Internet Engineering Task Force Carrara, Lehtovirta, Norrman
(Ericsson)
INTERNET-DRAFT
EXPIRES: April 2005 October 2004
The Key ID Information Type for the General Extension Payload in MIKEY
<draft-carrara-newtype-keyid-00.txt>
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Abstract
This memo specifies a new Type (the Key ID Information Type) for the
General Extension Payload in the Multimedia Internet KEYing
Protocol. This is used in the Multimedia Broadcast/Multicast Service
specified in the 3rd Generation Partnership Project.
INTERNET-DRAFT newtype-keyid October, 2004
TABLE OF CONTENTS
1. Introduction...................................................2
2. The MBMS key management........................................2
3. The Key ID Information Type for the General Extension Payload..3
4. Security Considerations........................................5
5. IANA Considerations............................................5
6. Acknowledgements...............................................5
7. Author's Addresses.............................................5
8. References.....................................................6
1. Introduction
The 3rd Generation Partnership Project (3GPP) is currently involved
in the development of a multicast and broadcast service, the
Multimedia Broadcast/Multicast Service (MBMS), and its security
architecture [MBMS]. This service is specified for 3GPP Release 6.
[MBMS] requires the use of the Multimedia Internet KEYing (MIKEY)
Protocol [RFC3830], to convey the keys and related security
parameters needed to secure the media that is multicast or
broadcast. For the streaming scenario, the security protocol used to
protect the media is the Secure Real-time Transport Protocol (SRTP)
[RFC3711].
One of the requirements that MBMS puts on security is the
possibility to perform frequent updates of the keys. The rationale
behind this is that it should be inconvenient for subscribers to
publish the decryption keys enabling non-subscribers to view the
content. To implement this, MBMS uses a three level key management,
to distribute group keys to the clients, and be able to re-key by
pushing down a new group key. As illustrated in the section below,
MBMS has the need to identify which types of key are involved in the
MIKEY message, and their identity.
This memo specifies a new Type for the General Extension Payload in
MIKEY, to identify the type and identity of involved keys.
2. The MBMS key management
The key management solution adopted by MBMS uses a three level key
management. The keys are used in the way described below. "Clients"
refers to the clients who have subscribed to a given
multicast/broadcast service.
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-
the User Key (MUK), one point-to-point key between the multicast
server and each client
-
the Service Key (MSK), one group key between the multicast server
and all the clients
-
the Traffic Key (MTK), one group traffic key between the multicast
server and all clients.
The Traffic Keys are the keys that are regularly updated.
The point-to-point MUK key (first-level key) is shared between the
multicast server and the client via means defined by MBMS [MBMS].
The MUK is used as pre-shared key to run MIKEY with the pre-shared
key method [RFC3830], to deliver (point-to-point) the MSK key. The
same MSK key is pushed to all the clients, to be used as a (second-
level) group key.
Then, the MSK is used to push to all the clients an MTK key (third-
level key), the actual group key that is used for the protection of
the media traffic. The MTK is, in other words, the master key for
SRTP in the streaming case.
To allow this distribution, an indication of the type and identity
of involved keys in the MIKEY message is needed. This indication is
carried in a new Type of the General Extension Payload in MIKEY.
3. The Key ID Information Type for the General Extension Payload
The General Extension payload in MIKEY is defined in Section 6.15 of
[RFC3830].
The Key ID Information Type (Type 2) formats the General Extension
payload as follows:
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 payload ! Type ! Length !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! Key ID Information ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Next Payload and Length are defined in Section 6.15 of [RFC3830].
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* Type (8 bits): identifies the type of the General Payload
[RFC3830]. This memo adds Type 2 to the ones already defined in
[RFC3830].
Type | Value | Comments
------------------------------------------------------------
keyid | 2 | information on type and identity of keys
Table 1.
* Key ID Information (variable length): the general payload data
transporting the type and identifier of a key. This field is formed
by Key Type ID sub-payloads as specified below.
The Key Type ID sub-payload is formatted as follows:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! Key Type ! Key ID Length ! Key ID ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
* Key Type (8 bits): describes the type of the key. Predefined
types are listed in Table 2.
Key Type | Value | Comment
--------------------------------------
MBMS User Key | 0 | User key (point-to-point)
MBMS Service Key | 1 | Group key
MBMS Transport Key | 2 | Group traffic key
Table 2.
* Key ID Length (8 bits): describes the length of the Key ID
field in bytes.
* Key ID (variable length): defines the identity of the key.
Note that there may be more than one Key Type ID sub-payload in an
extension, and that the overall length of the Key Identifier ID
field cannot exceed 2^16 bytes.
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4. Security Considerations
This memo is not foreseen to introduce security implications. For
the security considerations of the MIKEY protocol, see [RFC3830].
5. IANA Considerations
A new MIKEY General Extension Payload Type needs to be registered
for this purpose. The registered value is requested to be 2
according to Section 3.
The name spaces for the following fields in the General Extensions
payload (from Section 3) are requested to be managed by IANA:
* Key Type (Table 2).
6. Acknowledgements
We would like to thank Fredrik Lindholm.
7. Author's Addresses
Questions and comments should be directed to the authors:
Elisabetta Carrara
Ericsson Research
SE-16480 Stockholm Phone: +46 8 50877040
Sweden EMail: elisabetta.carrara@ericsson.com
Vesa Lehtovirta
Ericsson Research
02420 Jorvas Phone: +358 9 2993314
Finland EMail: vesa.lehtovirta@ericsson.com
Karl Norrman
Ericsson Research
SE-16480 Stockholm Phone: +46 8 4044502
Sweden EMail: karl.norrman@ericsson.com
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8. References
Normative
[MBMS] 3GPP TS 33.246 V6.0.0 (2004-09), Technical Specification 3rd
Generation Partnership Project; Technical Specification Group
Services and System Aspects; Security; Security of Multimedia
Broadcast/Multicast Service (Release 6)
[RFC3830] Arkko et al., "MIKEY: Multimedia Internet KEYing", RFC
3830, August 2004.
Informative
[RFC3711] Baugher et al., "The Secure Real-time Transport Protocol
(SRTP)", RFC3711, March 2004.
Copyright Notice
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This draft expires in April 2005.
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