Deniable Public-Key Authenticated Quantum Key Exchange

In this work, we explore the notion of deniability in public-key authenticated quantum key exchange ( \(\textsf{QKE}\) ), which allows two parties to establish a shared secret key without leaving any evidence that would bind a session to either party. The deniability property is expressed in terms of being able to simulate the transcripts of a protocol. The ability to deny a message or an action has applications ranging from secure messaging to secure e-voting and whistle-blowing. While quite well-established in classical cryptography, it remains largely unexplored in the quantum setting. Here, we first present a natural extension of classical definitions in the simulation paradigm to the setting of quantum computation and formalize the requirements for a deniable \(\textsf{QKE}\) scheme. We then prove that the BB84 variant of \(\textsf{QKE}\) , when authenticated using a strong designated verifier signature scheme, satisfies deniability and, finally, propose a concrete instantiation.