Diameter Attribute-Value Pairs for Cryptographic Key Transport

The Diameter EAP application 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 Extensible Authentication Protocol (EAP) methods (for example, EAP-TLS ). At most one instance of either of these AVPs is allowed in any Diameter message. However, recent work (see, for example, ) 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) 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.

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.

Domain-Specific Root Key . Master Session Key . reauthentication MSK . This is a per-authenticator key, derived from the rRK (below). reauthentication Root Key, derived from the EMSK Extended Master Session Key or DSRK .

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

The Key AVP (AVP Code <AC1>) is of type Grouped. 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-Type > { Keying-Material } [ Key-Lifetime ] [ Key-Name ] [ Key-SPI ] * [ AVP ] ]]>

The Key-Type AVP (AVP Code <AC2>) is of type Enumerated. This AVP identifies the type of the key being sent. The following decimal values are defined in this document: A Domain-Specific Root Key . A reauthentication Root Key . A reauthentication Master Session Key . If additional values are needed, they are to be assigned by IANA according to the policy stated in ,

The Key-Name AVP (AVP Code <AC6>) 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 and for discussions of key name generation in the context of EAP).

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 and is beyond the scope of this document.

The Key-Lifetime AVP (AVP Code <AC4>) is of type Unsigned32 and represents the period of time (in seconds) for which the contents of the Keying-Material AVP () is valid. 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. In addition, client implementations SHOULD check to ensure that the value is reasonable; for example, the lifetime of a key should not generally be longer than the session lifetime (see section 8.13 of .

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.

The security considerations applicable to the Diameter Base Protocol are also applicable to this document, as are those in Section 8.4 of RFC 4072 .

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

Codes must be assigned for the following AVPs using the policy specified in , Section 11.1.1: Key (<AC1>, ) Key-Type (<AC2>, ) Keying-Material (<AC3>, ) Key-Lifetime (<AC4>, ) Key-SPI (<AC5>, ) Key-Name (<AC6>, )

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 (). New values may be assigned for the Key-Type AVP using the "Specification Required" policy ; once values have been assigned, they MUST NOT be deleted, replaced or modified.

Thanks to Niclas Comstedt, Semyon Mizikovsky, Hannes Tschofenig, Joe Salowey, Tom Taylor, Frank Xia, Lionel Morand, Dan Romascanu, Bernard Aboba, Jouni Korhonen and Sebastien Decugis for useful comments, suggestions and review.