Diameter Attribute-Value Pairs for Cryptographic Key Transport
draft-ietf-dime-local-keytran-06

Abstract

Some Authentication, Authorization, and Accounting (AAA) applications require the transport of cryptographic keying material; this document specifies a set of Attribute-Value Pairs (AVPs) providing native Diameter support of cryptographic key delivery.

Status of this Memo

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Table of Contents

1.  Introduction
2.  Terminology
    2.1.  Standards Language
    2.2.  Technical Terms and Acronyms
3.  Attribute-Value Pair Definitions
    3.1.  Key AVP
        3.1.1.  Key-Type AVP
        3.1.2.  Key-Name AVP
        3.1.3.  Keying-Material AVP
        3.1.4.  Key-Lifetime AVP
        3.1.5.  Key-SPI
4.  Security Considerations
5.  IANA Considerations
    5.1.  AVP Codes
    5.2.  AVP Values
6.  Acknowledgements
7.  References
    7.1.  Normative References
    7.2.  Informative References
§  Authors' Addresses

1.  Introduction

The Diameter EAP application (Eronen, P., Hiller, T., and G. Zorn, “Diameter Extensible Authentication Protocol (EAP) Application,” August 2005.) [RFC4072] defines the EAP-Master-Session-Key and EAP-Key-Name AVPs for the purpose of transporting cryptographic keying material derived during the execution of certain The Extensible Authentication Protocol (EAP) [RFC3748] (Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H. Levkowetz, “Extensible Authentication Protocol (EAP),” June 2004.) methods (for example, EAP-TLS [RFC5216] (Simon, D., Aboba, B., and R. Hurst, “The EAP-TLS Authentication Protocol,” March 2008.)). At most one instance of either of these AVPs is allowed in any Diameter message.

However, recent work (see, for example, [RFC5295] (Salowey, J., Dondeti, L., Narayanan, V., and M. Nakhjiri, “Specification for the Derivation of Root Keys from an Extended Master Session Key (EMSK),” August 2008.)) has specified methods to derive other keys from the keying material created during EAP method execution that may require transport in addition to the MSK. In addition, the EAP Re-authentication Protocol (ERP) [RFC5296] (Narayanan, V. and L. Dondeti, “EAP Extensions for EAP Re-authentication Protocol (ERP),” August 2008.) specifies new keys that may need to be transported between Diameter nodes.

This note specifies a set of AVPs allowing the transport of multiple cryptographic keys in a single Diameter message.

2.  Terminology

2.1.  Standards 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 RFC 2119 (Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” March 1997.) [RFC2119].

2.2.  Technical Terms and Acronyms

DSRK

Domain-Specific Root Key [RFC5295] (Salowey, J., Dondeti, L., Narayanan, V., and M. Nakhjiri, “Specification for the Derivation of Root Keys from an Extended Master Session Key (EMSK),” August 2008.).

MSK

Master Session Key [RFC3748] (Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H. Levkowetz, “Extensible Authentication Protocol (EAP),” June 2004.).

rMSK

reauthentication MSK [RFC5296] (Narayanan, V. and L. Dondeti, “EAP Extensions for EAP Re-authentication Protocol (ERP),” August 2008.). This is a per-authenticator key, derived from the rRK (below).

rRK

reauthentication Root Key, derived from the EMSK Extended Master Session Key [RFC3748] (Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H. Levkowetz, “Extensible Authentication Protocol (EAP),” June 2004.) or DSRK [RFC5296] (Narayanan, V. and L. Dondeti, “EAP Extensions for EAP Re-authentication Protocol (ERP),” August 2008.).

3.  Attribute-Value Pair Definitions

This section defines new AVPs for the transport of cryptographic keys in the Diameter EAP application [RFC4072], as well as other Diameter applications.

3.1.  Key AVP

The Key AVP (AVP Code <AC1>) is of type Grouped [RFC3588] (Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J. Arkko, “Diameter Base Protocol,” September 2003.). It contains the type and keying material and, optionally, an indication of the usable lifetime of the key, the name of the key and a Security Parameter Index (SPI) with which the key is associated.

Key ::= < AVP Header: AC1 >
          < Key-Type >
          { Keying-Material }
          [ Key-Lifetime ]
          [ Key-Name ]
          [ Key-SPI ]
        * [ AVP ]

3.1.1.  Key-Type AVP

The Key-Type AVP (AVP Code <AC2>) is of type Enumerated and signifies the type of the key being sent. The following decimal values are defined in this document:

MSK (0)

The EAP Master Session Key [RFC3748] (Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H. Levkowetz, “Extensible Authentication Protocol (EAP),” June 2004.)

DSRK (1)

A Domain-Specific Root Key [RFC5295] (Salowey, J., Dondeti, L., Narayanan, V., and M. Nakhjiri, “Specification for the Derivation of Root Keys from an Extended Master Session Key (EMSK),” August 2008.).

rRK (2)

A reauthentication Root Key [RFC5296] (Narayanan, V. and L. Dondeti, “EAP Extensions for EAP Re-authentication Protocol (ERP),” August 2008.).

rMSK (3)

A reauthentication Master Session Key [RFC5296] (Narayanan, V. and L. Dondeti, “EAP Extensions for EAP Re-authentication Protocol (ERP),” August 2008.).

IKEv2-PSK (4)

A pre-shared key for use in IKE-V2 key exchange [I‑D.ietf‑dime‑ikev2‑psk‑diameter] (Cakulev, V. and A. Lior, “Diameter IKEv2 PSK: Pre-Shared Secret-based Support for IKEv2 Server to Diameter Server Interaction,” March 2010.).

If additional values are needed, they are to be assigned by IANA according to the policy stated in Section 5.2 (AVP Values)

3.1.2.  Key-Name AVP

The Key-Name AVP is of type OctetString. It contains an opaque key identifier. Exactly how this name is generated and used depends on the key type and usage in question, and is beyond the scope of this document (see [RFC5247] (Aboba, B., Simon, D., and P. Eronen, “Extensible Authentication Protocol (EAP) Key Management Framework,” August 2008.) and [RFC5295] (Salowey, J., Dondeti, L., Narayanan, V., and M. Nakhjiri, “Specification for the Derivation of Root Keys from an Extended Master Session Key (EMSK),” August 2008.) for discussions of key name generation in the context of EAP).

3.1.3.  Keying-Material AVP

The Keying-Material AVP (AVP Code <AC3>) is of type OctetString. The exact usage of this keying material depends upon several factors, including the link layer in use and the type of the key; it is beyond the scope of this document.

3.1.4.  Key-Lifetime AVP

The Key-Lifetime AVP (AVP Code <AC4>) is of type Integer64 [RFC3588] (Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J. Arkko, “Diameter Base Protocol,” September 2003.) and represents the period of time (in seconds) for which the contents of the Keying-Material AVP (Section 3.1.3 (Keying-Material AVP)) is valid.

NOTE:

Applications using this value SHOULD consider the beginning of the lifetime to be the point in time when the message containing the keying material is received.

3.1.5.  Key-SPI

The Key-SPI AVP (AVP Code <AC5>) is of type Unsigned32 and contains a SPI value that can be used with other parameters for identifying associated keying material.

4.  Security Considerations

The security considerations applicable to the Diameter Base Protocol [RFC3588] (Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J. Arkko, “Diameter Base Protocol,” September 2003.) are also applicable to this document, as are those in Section 8.4 of RFC 4072 [RFC4072] (Eronen, P., Hiller, T., and G. Zorn, “Diameter Extensible Authentication Protocol (EAP) Application,” August 2005.).

5.  IANA Considerations

Upon publication of this memo as an RFC, IANA is requested to assign values as described in the following sections.

5.1.  AVP Codes

Codes must be assigned for the following AVPs using the policy specified in RFC 3588, Section 11.1.1:

• Key (<AC1>, Section 3.1 (Key AVP))
• Key-Type (<AC2>, Section 3.1.1 (Key-Type AVP))
• Keying-Material (<AC3>, Section 3.1.3 (Keying-Material AVP))
• Key-Lifetime (<AC4>, Section 3.1.4 (Key-Lifetime AVP))
• Key-SPI (<AC5>, Section 3.1.5 (Key-SPI))

5.2.  AVP Values

IANA is requested to create a new registry for values assigned to the Key-Type AVP and populated with the decimal values defined in this document (Section 3.1.1 (Key-Type AVP)). New values may be assigned for the Key-Type AVP using the "Expert Review" policy [RFC5226] (Narten, T. and H. Alvestrand, “Guidelines for Writing an IANA Considerations Section in RFCs,” May 2008.); once values have been assigned, they MUST NOT be deleted, replaced, modified or deprecated.

6.  Acknowledgements

Thanks to Semyon Mizikovsky, Hannes Tschofenig, Joe Salowey, Tom Taylor, Frank Xia and Sebastien Decugis for useful comments.

7.  References

7.1. Normative References

7.2. Informative References

Authors' Addresses