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RTP Payload Crypto Profile. Michael Thomas [email protected] Packetcable Crypto Profile. Packetcable is the telephony over cable effort of NA cable operators Set of specs for signaling, provisioning, security, etc http://www.packetcable.com in interim section

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Packetcable crypto profile
Packetcable Crypto Profile

  • Packetcable is the telephony over cable effort of NA cable operators

    • Set of specs for signaling, provisioning, security, etc

    • http://www.packetcable.com in interim section

  • Security specification for media had two main goals:

    • privacy and integrity for media

    • large PSTN gateway friendly algorithms

  • Two current choices: RC-4 and MMH


Packetcable rtp packet
Packetcable RTP Packet

Covered by MMH MAC

2 or 4

byte

MAC

RTP payload

RTP header

MAC

Covered by RC-4 encryption


Mmh mac
MMH MAC

  • 2 or 4 byte MAC appended to end of payload

    • 16 byte MAC would be strong, but expensive

    • Actual barge-in threat of occasional random guessing attack acceptable

  • Applied over entire RTP packet, not just headers

    • eliminates man in the middle attack on payload

  • Signaled in SDP via ciphersuite exchange

    • Optimal use of bytes on wire (no need for pad byte)

    • Feedback that a new profile may be better

  • DSP friendly


Rc 4 payload encryption
RC-4 Payload Encryption

  • RC-4 is a cheap, strong stream cipher

  • RTP is close to a stream, except it’s unreliable

    • requires RTP headers in the clear

    • timestamps for replay protection

    • with timestamps and maximized packetization size we can always reconstruct the stream state

    • pretty optimal for fixed voice, needs more work for variable rate coders

  • Very fast, CPU-wise

    • ~10MB/sec on a P150


Conclusion
Conclusion

  • Together, RC4/MMH are very fast, and cheap

    • ~ 1kb code, 300bytes/DS0, ~.5 MIPS/DS0

    • Very DSP friendly, other transforms break budgets on one or more of the parameters

  • Could still use work for rationalizing SDP and variable rate coders

  • Nothing fundamental about the spec which cannot add larger MAC’s (SHA-1…) or different encryption (3-DES, AES, SEAL…)

  • Hopefully submit this as a draft for Pittsburgh

    • same IP tangle as DCS group in SIP


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