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Encrypted Key Transport for Secure RTP draft-mcgrew-srtp-ekt-00.txt

Encrypted Key Transport for Secure RTP draft-mcgrew-srtp-ekt-00.txt. David McGrew Flemming Andreasen Lakshminath Dondeti. Overview. In-band keying, protected by separate RTP session-level key Conveys SRTP master key and ROC Contains ‘Offer’ correlator Security Parameter Index (SPI)

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Encrypted Key Transport for Secure RTP draft-mcgrew-srtp-ekt-00.txt

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  1. Encrypted Key Transportfor Secure RTPdraft-mcgrew-srtp-ekt-00.txt David McGrew Flemming Andreasen Lakshminath Dondeti MSEC / IETF 65

  2. Overview • In-band keying, protected by separate RTP session-level key • Conveys SRTP master key and ROC • Contains ‘Offer’ correlator • Security Parameter Index (SPI) • Indicates key scope • Initial Sequence Number (ISN) • Uses SRTCP Authentication Tag for transport • Could use SRTP Auth Tag or Header Extension MSEC / IETF 65

  3. How it works SRTCP Packet SRTCP Processing EKT Data SRTP source Master key ROC Initial SEQ Decrypt Session Organizer EKT key MSEC / IETF 65

  4. Authentication Tag Format 0 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ : Base Authentication Tag : +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ : Encrypted Master Key : +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Rollover Counter | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Initial Sequence Number | Security Parameter Index | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ MSEC / IETF 65

  5. Architectural View Establishes parameters and session keys Invites members to SRTP session Signaling Transports source keys, ROCs Indicates ‘Offer’ in SPI Indicates key scope EKT Protects media Generates source keys as needed SRTP MSEC / IETF 65

  6. Late Joiners SRTP SRTCP Sender Reports MSEC / IETF 65

  7. Scalability SRTP SRTCP MSEC / IETF 65

  8. New RTP Sources Signaling Source A { Key A }EKT Key Source B { Key B }EKT Key MSEC / IETF 65

  9. Benefits • EKT decouples SRTP from signaling • Allows endpoints to start up (or rekey) SRTP sources at will • Allows participants to join sessions that are already in progress • No central coordination of ROCs, SSRCs, or SRTP’s per-source master keys required • Allows SRTP to indicate cryptosuite • Solves SIP Early Media problem without Preconditions MSEC / IETF 65

  10. Benefits (continued) • High scalability • SRTCP receiver reports ‘carry own keys’ • Can work with any SRTP keying system • Transports keys rather than setting them • No extra round trips • Benefits multiparty RTP • SIP parallel forking MSEC / IETF 65

  11. EKT Limitations • Requires SRTCP • Could be extended to use SRTP • Requires EKT secret keys established through out-of-band means • Could be extended to work with Diffie-Hellman • Provides group security after SIP parallel fork • But meets all SRTP security requirements • Adds ~ 24 bytes to each SRTCP packet • No parameter negotiation MSEC / IETF 65

  12. Future Work • Standards track? • Implement in libsrtp • mpeg4ip integration • Incorporate feedback • Extend MIKEY bindings • Define bindings to DTLS-RTP and/or SDP DH • SRTP transport method MSEC / IETF 65

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