Quantum ciphertext authentication and key recycling with the trap code
This work addresses security challenges in interactive or delegated quantum computation by providing a strong authentication method that allows key recycling, which is incremental as it builds on existing purity testing concepts.
The paper tackles the problem of ensuring ciphertext integrity and enabling key recycling in quantum authentication schemes by leveraging quantum error-correcting codes with purity testing properties, resulting in an explicit trap-based code that supports natural computation on ciphertexts.
We investigate quantum authentication schemes constructed from quantum error-correcting codes. We show that if the code has a property called purity testing, then the resulting authentication scheme guarantees the integrity of ciphertexts, not just plaintexts. On top of that, if the code is strong purity testing, the authentication scheme also allows the encryption key to be recycled, partially even if the authentication rejects. Such a strong notion of authentication is useful in a setting where multiple ciphertexts can be present simultaneously, such as in interactive or delegated quantum computation. With these settings in mind, we give an explicit code (based on the trap code) that is strong purity testing but, contrary to other known strong-purity-testing codes, allows for natural computation on ciphertexts.