Paper 2021/571

Post-Quantum Cryptography: Computational-Hardness Assumptions and Beyond

Thomas Attema, Nicole Gervasoni, Michiel Marcus, and Gabriele Spini

Abstract

The advent of a full-scale quantum computer will severely impact most currently-used cryptographic systems. The most well-known aspect of this impact lies in the computational-hardness assumptions that underpin the security of most current public-key cryptographic systems: a quantum computer can factor integers and compute discrete logarithms in polynomial time, thereby breaking systems based on these problems. However, simply replacing these problems by other which are (believed to be) impervious even to a quantum computer does not completely solve the issue. Indeed, many security proofs of cryptographic systems are no longer valid in the presence of a quantum-capable attacker; while this does not automatically implies that the affected systems would be broken by a quantum computer, it does raises questions on the exact security guarantees that they can provide. This overview document aims to analyze all aspects of the impact of quantum computers on cryptographic, by providing an overview of current quantum-hard computational problems (and cryptographic systems based on them), and by presenting the security proofs that are affected by quantum-attackers, detailing what is the current status of research on the topic and what the expected effects on security are.