Revocable Encryption, Programs, and More: The Case of Multi-Copy Security
Prabhanjan Ananth, Saachi Mutreja, Alexander Poremba
TL;DR
The paper investigates provable revocation in quantum cryptography under multi-copy security, addressing the challenge that learning from multiple identical quantum copies can undermine unclonable primitives. It introduces subset states, leverages quantum pseudorandomness via QPRPs, and proves a key k→k+1 unforgeability lemma that underpins multi-copy revocable encryption, programs, and point functions in oracle models. The constructions demonstrate multi-copy revocable security in both classical and quantum oracle models and extend to sponge hashing applications, revealing broader applicability of unclonable cryptography with multi-copy security. The work suggests that multi-copy security is achievable within unclonable cryptography, potentially guiding future plain-model implementations and enabling more flexible revocation and leasing scenarios in quantum-secure environments.
Abstract
Fundamental principles of quantum mechanics have inspired many new research directions, particularly in quantum cryptography. One such principle is quantum no-cloning which has led to the emerging field of revocable cryptography. Roughly speaking, in a revocable cryptographic primitive, a cryptographic object (such as a ciphertext or program) is represented as a quantum state in such a way that surrendering it effectively translates into losing the capability to use this cryptographic object. All of the revocable cryptographic systems studied so far have a major drawback: the recipient only receives one copy of the quantum state. Worse yet, the schemes become completely insecure if the recipient receives many identical copies of the same quantum state -- a property that is clearly much more desirable in practice. While multi-copy security has been extensively studied for a number of other quantum cryptographic primitives, it has so far received only little treatment in context of unclonable primitives. Our work, for the first time, shows the feasibility of revocable primitives, such as revocable encryption and revocable programs, which satisfy multi-copy security in oracle models. This suggest that the stronger notion of multi-copy security is within reach in unclonable cryptography more generally, and therefore could lead to a new research direction in the field.