Post-quantum Asynchronous Deniable Key Exchange and the Signal Handshake
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Author / Producer
Date
2022
Publication Type
Conference Paper
ETH Bibliography
yes
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Abstract
The key exchange protocol that establishes initial shared secrets in the handshake of the Signal end-to-end encrypted messaging protocol has several important characteristics: (1) it runs asynchronously (without both parties needing to be simultaneously online), (2) it provides implicit mutual authentication while retaining deniability (transcripts cannot be used to prove either party participated in the protocol), and (3) it retains security even if some keys are compromised (forward secrecy and beyond). All of these properties emerge from clever use of the highly flexible Diffie-Hellman protocol.
While quantum-resistant key encapsulation mechanisms (KEMs) can replace Diffie-Hellman key exchange in some settings, there is no replacement for the Signal handshake solely from KEMs that achieves all three aforementioned properties, in part due to the inherent asymmetry of KEM operations. In this paper, we show how to construct asynchronous deniable key exchange by combining KEMs and designated verifier signature (DVS) schemes, matching the characteristics of Signal. There are several candidates for post-quantum DVS schemes, either direct constructions or via ring signatures. This yields a template for an efficient post-quantum realization of the Signal handshake with the same asynchronicity and security properties as the original Signal protocol.
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Publication status
published
External links
Book title
Public-Key Cryptography – PKC 2022
Journal / series
Volume
13178
Pages / Article No.
3 - 34
Publisher
Springer
Event
25th International Conference on Practice and Theory of Public-Key Cryptography (PKC 2022)
Edition / version
1-2
Methods
Software
Geographic location
Date collected
Date created
Subject
authenticated key exchange; deniability; asynchronous; Signal protocol; post-quantum; designated verifier signatures
Organisational unit
09653 - Paterson, Kenneth / Paterson, Kenneth