Multimedia Internet KEYing (MIKEY) General Extension Payload for Open Mobile Alliance BCAST LTKM/STKM Transport
Extend MIKEY to carry broadcast TV key management parameters for mobile devices.
Dondeti, L., Ed., Castleford, D., and F. Hartung, "Multimedia Internet KEYing (MIKEY) General Extension Payload for Open Mobile Alliance BCAST LTKM/STKM Transport", RFC 4909, DOI 10.17487/RFC4909, June 2007, <https://www.rfc-editor.org/info/rfc4909>.
@misc{rfc4909,
series = {Request for Comments},
number = 4909,
howpublished = {RFC 4909},
publisher = {RFC Editor},
doi = {10.17487/RFC4909},
url = {https://www.rfc-editor.org/info/rfc4909},
author = {L. Dondeti and D. Castleford and F. Hartung},
title = {{Multimedia Internet KEYing (MIKEY) General Extension Payload for Open Mobile Alliance BCAST LTKM/STKM Transport}},
pagetotal = 7,
year = 2007,
month = jun,
} RFC text
Contents
Network Working Group L. Dondeti, Ed.
Request for Comments: 4909 QUALCOMM, Inc.
Category: Informational D. Castleford
France Telecom
F. Hartung
Ericsson Research
June 2007
Multimedia Internet KEYing (MIKEY) General Extension Payload
for Open Mobile Alliance BCAST LTKM/STKM Transport
Status of This Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Copyright Notice
Copyright (C) The IETF Trust (2007).
Abstract
This document specifies a new Multimedia Internet KEYing (MIKEY)
General Extension payload (RFC 3830) to transport the short-term key
message (STKM) and long-term key message (LTKM) payloads defined in
the Open Mobile Alliance's (OMA) Browser and Content (BAC) Broadcast
(BCAST) group's Service and Content protection specification.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 2
3. MIKEY General Extension for OMA BCAST Usage . . . . . . . . . . 3
4. Interoperability Considerations . . . . . . . . . . . . . . . . 3
5. Security Considerations . . . . . . . . . . . . . . . . . . . . 4
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 4
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 4
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 5
8.1. Normative References . . . . . . . . . . . . . . . . . . . 5
8.2. Informative References . . . . . . . . . . . . . . . . . . 5
1. Introduction
The Multimedia Internet Keying (MIKEY) protocol specification [1]
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
0-240.
The Open Mobile Alliance's (OMA) Browser and Content (BAC) Broadcast
(BCAST) group's Service and Content Protection specification [2]
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 [1], the MIKEY General Extension payload defined in [3], and
the 3rd Generation Partnership Project (3GPP)'s Multimedia Broadcast/
Multicast Service (MBMS) document [4] specify the transport of MIKEY
messages via unicast or broadcast and the OMA specifications use
either for transport of MIKEY messages.
2. Terminology
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 [5].
OMA BCAST STKM/LTKM MIKEY General Extension: We refer to the General
Extension type -- 5 -- as the OMA BCAST STKM/LTKM MIKEY General
Extension .
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 [2].
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 Payload
4. 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 [1] and RFC 4563
[3].
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)
as follows:
0 ... Reserved
1 ... LTKM
2 ... STKM
3 ... 191 (maintained by IANA and assigned by IETF Review [6])
192 ... 255 (Private use)
7. Acknowledgments
Many thanks to Jari Arkko, Piron Laurent, and Steffen Fries for their
reviews and suggestions for improvement.
8. References
8.1. Normative References
[1] Arkko, J., Carrara, E., Lindholm, F., Naslund, M., and K.
Norrman, "MIKEY: Multimedia Internet KEYing", RFC 3830,
August 2004.
[2] Open Mobile Alliance, "Service and Content Protection for Mobile
Broadcast Services", OMA TS-BCAST_SvcCntProtection-V1_0-
20070529-C, 2007, <http://www.openmobilealliance.org/
release_program/bcast_v1_0.html>.
[3] 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.
[4] 3GPP, "3G Security; Security of Multimedia Broadcast/Multicast
Service (MBMS)", 3GPP TS 33.246 6.6.0, March 2006.
[5] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
8.2. Informative References
[6] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
Considerations Section in RFCs", Work in Progress, March 2007.
Authors' Addresses
Lakshminath Dondeti (editor)
QUALCOMM, Inc.
5775 Morehouse Dr
San Diego, CA
USA
Phone: +1 858-845-1267
EMail: ldondeti@qualcomm.com
David Castleford
France Telecom
4, rue du Clos Courtel
35512 Cesson Sevigne Cedex,
France
Phone: + 33 (0)2 99 12 49 27
EMail: david.castleford@orange-ftgroup.com
Frank Hartung
Ericsson Research
Ericsson Allee 1
52134 Herzogenrath,
Germany
Phone: +49 2407 575389
EMail: frank.hartung@ericsson.com
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AI ELI5
On this page
§1Extending MIKEY for Broadcast
MIKEY is a key agreement and key transport protocol that defines a General Extension payload to allow extensions without needing a new protocol. MIKEY is used in mobile networks, including 3GPP broadcast services and the Open Mobile Alliance's broadcast specifications. The OMA BCAST Service and Content Protection specification defines two payloads: the Short-Term Key Message (STKM) and the Long-Term Key Message (LTKM), which carry service protection attributes. These payloads need to be transported in MIKEY messages.
This document specifies how to carry STKM and LTKM payloads inside a MIKEY General Extension payload, allowing broadcast receivers to obtain the necessary key material and service protection information in a single key distribution exchange.
MIKEY is how phones get secret keys. OMA BCAST is how broadcast TV works. This document shows how to put broadcast TV key information into MIKEY messages.
§2The General Extension Mechanism
RFC 3830 (the MIKEY specification) defines a General Extension payload that can be used in any MIKEY message to carry arbitrary extension data. The General Extension payload is part of the authenticated or signed data in MIKEY messages, meaning it is integrity protected. Each General Extension carries an 8-bit Type field that identifies the extension type, and a variable-length Data field containing the extension-specific content.
This RFC specifies the use of General Extension Type 5 for OMA BCAST service and content protection. Type 5 carries a Subtype field (8 bits) that distinguishes between different payloads. The LTKM (long-term key message) is subtype 1, and the STKM (short-term key message) is subtype 2. The remainder of the extension is subtype-specific data as defined in the OMA specification. This allows a single MIKEY extension to carry either LTKM or STKM payloads depending on the subtype value.
MIKEY has a slot for extra information. This takes that slot (number 5) and puts broadcast key info inside using subtypes: 1 for long-term keys, 2 for short-term keys.
§3Broadcast Key Management and Protection
The LTKM and STKM payloads defined in the OMA BCAST specification carry attributes related to service and content protection, such as encryption algorithms, authentication methods, and key usage policies. Note that the actual encryption keys themselves are not carried in the General Extension payload. Keys are instead encrypted and transported in the MIKEY KEMAC payload, which provides confidentiality for sensitive key material.
When a broadcast receiver initiates a MIKEY key exchange to obtain broadcast content protection keys, the server can include a General Extension payload (Type 5) containing either an LTKM or STKM subtype. The receiver extracts the protection attributes from the extension and the encrypted keys from the KEMAC payload. The MIKEY message provides both authentication of the key material and replay protection, ensuring the broadcast receiver obtains legitimate, non-replayed key information for accessing protected content.
The extension carries rules like "use this encryption" and "check this way." The actual keys go elsewhere, encrypted. Together they tell the phone how to decrypt the broadcast.
§4Security and Interoperability
The General Extension payload is always part of the authenticated or signed data in MIKEY messages, so the LTKM and STKM parameters carried in the extension are always integrity protected. Keys or confidential data MUST NOT be included in the General Extension payload itself; any secret material must be encrypted separately. The specification requires that the General Extension payload be integrity protected and that replay protection, which MIKEY provides, covers the extension as well. Interoperability is ensured through the IANA registry, which manages the assignment of General Extension types and subtypes. OMA BCAST 1.0 implementations must comply with the assignment of Type 5 and subtypes 1 and 2 defined in this document.
The information in the extension is always checked to make sure it has not been tampered with. Secret keys never go in the extension—they go elsewhere, encrypted. Phones and servers that follow this spec will work together.