Session Description Protocol (SDP) Attributes for OMA BCAST Service and Content Protection
draft-dondeti-oma-mmusic-sdp-attrs-00

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Abstract

This document provides descriptions of SDP attributes used by the Open Mobile Alliance's Broadcast Service and Content Protection specification.

Table of Contents

1.  Introduction
2.  Terminology
3.  New SDP Attributes
4.  Security Considerations
5.  IANA Considerations
    5.1.  Registration of new SDP attributes
        5.1.1.  Registration of the attribute bcastversion:<major>.<minor>
        5.1.2.  Registration of the attribute stkmstream:<id of the stkm stream>
        5.1.3.  Registration of the attribute SRTPAuthentication:<id for SRTP authentication algorithm value>
        5.1.4.  Registration of the attribute SRTPROCTxRate:<ROC transmission rate>
6.  Acknowledgments
7.  References
    7.1.  Normative References
    7.2.  Informative References
§  Authors' Addresses
§  Intellectual Property and Copyright Statements

1.  Introduction

The Open Mobile Alliance (OMA)'s Broadcast (BCAST) group is specifying service and content protection mechanisms for broadcast services over wireless networks. As part of that specification, several new SDP attributes are necessary to allow the broadcast server to signal the service and content protection parameters to clients.

Section 8.2.4 of RFC 4566 [1] (Handley, M., Jacobson, V., and C. Perkins, “SDP: Session Description Protocol,” July 2006.) requires that new SDP attributes are registered through IANA with name, contact information and description (and other similar parameters). A standards track specification is RECOMMENDED if the new attribute(s) will have widespread use and interoperability considerations.

OMA BCAST specifications are expected to be used by 3GPP MBMS, 3GPP2 BCMCS and DVB-H based broadcast wireless systems.

This document provides descriptions of the SDP attributes used in the OMA BCAST Service and Content Protection specification [2] (Open Mobile Alliance, “Service and Content Protection for Mobile Broadcast Services,” 2007.).

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 [3] (Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” March 1997.).

3.  New SDP Attributes

The following new SDP attributes have been specified:

• a=bcastversion:<major>.<minor>
• a=stkmstream:<id of the stkm stream>
• a=SRTPAuthentication:<id for SRTP authentication algorithm value>
• a=SRTPROCTxRate:<ROC transmission rate>

See Section 5 for details on IANA considerations.

4.  Security Considerations

In addition to the notes in Section 7 of RFC 4566 [1] (Handley, M., Jacobson, V., and C. Perkins, “SDP: Session Description Protocol,” July 2006.), the following considerations may be applicable:

The bcastversion parameter indicates the version of the broadcast system used for distribution of broadcast content. In case future versions indicated by this parameter allow for enhanced or additional security features, the bcastversion parameter, if unprotected, could be utilized for downgrade attacks.

The stkmstream parameter provides references to relevant key management streams so that receivers can map the media streams to key streams and retrieve the necessary keys to decrypt media. As such, this parameter could be utilized, if unprotected, for DoS attacks.

5.  IANA Considerations

This document, following the guidelines of [5] (Narten, T. and H. Alvestrand, “Guidelines for Writing an IANA Considerations Section in RFCs,” October 1998.), instructs IANA to register a number of SDP attributes.

5.1.  Registration of new SDP attributes

This memo provides instructions to IANA to register a number of OMA BCAST only attributes in the Session Description Protocol Parameters registry [1] (Handley, M., Jacobson, V., and C. Perkins, “SDP: Session Description Protocol,” July 2006.). The registration data, according to RFC 4566 [1] (Handley, M., Jacobson, V., and C. Perkins, “SDP: Session Description Protocol,” July 2006.) follows.

The registration templates below refer to the OMA-TS-BCAST_SvcCntProtection specification [2] (Open Mobile Alliance, “Service and Content Protection for Mobile Broadcast Services,” 2007.).

5.1.1.  Registration of the attribute bcastversion:<major>.<minor>

Contact:

Anja Jerichow <anja.jerichow@nsn.com>

Phone:

+49 89 636-45868

Attribute name:

bcastversion

Long-form attribute name:

BCAST version

Type of attribute:

session-level

This attribute is not dependent on charset.

Purpose:

This attribute specifies the OMA BCAST version "bcastversion" value in the format x.y.

Specification of attribute values:

This attribute has a mandatory value of the form <major>.<minor>, where <major> and <minor> are non-negative decimal numbers. The att-value field is of XML data type decimal. For details, see OMA-TS-BCAST_SvcCntProtection, Section 10.1.1.

5.1.2.  Registration of the attribute stkmstream:<id of the stkm stream>

Contact:

Anja Jerichow <anja.jerichow@nsn.com>

Phone:

+49 89 636-45868

Attribute name:

stkmstream

Long-form attribute name:

Short Term Key Message stream identifyer

Type of attribute:

session-level or media-level

The attribute can be at session level, in which case it applies to all media streams, or it can be at media level, in which case it only applies to the specified media and would overwrite possible session level attributes.

This attribute is not dependent on charset.

Purpose:

The stkmstream attribute specifies the mapping of Short Term Key Message streams to media streams in the SDP.

Each session or media stream can have multiple stkmstream attributes. By comparing the value of this attribute with the identifier of each STKM stream, the terminal can figure out which one to listen to and process. We note that this attribute is optional and hence would not be there for unencrypted media streams.

Specification of attribute values:

This attribute has a mandatory value of the form <id of the stkm stream>, a unique non-zero integer identifying a particular key stream. Numbers are unique within a particular SDP session i.e. no global numbering is required. The att-value field is of XML data type unsignedShort. For details, see OMA-TS-BCAST_SvcCntProtection, Section 10.1.3

5.1.3.  Registration of the attribute SRTPAuthentication:<id for SRTP authentication algorithm value>

Contact:

Anja Jerichow <anja.jerichow@nsn.com>

Phone:

+49 89 636-45868

Attribute name:

SRTPAuthentication

Long-form attribute name:

SRTP authentication algorithm value identifyer

Type of attribute:

media-level

This attribute is not dependent on charset.

Purpose:

When SRTP is used, the attribute SRTPAuthentication states which authentication algorithm to use.

Specification of attribute values:

Based on [4] (Lehtovirta, V., Naslund, M., and K. Norrman, “Integrity Transform Carrying Roll-Over Counter for the Secure Real-time Transport Protocol (SRTP),” January 2007.), the identifier is a transform-independent parameter of the cryptographic context for SRTP in integer format.

One of the following three integrity transforms registered for the three modes MUST be used: value "2" for RCCm1, "3" for RCCm2 and "4" for RCCm3. For details, see OMA-TS-BCAST_SvcCntProtection, Section 10.4.

5.1.4.  Registration of the attribute SRTPROCTxRate:<ROC transmission rate>

Contact:

Anja Jerichow <anja.jerichow@nsn.com>

Phone:

+49 89 636-45868

Attribute name:

SRTPROCTxRate

Long-form attribute name:

ROC transmission rate

Type of attribute:

media-level

This attribute is not dependent on charset.

Purpose:

When SRTP is used, the attribute SRTPROCTxRate defines the ROC transmission rate, R.

Specification of attribute values:

The attribute value MUST be a decimal integer R between 1 and 65535 inclusive, as specified in [4] (Lehtovirta, V., Naslund, M., and K. Norrman, “Integrity Transform Carrying Roll-Over Counter for the Secure Real-time Transport Protocol (SRTP),” January 2007.). If the ROC transmission rate is not included in the negotiation, the default value of 1 SHALL be used. For details, see OMA-TS-BCAST_SvcCntProtection, Section 10.4.

6.  Acknowledgments

Many thanks to Hosame Abu-Amara, Francois Ambrosini, David Castleford, Miguel Garcia, Alfred Hoenes, Charles Lo, and Uwe Rauschenbach for their help and support.

7.  References

7.1. Normative References

7.2. Informative References

Authors' Addresses

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