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RTP Payload Crypto Profile

RTP Payload Crypto Profile. Michael Thomas mat@cisco.com. 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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RTP Payload Crypto Profile

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  1. RTP Payload Crypto Profile Michael Thomas mat@cisco.com

  2. 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

  3. Packetcable RTP Packet Covered by MMH MAC 2 or 4 byte MAC RTP payload RTP header MAC Covered by RC-4 encryption

  4. 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

  5. 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

  6. 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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