The Undeniable Truth
summary
Claim: remote attestation lets an attacker turn cryptographic deniability into transferable proof. Implementation: modified Signal CLI that moves Signal’s crypto state into an Intel SGX enclave and produces an attested Signal transcript (demo shown by video after live issues). Result: published attestation + transcript convinces any verifier that messages were genuinely authenticated, defeating deniability. Mitigations: online deniable protocols (OTRv4), embedding attestation in the protocol, or adding human-verifiable keys.
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chapters (26)
- 0:00Intro
- 0:52Outline
- 1:44Hardware-security mechanisms are pervasive
- 5:45What is remote attestation?
- 6:46Attestation requirements
- 8:21Attestation Protocol
- 9:38Attestation in practice
- 12:14Desiderata for messaging protocols
- 13:52The limits of deniability?
- 15:42When is (cryptographic) deniability useful?
- 16:54A new kind of attack
- 17:43The dangers of undeniable communications
- 19:35What do deniable protocols look like?
- 20:35Deniable protocols: Off-the-Record (OTR)
- 21:52Deniable protocols: Signal Protocol
- 26:25An overview of our attack
- 27:53Key point: TEEs let us prove that a key was secret
- 29:09Modifying a Signal client
- 30:21The result: an attested transcript
- 31:27Demo
- 35:03Switch to online-deniable protocols
- 39:23Defensive remote attestation
- 41:28Put the human in the loop
- 43:09Countermeasures
- 45:08Not just messaging protocols
- 45:55Black Hat Sound Bytes
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