How to Copy-Protect Malleable-Puncturable Cryptographic Functionalities Under Arbitrary Challenge Distributions

TL;DR

This paper introduces a quantum copy-protection scheme for a broad class of cryptographic functionalities called malleable-puncturable schemes, achieving security against arbitrary high min-entropy challenge distributions, expanding the scope of copy-protectable primitives.

Contribution

We define malleable-puncturable schemes and develop a quantum copy-protection scheme secure against arbitrary high min-entropy challenge distributions, broadening the class of copy-protectable functionalities.

Findings

Secure against arbitrary high min-entropy challenge distributions.

Generalizes copy-protection to a wider class of schemes.

Extends beyond pseudorandom puncturing points.

Abstract

A quantum copy-protection scheme (Aaronson, CCC 2009) encodes a functionality into a quantum state such that given this state, no efficient adversary can create two (possibly entangled) quantum states that are both capable of running the functionality. There has been a recent line of works on constructing provably-secure copy-protection schemes for general classes of schemes in the plain model, and most recently the recent work of \c{C}akan and Goyal (IACR Eprint, 2025) showed how to copy-protect all cryptographically puncturable schemes with pseudorandom puncturing points. In this work, we show how to copy-protect even a larger class of schemes. We define a class of cryptographic schemes called malleable-puncturable schemes where the only requirement is that one can create a circuit that is capable of answering inputs at points that are unrelated to the challenge in the security game but does not help the adversary answer inputs related to the challenge. This is a flexible generalization of puncturable schemes, and can capture a wide range of primitives that was not known how to copy-protect prior to our work. Going further, we show that our scheme is secure against arbitrary high min-entropy challenge distributions whereas previous work has only considered schemes that are punctured at pseudorandom points.