Request to review Media Type */rtp-enc-aescm128 for 3GPP

[Magnus Westerlund]

Hi,

The following Media Type was discussed on the list at the end of 2004. 
Time to finally register it. I intend to request IESG to approve 
registration following the SDO rules on the 6th of October. So if 
someone has strong objections against this speak up before then.

The filled in registration template is from 3GPP TS 26.234 V.6.8.0:
http://www.3gpp.org/ftp/Specs/archive/26_series/26.234/26234-680.zip

K.1.4.1	MIME type definition

MIME media type name: audio, video, text

MIME subtype name: rtp-enc-aescm128

Required parameters:
opt: 	The payload type number of the payload type contained in the 
encrypted payload. An integer value between 0-127.
rate: 	The timestamp rate of this payload type, which shall be the same 
as that of the original payload type. This is an integer value between 1 
and 2^32.

ContentID: 	The OMA DRM content ID [75] used to identify the content 
when establishing a crypto context. The value is an RFC 2396 [60] URI, 
which shall be quoted using <">.

RightsIssuerURL: 	The right issuer URL as defined by OMA DRM [75]. The 
value is an URI in accordance with RFC 2396 [60], which shall be quoted 
using <">.

IVnonce: The value of this parameter is the nonce that forms the IV as 
specified by the crypto transform, encoded using Base 64 [69].

Optional parameters:

SelectiveEncryption: 	Indicates if this stream is selectively encrypted. 
Allowed values are 0 (false) and 1 (true). If not present, selective 
encryption shall not be used. Please note that unless this indicator is 
integrity protected, it fulfills no purpose.

Encoding considerations:
This type is only defined for transfer via RTP (RFC 3550).

Security considerations:
See considerations raised in RTP RFC 3550 [9] and any applicable profile 
like RFC 3551 [10] or RFC 3711 [72]. Further see 3GPP TS 26.234, Release 
6, Annex K for comments on security issues. The main issues that exists are:
-	This RTP payload format only confidentiality protects the RTP payload, 
thus header information is leaked, similarly to SRTP.

-	The use of stream ciphers as AES CM and no integrity protection allows 
an attacker to purposefully attack the content of the encrypted RTP 
payload by switching individual bits.

-	The usage of selective encryption without integrity protection allows 
for an attacker to perform any replacements of complete RTP payloads and 
packets it desires.

-	The payload format makes the receiver vulnerable to denial of service 
attacks that inserts RTP packets into the stream, that the receiver then 
interprets as being encrypted thus wasting computational resources. To 
prevent this attack, authentication needs to be used.
Interoperability considerations:

Published specification:
3GPP TS 26.234, Release 6.
Open Mobile Alliance DRM Content Format V2.0

Applications which use this media type:
Third Generation Partnership Project (3GPP) Packet-switched Streaming 
Service (PSS) clients and servers, which supports the Open Mobile 
Alliance's specification of Digital Rights Management version 2.0.

Additional information:

Magic number(s): N/A

File extension(s): N/A

Macintosh File Type Code(s): N/A

Person & email address to contact for further information:
	magnus.westerlund at ericsson.com

Intended usage:
Common

Author/Change controller:

3GPP TSG SA

-- 

Magnus Westerlund

Multimedia Technologies, Ericsson Research EAB/TVA/A
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