The Multimedia Internet Keying (MIKEY) protocol specification 
defines a General Extension payload to allow possible extensions to
MIKEY without having to allocate a new payload type. The General
Extension payload can be used in any MIKEY message and is part of the
authenticated/signed data part. There is an 8-bit type field in that
payload. The type code assignment is IANA-managed, and RFC 3830
requires IETF consensus for assignments from the public range of
The Open Mobile Alliance's (OMA) Browser and Content (BAC) Broadcast
(BCAST) group's Service and Content Protection specification 
specifies the use of a short-term key message (STKM) and a long-term
key message (LTKM) that carry attributes related to Service and
Content protection. Note that any keys associated with the
attributes are part of the MIKEY KEMAC payload. This document
specifies the use of the General Extension payload of MIKEY to carry
the LTKMs or STKMs.
RFC 3830 , the MIKEY General Extension payload defined in , and
the 3rd Generation Partnership Project (3GPP)'s Multimedia Broadcast/
Multicast Service (MBMS) document  specify the transport of MIKEY
messages via unicast or broadcast and the OMA specifications use
either for transport of MIKEY messages.
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 .
OMA BCAST STKM/LTKM MIKEY General Extension: We refer to the General
Extension type -- 5 -- as the OMA BCAST STKM/LTKM MIKEY General
3. MIKEY General Extension for OMA BCAST Usage
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
! Next ! Type ! Length !
! OMA BCAST S/LTKM Subtype (variable length) ~
Figure 1: OMA BCAST MIKEY General Extension
Section 6.1 of RFC 3830 specifies the first three fields of the
General Extension Payload and defines a variable length Data field.
This document specifies the use of Type 5 for OMA BCAST Service and
Content Protection using the Smartcard Profile. The contents of the
variable length data field are defined below.
Subtype: 8 bits. This field indicates the type of the OMA BCAST
payload. In this specification, only two values are specified:
LTKM (1), and STKM (2).
Subtype Specific Data: Variable length. The contents of this field
are defined in Section 6 of the OMA BCAST Service and Content
Protection specification .
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
! Subtype ! Subtype specific data (variable length) ~
Figure 2: STKM/LTKM Subtype Payload4. Interoperability Considerations
This document specifies the use of MIKEY General Extension Payload
Type 5 and a couple of subtype values (1 and 2), one each for OMA
BCAST Service and Content protection's STKM and LTKM payloads.
Interoperability considerations span several standards bodies, with
OMA BCAST 1.0 enabler compliance being the key aspect; as such, it is
up to the OMA test planning to verify the interoperability and
compliance of OMA BCAST 1.0 implementations. This payload type
assignment does not change MIKEY beyond RFC 3830  and RFC 4563
5. Security Considerations
According to RFC 3830, the general extension payload can be used in
any MIKEY message and is part of the authenticated/signed data part.
The parameters proposed to be included in the OMA BCAST MIKEY General
Extension payload (listed in Section 3) need only to be integrity
protected, which is already allowed by the MIKEY specification. The
OMA BCAST MIKEY General Extension Payload SHALL be integrity
protected. Furthermore, keys or any parameters that require
confidentiality MUST NOT be included in the General Extension
Payload. If keys or other confidential data are to be transported
via the General Extension Payload, such data MUST be encrypted and
encapsulated independently. Finally, note that MIKEY already
provides replay protection and that protection covers the General
Extension Payload also.
6. IANA Considerations
IANA has allocated a new General Extension Type from the "General
Extensions payload name spaces" in the IANA registry at
http://www.iana.org/assignments/mikey-payloads for use by OMA BCAST.
Furthermore, IANA maintains a list of corresponding subtypes (0-255)
0 ... Reserved
1 ... LTKM
2 ... STKM
3 ... 191 (maintained by IANA and assigned by IETF Review )
192 ... 255 (Private use)
Many thanks to Jari Arkko, Piron Laurent, and Steffen Fries for their
reviews and suggestions for improvement.
8.1. Normative References
 Arkko, J., Carrara, E., Lindholm, F., Naslund, M., and K.
Norrman, "MIKEY: Multimedia Internet KEYing", RFC 3830,
 Open Mobile Alliance, "Service and Content Protection for Mobile
Broadcast Services", OMA TS-BCAST_SvcCntProtection-V1_0-
20070529-C, 2007, <http://www.openmobilealliance.org/
 Carrara, E., Lehtovirta, V., and K. Norrman, "The Key ID
Information Type for the General Extension Payload in Multimedia
Internet KEYing (MIKEY)", RFC 4563, June 2006.
 3GPP, "3G Security; Security of Multimedia Broadcast/Multicast
Service (MBMS)", 3GPP TS 33.246 6.6.0, March 2006.
 Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
8.2. Informative References
 Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
Considerations Section in RFCs", Work in Progress, March 2007.
Lakshminath Dondeti (editor)
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