Revocable Encryption, Programs, and More: The Case of Multi-Copy Security

TL;DR

This paper demonstrates the feasibility of revocable cryptographic primitives like encryption and programs that are secure even when multiple copies are available, advancing the field of unclonable quantum cryptography.

Contribution

It introduces the first constructions of revocable primitives with multi-copy security in oracle models, addressing a key limitation of previous schemes.

Findings

Revocable primitives can be secure with multiple copies in oracle models.

Multi-copy security is achievable for unclonable cryptography.

This work opens new research directions in quantum cryptography.

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.