RTP Payload Format for the Secure Communication Interoperability Protocol (SCIP) Codec
draft-ietf-avtcore-rtp-scip-04

Payload Working Group                                          D. Hanson
Internet-Draft                                                 M. Faller
Intended status: Standards Track                                K. Maver
Expires: 21 May 2023              General Dynamics Mission Systems, Inc.
                                                        17 November 2022

    RTP Payload Format for the Secure Communication Interoperability
                         Protocol (SCIP) Codec
                     draft-ietf-avtcore-rtp-scip-04

Abstract

   This document describes the RTP payload format of the Secure
   Communication Interoperability Protocol (SCIP).  SCIP is an
   application layer protocol that defines the establishment of reliable
   secure end-to-end communications, including capabilities exchange
   with secure session establishment parameters such as codec selection,
   encryption algorithms, security levels, and cryptographic
   initialization values.  This document defines the Session Description
   Protocol (SDP) and RTP parameters needed to support SCIP over RTP.

Status of This Memo

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   Please review these documents carefully, as they describe your rights

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   and restrictions with respect to this document.  Code Components
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Conventions . . . . . . . . . . . . . . . . . . . . . . .   3
     1.2.  Abbreviations . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Background  . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Media Format Description  . . . . . . . . . . . . . . . . . .   4
   4.  Payload Format  . . . . . . . . . . . . . . . . . . . . . . .   5
     4.1.  RTP Header Fields . . . . . . . . . . . . . . . . . . . .   5
   5.  Payload Format Parameters . . . . . . . . . . . . . . . . . .   5
     5.1.  Media Subtype "audio/scip"  . . . . . . . . . . . . . . .   6
     5.2.  Media Subtype "video/scip"  . . . . . . . . . . . . . . .   7
     5.3.  Mapping to SDP  . . . . . . . . . . . . . . . . . . . . .   8
     5.4.  SDP Offer/Answer Considerations . . . . . . . . . . . . .   9
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  10
   8.  Change Controller Address . . . . . . . . . . . . . . . . . .  10
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  10
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  12

1.  Introduction

   This document details usage of the "audio/scip" and "video/scip"
   pseudo-codecs [AUDIOSCIP], [VIDEOSCIP] as a secure session
   establishment protocol and media transport protocol over RTP.  It
   details how encrypted audio and video codec payloads are transported
   in RTP packets.  It provides a reference for network security
   policymakers, network equipment OEMs, procurement personnel, and
   government agency and commercial industry representatives.  Note that
   the IP network layer does not implement SCIP as a protocol since SCIP
   operates at the application layer in endpoints.  However, the IP
   network layer should enable SCIP traffic to transparently pass
   through the network.

   SCIP is presently implemented in United States and NATO secure voice,
   video, and data products operating on commercial, private, and
   tactical IP networks worldwide using the scip media subtype.

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1.1.  Conventions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

   Best current practices for writing an RTP payload format
   specification were followed [RFC2736] [RFC8088].

   When referring to the Secure Communication Interoperability Protocol,
   the uppercase acronym "SCIP" is used.  When referring to the media
   subtype scip, lowercase "scip" is used.

1.2.  Abbreviations

   The following abbreviations are used in this document.

   AVP:      Audio/Video Profile
   DTX:      Discontinuous Transmission
   ICWG:     Interoperability Control Working Group
   IICWG:    International Interoperability Control Working Group
   NATO:     North Atlantic Treaty Organization
   SCIP:     Secure Communication Interoperability Protocol
   SDP:      Session Description Protocol

2.  Background

   The Secure Communication Interoperability Protocol (SCIP) allows the
   negotiation of several voice, data, and video applications using
   various encryption suites.  SCIP also provides several important
   characteristics that have led to its broad acceptance in the
   international user community.  These features include end-to-end
   security at the application layer, authentication of user identity,
   the ability to apply different security levels for each secure
   session, and secure communication over any end-to-end data
   connection.

   SCIP began in the United States as the Future Narrowband Digital
   Terminal (FNBDT) Protocol.  A combined Department of Defense and
   vendor consortium formed a governing organization named the
   Interoperability Control Working Group (ICWG) to manage the protocol.
   In time, the group expanded to include NATO, NATO partners and
   European vendors under the name International Interoperability
   Control Working Group (IICWG), which was later renamed the SCIP
   Working Group.

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   First generation SCIP devices operated on circuit-switched networks.
   SCIP was then expanded to radio and IP networks.  The scip media
   subtype transports SCIP secure session establishment signaling and
   secure application traffic.  The built-in negotiation and flexibility
   provided by the SCIP standards make it a natural choice for many
   scenarios that require various secure applications and associated
   encryption suites.  SCIP has been endorsed by many NATO nations as
   the secure end-to-end solution for secure voice, video, and data
   devices.  SCIP standards are currently available to participating
   government/military communities and select OEMs of equipment that
   support SCIP.

   However, SCIP must operate over global networks (including private
   and commercial networks).  Without access to necessary information to
   support SCIP, some networks may not support the SCIP media subtypes.
   Issues may occur simply because information is not as readily
   available to OEMs, network administrators, and network architects.

   This RFC provides essential information about audio/scip and video/
   scip media subtypes that enables network equipment manufacturers to
   include "scip" as a known audio and video media subtype in their
   equipment and enables network administrators to define and implement
   a compatible security policy.

   All current IP-based SCIP devices support "scip" as a media subtype.
   Registration of scip as a media subtype provides a common reference
   for network equipment manufacturers to recognize SCIP in a payload
   declaration.

3.  Media Format Description

   The "scip" media subtype indicates support for and identifies SCIP
   traffic that is being transferred using RTP.  Transcoding, lossy
   compression, or other data modifications MUST NOT be performed on the
   SCIP RTP payload.  The audio/scip and video/scip media subtype data
   streams within the network, including the VoIP network, MUST be a
   transparent relay and be treated as "clear-channel data", similar to
   the Clearmode media subtype defined by [RFC4040].  However, Clearmode
   is defined as a gateway protocol and is limited to a sample rate of
   8000 Hz and 64 kbps bandwidth only.  Clearmode is not defined for the
   higher sample and data rates required for some SCIP traffic.

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4.  Payload Format

   The RTP Packet content of SCIP traffic is dependent upon the SCIP
   session state.  SCIP secure session establishment uses protocols
   defined in SCIP-210 [SCIP210] to negotiate an application.  SCIP
   secure traffic may consist of the encrypted output of codecs such as
   MELPe [RFC8130], G.729D [RFC3551], H.264 [RFC6184] based on the
   application negotiated during SCIP secure session establishment.
   SCIP traffic is highly variable and the bit rate specified in the SDP
   [RFC8866] is OPTIONAL since discontinuous transmission (DTX) or other
   mechanisms may be used.  The SCIP payload size will vary
   considerably, especially during SCIP secure session establishment.

   The SCIP codec produces an encrypted bitstream that is transported
   over RTP.  Unlike other codecs, SCIP does not have its own upper
   layer syntax (e.g., no Network Adaptation Layer (NAL) units), but
   rather secures the output of the codecs that it uses (e.g., G.729D,
   H.264, etc.).  SCIP achieves this by encapsulating the encrypted
   codec output that has been previously formatted according to the
   relevant RTP payload specification (e.g., RFC 6184 for H.264).

4.1.  RTP Header Fields

   The SCIP RTP header fields SHALL conform to RFC 3550.

   SCIP traffic may be continuous or discontinuous.  The Timestamp field
   MUST increment based on the sampling clock for discontinuous
   transmission as described in [RFC3550], Section 5.1.  The Timestamp
   field for continuous transmission applications is dependent on the
   sampling rate of the media as specified in the media subtype's
   specification (e.g., MELPe [RFC8130]).  Note that during a SCIP
   session, both discontinuous and continuous traffic are highly
   probable.  Therefore, a jitter buffer MAY be implemented in endpoint
   devices only but SHOULD NOT be implemented in network devices.
   Additionally, network devices SHOULD NOT repacketize SCIP packets.

   The Marker bit SHALL be set to zero for discontinuous traffic.  The
   Marker bit for continuous traffic is based on the underlying media
   subtype specification.  The underlying media is opaque within SCIP
   RTP packets.

5.  Payload Format Parameters

   The SCIP RTP payload format is identified using the scip media
   subtype, which is registered in accordance with [RFC4855] and per the
   media type registration template form [RFC6838].  A clock rate of
   8000 Hz SHALL be used for "audio/scip".  A clock rate of 90000 Hz
   SHALL be used for "video/scip".

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5.1.  Media Subtype "audio/scip"

   Media type name: audio

   Media subtype name: scip

   Required parameters: N/A

   Optional parameters: N/A

   Encoding considerations: Binary.  This media subtype is only defined
   for transfer via RTP.  There SHALL be no encoding/decoding
   (transcoding) of the audio stream as it traverses the network.

   Security considerations: See Section 6.

   Interoperability considerations: N/A

   Published specifications: [SCIP210]

   Applications which use this media: N/A

   Fragment Identifier considerations: none

   Restrictions on usage: N/A

   Additional information:

      1.  Deprecated alias names for this type: N/A

      2.  Magic number(s): N/A

      3.  File extension(s): N/A

      4.  Macintosh file type code: N/A

      5.  Object Identifiers: N/A

   Person to contact for further information:

      1.  Name: Michael Faller and Daniel Hanson

      2.  Email: michael.faller@gd-ms.com and dan.hanson@gd-ms.com

   Intended usage: Common, Government and Military

   Authors:

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      Michael Faller - michael.faller@gd-ms.com

      Daniel Hanson - dan.hanson@gd-ms.com

   Change controller:

      SCIP Working Group - ncia.cis3@ncia.nato.int

5.2.  Media Subtype "video/scip"

   Media type name: video

   Media subtype name: scip

   Required parameters: N/A

   Optional parameters: N/A

   Encoding considerations: Binary.  This media subtype is only defined
   for transfer via RTP.  There SHALL be no encoding/decoding
   (transcoding) of the video stream as it traverses the network.

   Security considerations: See Section 6.

   Interoperability considerations: N/A

   Published specifications: [SCIP210]

   Applications which use this media: N/A

   Fragment Identifier considerations: none

   Restrictions on usage: N/A

   Additional information:

      1.  Deprecated alias names for this type: N/A

      2.  Magic number(s): N/A

      3.  File extension(s): N/A

      4.  Macintosh file type code: N/A

      5.  Object Identifiers: N/A

   Person to contact for further information:

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      1.  Name: Michael Faller and Daniel Hanson

      2.  Email: michael.faller@gd-ms.com and dan.hanson@gd-ms.com

   Intended usage: Common, Government and Military

   Authors:

      Michael Faller - michael.faller@gd-ms.com

      Daniel Hanson - dan.hanson@gd-ms.com

   Change controller:

      SCIP Working Group - ncia.cis3@ncia.nato.int

5.3.  Mapping to SDP

   The mapping of the above defined payload format media subtype and its
   parameters SHALL be implemented according to Section 3 of [RFC4855].

   Since SCIP includes its own facilities for capabilities exchange, it
   is only necessary to negotiate the use of SCIP within SDP Offer/
   Answer; the specific codecs to be encapsulated within SCIP are then
   negotiated via the exchange of SCIP messages.

   The information carried in the media type specification has a
   specific mapping to fields in the Session Description Protocol (SDP)
   [RFC8866], which is commonly used to describe RTP sessions.  When SDP
   is used to specify sessions employing the SCIP codec, the mapping is
   as follows:

   *  The media type ("audio") goes in SDP "m=" as the media name for
      audio/scip, and the media type ("video") goes in SDP "m=" as the
      media name for video/scip.

   *  The media subtype ("scip") goes in SDP "a=rtpmap" as the encoding
      name.  The required parameter "rate" also goes in "a=rtpmap" as
      the clock rate.

   *  The optional parameters "ptime" and "maxptime" go in the SDP
      "a=ptime" and "a=maxptime" attributes, respectively.

   An example mapping for audio/scip is:

     m=audio 50000 RTP/AVP 96
     a=rtpmap:96 scip/8000

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   An example mapping for video/scip is:

     m=video 50002 RTP/AVP 97
     a=rtpmap:97 scip/90000

   An example mapping for both audio/scip and video/scip is:

     m=audio 50000 RTP/AVP 96
     a=rtpmap:96 scip/8000
     m=video 50002 RTP/AVP 97
     a=rtpmap:97 scip/90000

   The application negotiation between endpoints will determine whether
   the audio and video streams are transported as separate streams over
   the audio and video payload types or as a single media stream on the
   video payload type.

5.4.  SDP Offer/Answer Considerations

   In accordance with the SDP Offer/Answer model [RFC3264], the SCIP
   device SHALL list the SCIP payload type number in order of preference
   in the "m" media line.

6.  Security Considerations

   RTP packets using the payload format defined in this specification
   are subject to the security considerations discussed in the RTP
   specification [RFC3550], and in any applicable RTP profile such as
   RTP/AVP [RFC3551], RTP/AVPF [RFC4585], RTP/SAVP [RFC3711], or RTP/
   SAVPF [RFC5124].  However, as "Securing the RTP Protocol Framework:
   Why RTP Does Not Mandate a Single Media Security Solution" [RFC7202]
   discusses, it is not an RTP payload format's responsibility to
   discuss or mandate what solutions are used to meet the basic security
   goals like confidentiality, integrity, and source authenticity for
   RTP in general.  This responsibility lays on anyone using RTP in an
   application.  They can find guidance on available security mechanisms
   and important considerations in "Options for Securing RTP Sessions"
   [RFC7201].  Applications SHOULD use one or more appropriate strong
   security mechanisms.  The rest of this Security Considerations
   section discusses the security impacting properties of the payload
   format itself.

   This RTP payload format and its media decoder do not exhibit any
   significant non-uniformity in the receiver-side computational
   complexity for packet processing, and thus do not inherently pose a
   denial-of-service threat due to the receipt of pathological data.
   Nor does the RTP payload format contain any active content.

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7.  IANA Considerations

   The audio/scip and video/scip media subtypes have previously been
   registered with IANA [AUDIOSCIP] [VIDEOSCIP].  IANA should update
   [AUDIOSCIP] and [VIDEOSCIP] to reference this document upon
   publication.

8.  Change Controller Address

   SCIP Working Group, CIS3 Partnership
   NATO Communications and Information Agency
   Oude Waalsdorperweg 61, 2597AK
   The Hague, The Netherlands
   Email: ncia.cis3@ncia.nato.int

9.  References

9.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC2736]  Handley, M. and C. Perkins, "Guidelines for Writers of RTP
              Payload Format Specifications", BCP 36, RFC 2736,
              DOI 10.17487/RFC2736, December 1999,
              <https://www.rfc-editor.org/info/rfc2736>.

   [RFC3264]  Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
              with Session Description Protocol (SDP)", RFC 3264,
              DOI 10.17487/RFC3264, June 2002,
              <https://www.rfc-editor.org/info/rfc3264>.

   [RFC3550]  Schulzrinne, H., Casner, S., Frederick, R., and V.
              Jacobson, "RTP: A Transport Protocol for Real-Time
              Applications", STD 64, RFC 3550, DOI 10.17487/RFC3550,
              July 2003, <https://www.rfc-editor.org/info/rfc3550>.

   [RFC3551]  Schulzrinne, H. and S. Casner, "RTP Profile for Audio and
              Video Conferences with Minimal Control", STD 65, RFC 3551,
              DOI 10.17487/RFC3551, July 2003,
              <https://www.rfc-editor.org/info/rfc3551>.

   [RFC3711]  Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.
              Norrman, "The Secure Real-time Transport Protocol (SRTP)",
              RFC 3711, DOI 10.17487/RFC3711, March 2004,
              <https://www.rfc-editor.org/info/rfc3711>.

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   [RFC4585]  Ott, J., Wenger, S., Sato, N., Burmeister, C., and J. Rey,
              "Extended RTP Profile for Real-time Transport Control
              Protocol (RTCP)-Based Feedback (RTP/AVPF)", RFC 4585,
              DOI 10.17487/RFC4585, July 2006,
              <https://www.rfc-editor.org/info/rfc4585>.

   [RFC5124]  Ott, J. and E. Carrara, "Extended Secure RTP Profile for
              Real-time Transport Control Protocol (RTCP)-Based Feedback
              (RTP/SAVPF)", RFC 5124, DOI 10.17487/RFC5124, February
              2008, <https://www.rfc-editor.org/info/rfc5124>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8866]  Begen, A., Kyzivat, P., Perkins, C., and M. Handley, "SDP:
              Session Description Protocol", RFC 8866,
              DOI 10.17487/RFC8866, January 2021,
              <https://www.rfc-editor.org/info/rfc8866>.

9.2.  Informative References

   [AUDIOSCIP]
              Faller, M. and D. Hanson, "audio/scip: Internet Assigned
              Numbers Authority (IANA)", 28 January 2021,
              <https://www.iana.org/assignments/media-types/audio/scip>.

   [RFC4040]  Kreuter, R., "RTP Payload Format for a 64 kbit/s
              Transparent Call", RFC 4040, DOI 10.17487/RFC4040, April
              2005, <https://www.rfc-editor.org/info/rfc4040>.

   [RFC4855]  Casner, S., "Media Type Registration of RTP Payload
              Formats", RFC 4855, DOI 10.17487/RFC4855, February 2007,
              <https://www.rfc-editor.org/info/rfc4855>.

   [RFC6184]  Wang, Y.-K., Even, R., Kristensen, T., and R. Jesup, "RTP
              Payload Format for H.264 Video", RFC 6184,
              DOI 10.17487/RFC6184, May 2011,
              <https://www.rfc-editor.org/info/rfc6184>.

   [RFC6838]  Freed, N., Klensin, J., and T. Hansen, "Media Type
              Specifications and Registration Procedures", BCP 13,
              RFC 6838, DOI 10.17487/RFC6838, January 2013,
              <https://www.rfc-editor.org/info/rfc6838>.

   [RFC7201]  Westerlund, M. and C. Perkins, "Options for Securing RTP
              Sessions", RFC 7201, DOI 10.17487/RFC7201, April 2014,
              <https://www.rfc-editor.org/info/rfc7201>.

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   [RFC7202]  Perkins, C. and M. Westerlund, "Securing the RTP
              Framework: Why RTP Does Not Mandate a Single Media
              Security Solution", RFC 7202, DOI 10.17487/RFC7202, April
              2014, <https://www.rfc-editor.org/info/rfc7202>.

   [RFC8088]  Westerlund, M., "How to Write an RTP Payload Format",
              RFC 8088, DOI 10.17487/RFC8088, May 2017,
              <https://www.rfc-editor.org/info/rfc8088>.

   [RFC8130]  Demjanenko, V. and D. Satterlee, "RTP Payload Format for
              the Mixed Excitation Linear Prediction Enhanced (MELPe)
              Codec", RFC 8130, DOI 10.17487/RFC8130, March 2017,
              <https://www.rfc-editor.org/info/rfc8130>.

   [SCIP210]  SCIP Working Group, "SCIP Signaling Plan", SCIP-210,
              r3.10, October 2017.

   [VIDEOSCIP]
              Faller, M. and D. Hanson, "video/scip: Internet Assigned
              Numbers Authority (IANA)", 28 January 2021,
              <https://www.iana.org/assignments/media-types/video/scip>.

Authors' Addresses

   Daniel Hanson
   General Dynamics Mission Systems, Inc.
   150 Rustcraft Road
   Dedham, MA 02026
   United States of America
   Email: dan.hanson@gd-ms.com

   Michael Faller
   General Dynamics Mission Systems, Inc.
   150 Rustcraft Road
   Dedham, MA 02026
   United States of America
   Email: michael.faller@gd-ms.com

   Keith Maver
   General Dynamics Mission Systems, Inc.
   150 Rustcraft Road
   Dedham, MA 02026
   United States of America
   Email: keith.maver@gd-ms.com

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