The Signal Protocol for the Post-Quantum Era (Q22c)

Signal is the most popular end-to-end encryption protocol in use today, providing billions of users with asynchronous messaging, forward secrecy, and deniability. Diffie-Hellman key-exchange is at the core of the protocol’s security, and therefore requires replacement with quantum-resistant alternatives to take Signal into the post-quantum age. This talk details the challenges encountered when migrating Signal to use quantum-resistant algorithms. It describes how the lack of post-quantum Diffie-Hellman ‘equivalents’ necessitates changes to the protocol, and subsequently a trade-off between security and usability properties when practically applied.