1、 International Telecommunication Union ITU-T H.248.77TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (09/2010) SERIES H: AUDIOVISUAL AND MULTIMEDIA SYSTEMSInfrastructure of audiovisual services Communication procedures Gateway control protocol: Secure real-time transport protocol (SRTP) package and
2、procedures Recommendation ITU-T H.248.77 ITU-T H-SERIES RECOMMENDATIONS AUDIOVISUAL AND MULTIMEDIA SYSTEMS CHARACTERISTICS OF VISUAL TELEPHONE SYSTEMS H.100H.199 INFRASTRUCTURE OF AUDIOVISUAL SERVICES General H.200H.219 Transmission multiplexing and synchronization H.220H.229 Systems aspects H.230H.
3、239 Communication procedures H.240H.259Coding of moving video H.260H.279 Related systems aspects H.280H.299 Systems and terminal equipment for audiovisual services H.300H.349 Directory services architecture for audiovisual and multimedia services H.350H.359 Quality of service architecture for audiov
4、isual and multimedia services H.360H.369 Supplementary services for multimedia H.450H.499 MOBILITY AND COLLABORATION PROCEDURES Overview of Mobility and Collaboration, definitions, protocols and procedures H.500H.509 Mobility for H-Series multimedia systems and services H.510H.519 Mobile multimedia
5、collaboration applications and services H.520H.529 Security for mobile multimedia systems and services H.530H.539 Security for mobile multimedia collaboration applications and services H.540H.549 Mobility interworking procedures H.550H.559 Mobile multimedia collaboration inter-working procedures H.5
6、60H.569 BROADBAND, TRIPLE-PLAY AND ADVANCED MULTIMEDIA SERVICES Broadband multimedia services over VDSL H.610H.619 Advanced multimedia services and applications H.620H.629 IPTV MULTIMEDIA SERVICES AND APPLICATIONS FOR IPTV General aspects H.700H.719 IPTV terminal devices H.720H.729 IPTV middleware H
7、.730H.739 IPTV application event handling H.740H.749 IPTV metadata H.750H.759 IPTV multimedia application frameworks H.760H.769 IPTV service discovery up to consumption H.770H.779 For further details, please refer to the list of ITU-T Recommendations. Rec. ITU-T H.248.77 (09/2010) i Recommendation I
8、TU-T H.248.77 Gateway control protocol: Secure real-time transport protocol (SRTP) package and procedures Summary Recommendation ITU-T H.248.77 defines a new ITU-T H.248 package, the secure RTP package. In addition, this Recommendation covers a set of procedures related to SRTP key management. The c
9、ombination of package and procedures allows a MGC to control the use of secure RTP (SRTP) by a MG. History Edition Recommendation Approval Study Group 1.0 ITU-T H.248.77 2010-09-13 16 ii Rec. ITU-T H.248.77 (09/2010) FOREWORD The International Telecommunication Union (ITU) is the United Nations spec
10、ialized agency in the field of telecommunications, information and communication technologies (ICTs). The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them
11、with a view to standardizing telecommunications on a worldwide basis. The World Telecommunication Standardization Assembly (WTSA), which meets every four years, establishes the topics for study by the ITU-T study groups which, in turn, produce Recommendations on these topics. The approval of ITU-T R
12、ecommendations is covered by the procedure laid down in WTSA Resolution 1. In some areas of information technology which fall within ITU-Ts purview, the necessary standards are prepared on a collaborative basis with ISO and IEC. NOTE In this Recommendation, the expression “Administration“ is used fo
13、r conciseness to indicate both a telecommunication administration and a recognized operating agency. Compliance with this Recommendation is voluntary. However, the Recommendation may contain certain mandatory provisions (to ensure, e.g., interoperability or applicability) and compliance with the Rec
14、ommendation is achieved when all of these mandatory provisions are met. The words “shall“ or some other obligatory language such as “must“ and the negative equivalents are used to express requirements. The use of such words does not suggest that compliance with the Recommendation is required of any
15、party. INTELLECTUAL PROPERTY RIGHTS ITU draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. ITU takes no position concerning the evidence, validity or applicability of claimed Intellectual Propert
16、y Rights, whether asserted by ITU members or others outside of the Recommendation development process. As of the date of approval of this Recommendation, ITU had not received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However, imple
17、menters are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database at http:/www.itu.int/ITU-T/ipr/. ITU 2011 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior writte
18、n permission of ITU. Rec. ITU-T H.248.77 (09/2010) iii CONTENTS Page 1 Scope 1 1.1 Connection model . 1 2 References. 2 3 Definitions 2 3.1 Terms defined elsewhere 2 3.2 Terms defined in this Recommendation . 3 4 Abbreviations and acronyms 3 5 Conventions 3 6 Secure RTP package . 4 6.1 Properties 4
19、6.2 Events . 5 6.3 Signals 7 6.4 Statistics 7 6.5 Error codes 8 6.6 Procedures 8 7 Key management using SDP security descriptions 10 7.1 Overspecification of SRTP parameters and multiple keys . 11 7.2 Wildcarding of SRTP parameters . 11 7.3 Interoperability with offer/answer-based implementations 12
20、 7.4 SDES and SRTP cryptographic contexts . 12 7.5 Mapping of master keys for sent packets and received packets statistics 13 8 Security considerations . 13 Appendix I Example call flows . 14 I.1 Initial session setup using SDP security descriptions . 14 I.2 MG1s key is about to expire 17 I.3 Auditi
21、ng SRTP capabilities 18 I.4 Auditing of SRTP Statistics 18 Appendix II Sample use-cases of SRTP bearer encryption 20 II.1 Use-case #1: ITU-T H.248 MG for peering IP and circuit-switched networks . 20 II.2 Use case #2: ITU-T H.248 MG for peering IP networks . 20 II.3 Use case #3: Transparent SRTP for
22、warding 21 Bibliography. 23 Rec. ITU-T H.248.77 (09/2010) 1 Recommendation ITU-T H.248.77 Gateway control protocol: Secure real-time transport protocol (SRTP) package and procedures 1 Scope The secure real-time transport protocol (SRTP) is an RTP profile that provides confidentiality, message authen
23、tication and replay protection to RTP and RTCP sessions. The secure RTP package allows a MGC to control the use of SRTP by a MG. This package is defined in detail in clause 6. By itself, the secure RTP package is incomplete, as it does not provide procedures for key management. Instead, it is design
24、ed to rely on existing key-management schemes. Clause 7 provides procedures for the use of one such key-management scheme: SDP security descriptions. Several reasons exist why this Recommendation is required, in addition to the existing (usually SDP-based) SRTP key-management schemes. The most signi
25、ficant of which are listed below: Most existing SDP key-management schemes rely on the SDP offer/answer model (see b-IETF RFC 3264). However, the offer/answer model is not used in ITU-T H.248 as it does not fit the nature of the connection between an ITU-T H.248 MGC and a MG. Existing SDP key-manage
26、ment schemes do not contain procedures relating to parameter overspecification and wildcarding, which are unique to ITU-T H.248. The limited lifetime of SRTP master keys calls for mechanisms for handling master key expiry. The existing mechanisms cannot be used in ITU-T H.248. The SRTP package allow
27、s explicit control over the key-management scheme employed, allowing easy interoperability with, and migration to future schemes. The SRTP package allows an MGC to audit the SRTP capabilities of an MG through the use of the packages descriptor and the properties of the new package. The SRTP package
28、allows an MGC to collect statistics regarding the number of security violations encountered by the MG, and the volume of SRTP traffic it processed. The scope of this Recommendation is limited to use-cases in which a MG applies SRTP procedures, as described in clause 3.3 of IETF RFC 3711, to the SRTP
29、 packets it sends and receives. Use-cases in which the MG handles SRTP packets without using those procedures (e.g., transparent forwarding, storage in encrypted form, etc.) are intentionally left out of this Recommendation. 1.1 Connection model All protocol elements and procedures described in this
30、 Recommendation are limited to the extent of a single ITU-T H.248 termination. In addition, no assumptions are made regarding either the lower layer protocols beneath the SRTP level or the upper layer protocols/codecs being carried by the SRTP. This allows the use of the Recommendations procedures i
31、n various connection models and use-cases (e.g., a SRTP enabled announcement server, a SRTP to RTP translator, etc.). Figure 1 details the generic connection-model where a SRTP-enabled termination is connected to a single other termination (either SRTP-enabled or not). The generalization to any numb
32、er of terminations is trivial. 2 Rec. ITU-T H.248.77 (09/2010) H.248.77(10)_F01*ITU-T H.248 contextSRTP-enabledterminationOtherterminationRTP/RTCPLower-layerprotocolsSRTP sessionAny type of bearer/sessionLower-layer bearerUpper-layercodecsSRTP/SRTCPFigure 1 Two-termination context with a SRTP termin
33、ation 2 References The following ITU-T Recommendations and other references contain provisions which, through reference in this text, constitute provisions of this Recommendation. At the time of publication, the editions indicated were valid. All Recommendations and other references are subject to r
34、evision; users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent edition of the Recommendations and other references listed below. A list of the currently valid ITU-T Recommendations is regularly published. The reference to a document within t
35、his Recommendation does not give it, as a stand-alone document, the status of a Recommendation. ITU-T H.248.1 Recommendation ITU-T H.248.1 (2005), Gateway control protocol: Version 3, including its Amendment 1 (2008) and Amendment 2 (2009). ITU-T H.248.8 Recommendation ITU-T H.248.8 (2007), Gateway
36、control protocol: Error code and service change reason description. ITU-T H.248.47 Recommendation ITU-T H.248.47 (2008), Gateway control protocol: Statistic conditional reporting package. ITU-T H.248.49 Recommendation ITU-T H.248.49 (2007), Gateway control protocol: Session description protocol RFC
37、and capabilities packages. IETF RFC 3550 IETF RFC 3550 (2003), RTP: A Transport Protocol for Real-Time Applications. IETF RFC 3711 IETF RFC 3711 (2004), The Secure Real-time Transport Protocol (SRTP). IETF RFC 4568 IETF RFC 4568 (2006), Session Description Protocol (SDP) Security Descriptions for Me
38、dia Streams. 3 Definitions 3.1 Terms defined elsewhere This Recommendation uses the following terms defined elsewhere: 3.1.1 RTP session IETF RFC 3550: An association among a set of participants communicating with RTP. The distinguishing feature of an RTP session is that each maintains a full, separ
39、ate space of SSRC identifiers. 3.1.2 SRTP cryptographic context IETF RFC 3711: The set of cryptographic state information that an SRTP sender or receiver must maintain per SRTP session participant. NOTE 1 This term is often abbreviated as “crypto context“. Rec. ITU-T H.248.77 (09/2010) 3 3.2 Terms d
40、efined in this Recommendation This Recommendation defines the following terms: 3.2.1 decrypting master key: A SRTP master key used to decrypt and authenticate SRTP packets received by the MG. 3.2.2 encrypting master key: A SRTP master key used to encrypt and authenticate SRTP packets sent by the MG.
41、 4 Abbreviations and acronyms This Recommendation uses the following abbreviations and acronyms: AES Advanced Encryption Standard HMAC Keyed-Hash Message Authentication Code IP Internet Protocol IPSec IP Security ISDN Integrated Services Digital Network L1 Layer 1 (of the Open Systems Interconnectio
42、n model the physical layer) L2 Layer 2 (of the Open Systems Interconnection model the data link layer) MG Media Gateway MGC Media Gateway Controller MKI Master Key Identifier NAPT Network Address and Port Translation NAT Network Address Translation PSTN Public Switched Telephone Network ROC Rollover
43、 Counter RTCP RTP Control Protocol RTP Real-time Transport Protocol SDP Session Description Protocol SHA1 Secure Hash Algorithm 1 SRTCP Secure RTCP SRTP Secure RTP SSRC Synchronization Source TDM Time Division Multiplexing UDP User Datagram Protocol 5 Conventions The names of ITU-T H.248 descriptors
44、 are always capitalized, for example, Streams and Local Descriptor. The names of ITU-T H.248 properties, events, signals and parameters appear in the text in italics, for example ReserveValue. 4 Rec. ITU-T H.248.77 (09/2010) All error codes appearing in this Recommendation are described in ITU-T H.2
45、48.8 and ITU-T H.248.49. 6 Secure RTP package Package Name: Secure RTP Package ID: srtp (0x0107) Description: This package defines elements that allow the MGC to control an MGs use of the SRTP profile. Version: 1 Extends: None 6.1 Properties 6.1.1 Supported Encryption Transforms Property Name: Suppo
46、rted Encryption Transforms Property ID: set (0x0001) Description: This property declares the set of encryption transforms that can be used by SRTP sessions. Type: Sub-list of Enumeration Possible values: Each item in the list can be one of: “NULL“ (0x0000): The NULL Cipher “AES_CM_128“ (0x0001): AES
47、 in counter mode with a 128-bit key “AES_CM_192“ (0x0002): AES in counter mode with a 192-bit key “AES_CM_256“ (0x0003): AES in counter mode with a 256-bit key “AES_F8_128“ (0x0004): AES in f8 mode with a 128-bit key “AES_F8_192“ (0x0005): AES in f8 mode with a 192-bit key “AES_F8_256“ (0x0006): AES
48、 in f8 mode with a 256-bit key Default: Provisioned Defined in: TerminationState Characteristics: ReadOnly 6.1.2 Supported Authentication Transforms Property Name: Supported Authentication Transforms Property ID: sat (0x0002) Description: This property declares the set of authentication transforms t
49、hat can be used by SRTP sessions. Type: Sub-list of Enumeration Possible values: Each item in the list can be one of: “NULL“ (0x0000): The NULL authentication algorithm “HMAC_SHA1_80“ (0x0001): HMAC-SHA1 with an 80-bit tag “HMAC_SHA1_32“ (0x0002): HMAC-SHA1 with a 32-bit tag Rec. ITU-T H.248.77 (09/2010) 5 Default: Provisioned Defined in: TerminationState Characteristics: ReadOnly 6.1.3 Key Management Scheme Property Name: Key Management Scheme Property ID: km (0x0003) Description: This prope
