Paper 2025/2233

Quantum Authentication: Security against Authentication and Verification Queries

Abstract

Quantum authentication is a procedure that sends a quantum message to a receiver without being imperceptibly changed in the channel. How to formalize a proper authentication model is a highly non-trivial task. Existing models have various flaws: they either do not capture serious concerns or are over restricted. Most importantly, none of them have addressed the threat from the verification queries. We show that there is a quantum authentication scheme that is secure when no verification query is allowed while it is completely insecure when verification queries are additionally permitted. The threat of verification queries is not artificial. Our attack only needs to know if a forged authentication message is valid or not. It captures the concern that the adversary can watch if the receiver accepts an authentication or not, without even reading the message authenticated. We propose a quantum authentication model that captures the authentication of multiple messages under the same key as well as the verification queries. We allow the attacker to have his own state entangled with the authentication message. Finally, we propose an authentication framework abstracted from the AQA method in Garg et al. (CRYPTO'17) and prove the security in our model. Our result reduces the security of an authentication protocol to certain properties of its component primitives. We also prove that an impersonation attack implies a substitution attack. To our knowledge, this is the first time to confirm this result.