Internet Engineering Task Force Carrara, Lehtovirta, Norrman
(Ericsson)
INTERNET-DRAFT
EXPIRES: June 2005 December 2004
The Key ID Information Type for the General Extension Payload in MIKEY
<draft-ietf-msec-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, e.g., the Multimedia Broadcast/Multicast
Service specified in the 3rd Generation Partnership Project.
INTERNET-DRAFT newtype-keyid December, 2004
TABLE OF CONTENTS
1. Introduction...................................................2
2. Rationale......................................................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].
[MBMS] requires the use of the Multimedia Internet KEYing (MIKEY)
Protocol [RFC3830], to convey the keys and related security
parameters needed to secure the multimedia that is multicast or
broadcast.
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. Rationale
An application where this extension is used is 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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û the MBMS User Key (MUK), point-to-point key between the multicast
server and each client
û the MBMS Service Key (MSK), group key between the multicast server
and all the clients
û the MBMS Traffic Key (MTK), 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. For example, the MTK could be the master key for
SRTP [3711] in the streaming case.
A Key Domain identifier defines the domain where the group keys are
valid or applicable. For example it may define a specific service
provider.
To allow the key distribution described above, 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 3) formats the General Extension
payload as follows:
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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].
* Type (8 bits): identifies the type of the General Payload
[RFC3830]. This memo adds Type 3 to the ones already defined in
[RFC3830].
Type | Value | Comments
------------------------------------------------------------
Key ID | 3 | 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 ID Type sub-payloads as specified below.
The Key ID Type sub-payload is formatted as follows:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! Key ID Type ! Key ID Length ! Key ID ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
* Key ID Type (8 bits): describes the type of the key ID.
Predefined types are listed in Table 2.
Key ID Type | Value | Comment
--------------------------------------
MBMS Key Domain ID | 0 | ID of the group key domain
MBMS Service Key ID | 1 | ID of the group key
MBMS Transport Key ID | 2 | ID of the group traffic key
Table 2.
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* 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 ID Type sub-payload in an
extension, and that the overall length (i.e., the sum of lengths of
all Key ID Type sub-payloads) of the Key ID information field cannot
exceed 2^16 bytes. Applications using this general extension payload
have to define the semantics and usage of the Key ID Type sub-
payloads.
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 3
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 ID 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
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Finland EMail: vesa.lehtovirta@ericsson.com
Karl Norrman
Ericsson Research
SE-16480 Stockholm Phone: +46 8 4044502
Sweden EMail: karl.norrman@ericsson.com
8. References
Normative
[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.
[MBMS] 3GPP TS 33.246, Technical Specification 3rd Generation
Partnership Project; Technical Specification Group Services and
System Aspects; Security; Security of Multimedia Broadcast/Multicast
Service.
Copyright Notice
Copyright (C) The Internet Society (2004). This document is subject
to the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights.
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This draft expires in June 2005.
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