material . . . . . . . . . . . . . . . . . . . . . 4 3.2. MAC-Randomizer . . . . . . . . . . . . . . . . . . . . . . 9 3.3. Message-Authentication-Code . . . . . . . . . . . . . . . 10 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15 5. Security Considerations . . . . . . . . . . . . . . . . . . . 15 6. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 16 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 16 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16 8.1. Normative References . . . . . . . . . . . . . . . . . . . 16 8.2. Informative References . . . . . . . . . . . . . . . . . . 17 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 17 Zorn, et al. Expires September 7, 2009 [Page 2] Internet-Draft RADIUS Keying Material Transfer VSA March 2009 1. Introduction Many remote access deployments (for example, deployments utilizing wireless LAN technology) require the secure transmission of cryptographic keying material from a RADIUS [RFC2865] server to a network access point. Typically, this material is produced as a by- product of an EAP [RFC3748] authentication and is of a form that may be used in virtually any cryptographic algorithm after appropriate processing. This document defines a set of RADIUS Attributes that can be used to securely transfer cryptographic keying material using standard techniques with well understood security properties. In addition, the Message-Authentication-Code Attribute may be used to provide strong authentication for any RADIUS message, including those used for accounting and dynamic authorization. Discussion of this draft may be directed to the authors. 2. Specification of Requirements 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]. 3. Attributes The following subsections describe sub-attributes which are transmitted in one or more RADIUS attributes of type Vendor-Specific [RFC2865]. The Vendor-ID field of the Vendor-Specific Attribute(s) MUST be set to decimal 9 (Cisco). The general format of the attributes is: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type (26) | Length | Vendor ID +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Vendor ID (cont'd) | Sub-type (1)| Sub-length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Value... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Zorn, et al. Expires September 7, 2009 [Page 3] Internet-Draft RADIUS Keying Material Transfer VSA March 2009 Type 26 for vendor specific Length Length of entire attribute including type and length field Vendor ID 4 octets encoding the Cisco Vendor ID of 9 Sub-type Attribute sub-type of 1 Sub-length Length of the sub attribute including the sub-type and sub- length fields Value Value of the sub attribute. This specification concerns the following sub-attributes: o Keying-Material o MAC-Randomizer o Message-Authentication-Code 3.1. Keying-Material Description This Attribute MAY be used to transfer cryptographic keying material from a RADIUS server to a client. It MAY be sent in request messages (e.g., Access-Request, etc.), as well; if the Keying-Material Attribute is present in a request, it SHOULD be taken as a hint by the server that the client prefers this method of key delivery over others, the server is not obligated to honor the hint, however. When the Keying-Material Attribute is included in a request message the Key ID, Lifetime, Zorn, et al. Expires September 7, 2009 [Page 4] Internet-Draft RADIUS Keying Material Transfer VSA March 2009 IV and Key Material fields MAY be omitted. If the client requires the use of the Keying-Material Attribute for keying material delivery and it is not present in the Access- Accept or Access-Challenge message, the client MAY ignore the message in question and end the user session. Any packet that contains a Keying-Material Attribute MUST also include the Message-Authentication-Code Attribute. Any packet that contains an instance of the Keying-Material Attribute MUST NOT contain an instance of any other attribute (e.g., MS-CHAP-MPPE-Keys [RFC2548], Tunnel-Password [RFC2868], etc.) encapsulating identical keying material. The Keying-Material Attribute MUST NOT be used to transfer long- lived keys (i.e., passwords) between RADIUS servers and clients. A summary of the Keying-Material attribute format is shown below. The fields are transmitted from left to right. Zorn, et al. Expires September 7, 2009 [Page 5] Internet-Draft RADIUS Keying Material Transfer VSA March 2009 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type (26) | Length | Vendor ID +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Vendor ID (cont'd) | Sub-type (1)| Sub-length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | String ID ("radius:app-key=") +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ String ID (cont'd) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ String ID (cont'd) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ String ID (cont'd) | Enc Type | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | App ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | KEK ID +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ KEK ID (cont'd) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ KEK ID (cont'd) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ KEK ID (cont'd) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | KM ID +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ KM ID (cont'd) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ KM ID (cont'd) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ KM ID (cont'd) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Lifetime | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IV +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ IV (cont'd) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Data +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type 26 for vendor specific Zorn, et al. Expires September 7, 2009 [Page 6] Internet-Draft RADIUS Keying Material Transfer VSA March 2009 Length Length of entire attribute including type and length field Vendor ID 4 octets encoding the Cisco Vendor ID of 9 Sub-type Attribute sub-type of 1 Sub-length Length of the sub attribute including the sub-type and sub- length fields String-ID The ASCII characters "radius:app-key=" without quotes or null termination. Enc Type The Enc Type field indicates the method used to encrypt the contents of the Data field. This document defines only one value (decimal) for this field: 0 AES Key Wrap with 128-bit KEK [RFC3394] Implementations MUST support Enc Type 0 (AES Key Wrap with 128- bit KEK). Implementation Note A shared secret is used as the key-encrypting-key (KEK) for the AES key wrap algorithm. Implementations SHOULD provide a means to provision a key (cryptographically separate from the normal RADIUS shared secret) to be used exclusively as a KEK. App ID The App ID field is 4 octets in length and identifies the type of application for which the key material is to be used. This allows for multiple keys for different purposes to be present in the same message. This document defines two values for the App ID: Zorn, et al. Expires September 7, 2009 [Page 7] Internet-Draft RADIUS Keying Material Transfer VSA March 2009 0 Unspecified 1 EAP MSK further specification of the content of this field is outside the scope of this document. KEK ID The KEK ID field is 16 octets in length and contains an identifier for the KEK. The KEK ID MUST refer to an encryption key of a type and length appropriate for use with the algorithm specified by the Enc Type field (see above). This key is used to protect the contents of the Data field (below). Further specification of the content of this field is outside the scope of this document. KM ID The KM ID field is 16 octets in length and contains an identifier for the contents of the Data field. The KM ID MAY be used by communicating parties to identify the material being transmitted. The combination of App ID and KM ID MUST uniquely identify the keying material between the parties utilizing it. The KM ID is assumed to be known to the parties that derived the keying material. If the KM ID is not used it is set to 0. Further specification of the content of this field is outside the scope of this document. Lifetime The Lifetime field is an integer [RFC2865] representing the period of time (in seconds) for which the keying material is valid. Note: Applications using this value SHOULD consider the beginning of the lifetime to be the point in time when the keying material is first used. IV The length of the IV field depends upon the value of the Enc Type field, but is fixed for any given value thereof. When the value of the Enc Type field is 0 (decimal), the IV field MUST be 8 octets in length (as illustrated above) and the value of the IV field MUST be as specified in [RFC3394]. Zorn, et al. Expires September 7, 2009 [Page 8] Internet-Draft RADIUS Keying Material Transfer VSA March 2009 Data The Data field is variable length and contains the actual encrypted keying material. 3.2. MAC-Randomizer Description The MAC-Randomizer Attribute MUST be present in any message that includes an instance of the Message-Authentication-Code Attribute. The Random field MUST contain a 32 octet random number which SHOULD satisfy the requirements of [RFC4086]. Implementation Note The Random field MUST be filled in before the MAC is computed. The MAC-Randomizer Attribute SHOULD be placed at the beginning of the RADIUS message if possible. A summary of the MAC-Randomizer attribute format is shown below. The fields are transmitted from left to right. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type (26) | Length | Vendor ID +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Vendor ID (cont'd) | Sub-type (1)| Sub-length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | String ID ("radius:random-nonce=") +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ String ID (cont'd) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ String ID (cont'd) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ String ID (cont'd) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ String ID (cont'd) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Random... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Zorn, et al. Expires September 7, 2009 [Page 9] Internet-Draft RADIUS Keying Material Transfer VSA March 2009 Type 26 for vendor specific Length Length of entire attribute including type and length field Vendor ID 4 octets encoding the Cisco Vendor ID of 9 Sub-type Attribute sub-type of 1 Sub-length Length of the sub attribute including the sub-type and sub- length fields String-ID The ASCII characters "radius:random-nonce=" without quotes or null termination. Random This field MUST contain a 32 octet random number which SHOULD satisfy the requirements of [RFC4086]. 3.3. Message-Authentication-Code Description This Attribute MAY be used to "sign" messages to prevent spoofing. If it is present in a request, the receiver should take this a hint that the sender prefers the use of this Attribute for message authentication; the receiver is not obligated to do so, however. The Message-Authentication-Code Attribute MUST be included in any message that contains a Keying-Material attribute. Any packet that contains an instance of the Message- Authentication-Code Attribute SHOULD NOT contain an instance of the Message-Authenticator Attribute [RFC3579]. If both attributes are to be included in a message (e.g., for backward compatibility in a network containing both old and new clients), the value of Zorn, et al. Expires September 7, 2009 [Page 10] Internet-Draft RADIUS Keying Material Transfer VSA March 2009 the Message-Authentication-Code Attribute MUST be computed first. If any message is received containing an instance of the Message- Authentication-Code Attribute, the receiver MUST calculate the correct value of the Message-Authentication-Code and silently discard the packet if the computed value does not match the value received. If a received message contains an instance of the MAC-Randomizer Attribute (Section 3.2), the received MAC-Randomizer Attribute SHOULD be included in the computation of the Message- Authentication-Code Attribute sent in the response, as described below. A summary of the Message-Authentication-Code attribute format is shown below. The fields are transmitted from left to right. Zorn, et al. Expires September 7, 2009 [Page 11] Internet-Draft RADIUS Keying Material Transfer VSA March 2009 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type (26) | Length | Vendor ID +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Vendor ID (cont'd) | Sub-type (1)| Sub-length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | String ID ("radius:message-authenticator-code=") +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ String ID (cont'd) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ String ID (cont'd) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ String ID (cont'd) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ String ID (cont'd) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ String ID (cont'd) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ String ID (cont'd) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ String ID (cont'd) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ String ID (cont'd) | MAC Type | MAC Key ID +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MAC Key ID (cont'd) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ MAC Key ID (cont'd) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ MAC Key ID (cont'd) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ MAC Key ID (cont'd) | MAC +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MAC (cont'd) ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type 26 for vendor specific Length Length of entire attribute including type and length field Zorn, et al. Expires September 7, 2009 [Page 12] Internet-Draft RADIUS Keying Material Transfer VSA March 2009 Vendor ID 4 octets encoding the Cisco Vendor ID of 9 Sub-type Attribute sub-type of 1 Sub-length Length of the sub attribute including the sub-type and sub- length fields String-ID The ASCII characters "radius:message-authenticator-code=" without quotes or null termination. MAC Type The MAC Type field specifies the algorithm used to create the value in the MAC field. This document defines six values for the MAC Type field: 0 HMAC-SHA-1 [FIPS.180-2.2002] [RFC2104] 1 HMAC-SHA-256 [FIPS.180-2.2002] [RFC4231] 2 HMAC-SHA-512 [FIPS.180-2.2002] [RFC4231] 3 CMAC-AES-128 [NIST.SP800-38B] 4 CMAC-AES-192 [NIST.SP800-38B] 5 CMAC-AES-256 [NIST.SP800-38B] Implementations MUST support MAC Type 0 (HMAC-SHA-1). MAC Key ID The MAC Key ID field is 16 octets in length and contains an identifier for the key. The MAC Key ID MUST refer to a key of a type and length appropriate for use with the algorithm specified by the MAC Type field (see above). Further specification of the content of this field is outside the scope of this document. Zorn, et al. Expires September 7, 2009 [Page 13] Internet-Draft RADIUS Keying Material Transfer VSA March 2009 MAC Both the length and value of the MAC field depend upon the algorithm specified by the value of the MAC Type field. If the algorithm specified is HMAC-SHA-1, HMAC-SHA-256 or HMAC-SHA- 512, the MAC field MUST be 20, 32 or 64 octets in length, respectively. If the algorithm specified is CMAC-AES-128, CMAC-AES-192 or CMAC-AES-256, the MAC field SHOULD be 64 octets in length. The derivation of the MAC field value for all the algorithms specified in this document is identical, except for the algorithm used. There are differences, however, depending upon whether the MAC is being computed for a request message or a response. These differences are detailed below, with the free variable HASH-ALG representing the actual algorithm used. Request Messages For requests (e.g., CoA-Request [RFC5176], Accounting- Request [RFC2866], etc.), the value of the MAC field is a hash of the entire packet except the Request Authenticator in the header of the RADIUS packet, using a shared secret as the key, as follows. MAC = MAC-ALG(Key, Type + Identifier + Length + Attributes) where '+' represents concatenation The MAC-Randomizer Attribute (Section 3.2) MUST be included in any request in which the Message-Authentication-Code Attribute is used. The Random field of the MAC-Randomizer Attribute MUST be filled in before the value of the MAC field is computed. If the Message-Authenticator-Code Attribute is included in a client request, the server SHOULD ignore the contents of the Request Authenticator. Implementation Notes When the hash is calculated, both the MAC field of the Message-Authenticator-Code attribute and the String field of the Message-Authenticator Attribute (if any) MUST be considered to be zero-filled. Implementations SHOULD provide a means to provision a key (cryptographically separate from the normal RADIUS shared secret) to be used exclusively in the generation of the Message-Authentication-Code. Zorn, et al. Expires September 7, 2009 [Page 14] Internet-Draft RADIUS Keying Material Transfer VSA March 2009 Response Messages For responses (e.g., CoA-ACK [RFC5176], Accounting-Response [RFC2866], etc.), the value of the MAC field is a hash of the entire packet except the Response Authenticator in the header of the RADIUS packet using a shared secret as the key, as follows. MAC = HASH-ALG(Key, Type + Identifier + Length + Attributes) where '+ ' represents concatenation If the request contained an instance of the MAC-Randomizer Attribute and the responder wishes to include an instance of the Message-Authentication-Code Attribute in the corresponding response, then the MAC-Randomizer Attribute from the request MUST be included in the response. If the Message-Authenticator-Code Attribute is included in a server response, the client SHOULD ignore the contents of the Response Authenticator. Implementation Notes When the hash is calculated, both the MAC field of the Message-Authenticator-Code attribute and the String field of the Message-Authenticator Attribute (if any) MUST be considered to be zero-filled. The Message-Authentication-Code Attribute MUST be created and inserted in the packet before the Response Authenticator is calculated. Implementations SHOULD provide a means to provision a key (cryptographically separate from the normal RADIUS shared secret) to be used exclusively in the generation of the Message-Authentication-Code. 4. IANA Considerations This document does not define any actions for IANA. 5. Security Considerations It is RECOMMENDED in this memo that two new keys, a key encrypting key and a message authentication key, be shared by the RADIUS client and server. If implemented, these two keys MUST be different from Zorn, et al. Expires September 7, 2009 [Page 15] Internet-Draft RADIUS Keying Material Transfer VSA March 2009 each other and SHOULD NOT be based on a password. These two keys SHOULD be cryptographically independent of the RADIUS shared secret used in calculating the Response Authenticator [RFC2865], Request Authenticator [RFC2866] [RFC5176] and Message-Authenticator Attribute [RFC3579]; otherwise if the shared secret is broken, all is lost. To avoid the possibility of collisions, the same MAC key SHOULD NOT be used with more than 2^(n/2) messages, where 'n' is the length of the MAC value in octets. If a packet that contains an instance of the Keying-Material Attribute also contains an instance of another, weaker key transport attribute (e.g., MS-MPPE-Recv-Key [RFC2548]) encapsulating identical keying material, then breaking the weaker attribute might facilitate a known-plaintext attack against the KEK. 6. Contributors Hao Zhou, Nancy Cam-Winget, Alex Lam, Paul Funk and John Fossaceca all contributed to this document. 7. Acknowledgements Thanks (in no particular order) to Keith McCloghrie, Kaushik Narayan, Murtaza Chiba, Bill Burr, Russ Housley, David McGrew, Pat Calhoun, Joel Halpern, Jim Schaad and Greg Weber for useful feedback. 8. References 8.1. Normative References [FIPS.180-2.2002] National Institute of Standards and Technology, "Secure Hash Standard", FIPS PUB 180-2, August 2002, . [NIST.SP800-38B] Dworkin, M., "Recommendation for Block Cipher Modes of Operation: The CMAC Mode for Authentication", May 2005, . [RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed- Hashing for Message Authentication", RFC 2104, Zorn, et al. Expires September 7, 2009 [Page 16] Internet-Draft RADIUS Keying Material Transfer VSA March 2009 February 1997. [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. [RFC2866] Rigney, C., "RADIUS Accounting", RFC 2866, June 2000. [RFC2868] Zorn, G., Leifer, D., Rubens, A., Shriver, J., Holdrege, M., and I. Goyret, "RADIUS Attributes for Tunnel Protocol Support", RFC 2868, June 2000. [RFC3394] Schaad, J. and R. Housley, "Advanced Encryption Standard (AES) Key Wrap Algorithm", RFC 3394, September 2002. [RFC3579] Aboba, B. and P. Calhoun, "RADIUS (Remote Authentication Dial In User Service) Support For Extensible Authentication Protocol (EAP)", RFC 3579, September 2003. [RFC4086] Eastlake, D., Schiller, J., and S. Crocker, "Randomness Requirements for Security", BCP 106, RFC 4086, June 2005. [RFC4231] Nystrom, M., "Identifiers and Test Vectors for HMAC-SHA- 224, HMAC-SHA-256, HMAC-SHA-384, and HMAC-SHA-512", RFC 4231, December 2005. [RFC5176] Chiba, M., Dommety, G., Eklund, M., Mitton, D., and B. Aboba, "Dynamic Authorization Extensions to Remote Authentication Dial In User Service (RADIUS)", RFC 5176, January 2008. 8.2. Informative References [RFC2548] Zorn, G., "Microsoft Vendor-specific RADIUS Attributes", RFC 2548, March 1999. [RFC3748] Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H. Levkowetz, "Extensible Authentication Protocol (EAP)", RFC 3748, June 2004. Zorn, et al. Expires September 7, 2009 [Page 17] Internet-Draft RADIUS Keying Material Transfer VSA March 2009 Authors' Addresses Glen Zorn Network Zen 1310 East Thomas Street #306 Seattle, Washington 98102 USA Phone: +1 (206) 377-9035 Email: gwz@net-zen.net Tiebing Zhang Advista Technologies 5252 Orange Ave, Suite 108 Cypress, CA 90630 US Phone: +1 (949) 242 0391 Email: tzhang@advistatech.com Jesse Walker Intel Corporation JF3-206 2111 N.E. 25th Ave Hillsboro, OR 97214-5961 US Phone: +1 (503) 712-1849 Email: jesse.walker@intel.com Joseph Salowey Cisco Systems 2901 Third Avenue SEA1/6/ Seattle, WA 98121 US Phone: +1 (206) 256-3380 Email: jsalowey@cisco.com Zorn, et al. Expires September 7, 2009 [Page 18]