Multi-Copy Security in Unclonable Cryptography

2025-10-14

AI Summary

This paper addresses the hitherto unexplored problem of *multi-copy security* in unclonable cryptography. We propose the first generic multi-copy secure compilation framework, built solely on standard one-way functions, which upgrades collusion-resistant unclonable primitives to achieve multi-copy security while remaining compatible with advanced cryptographic techniques such as functional encryption. Our main contributions are: (1) formal definition and construction of *upgradable quantum coins*, enabling a smooth transition from weak verification to fully public verification; (2) the first unclonable encryption scheme achieving *multi-challenge security*; and (3) efficient realizations—under standard assumptions—of multi-copy secure quantum money and single-decryptor encryption. Our results demonstrate that high-security, practically flexible unclonable cryptographic systems can be realized without relying on strong quantum assumptions.

Technology Category

• Multiagent Systems: Multiagent Systems under Uncertainty
• Computer Vision: Multi-modal Vision
• Machine Learning: Quantum Machine Learning

Application Category

• Security and Privacy: Cryptocurrency and smart contracts
• Economics, Online Markets and Human Computation: Economic aspects of blockchain and cryptocurrencies
• Responsible Web: Measurement, analysis, and circumvention of Web censorship

Abstract

Unclonable cryptography leverages the quantum no-cloning principle to copy-protect cryptographic functionalities. While most existing works address the basic single-copy security, the stronger notion of multi-copy security remains largely unexplored. We introduce a generic compiler that upgrades collusion-resistant unclonable primitives to achieve multi-copy security, assuming only one-way functions. Using this framework, we obtain the first multi-copy secure constructions of public-key quantum money (termed quantum coins), single-decryptor encryption, unclonable encryption, and more. We also introduce an extended notion of quantum coins, called upgradable quantum coins, which allow weak (almost-public) verification under weaker assumptions and can be upgraded to full public verification under stronger assumptions by the bank simply publishing additional classical information. Along the way, we give a generic compiler that upgrades single-copy secure single-decryptor encryption to a collusion-resistant one, assuming the existence of functional encryption, and construct the first multi-challenge secure unclonable encryption scheme, which we believe are of independent interest.

Problem

• Achieving multi-copy security for unclonable cryptographic primitives
• Developing quantum coins with upgradable public verification capabilities
• Constructing collusion-resistant single-decryptor encryption from weaker assumptions

Innovation

• Generic compiler upgrades primitives for multi-copy security
• Framework enables first multi-copy secure quantum coins
• Upgradable quantum coins allow weak to full verification