A Variational Quantum Attack for AES-like Symmetric Cryptography

TL;DR

This paper introduces a variational quantum attack algorithm for AES-like cryptography, demonstrating potential speed advantages and highlighting the role of entanglement in quantum cryptanalysis.

Contribution

It presents a novel variational quantum attack method tailored for AES-like ciphers, with specific ansatz and cost functions, and explores entanglement's impact on attack efficiency.

Findings

VQAA can outperform Grover's algorithm in some cases.

Entanglement correlates with the attack's speedup.

Simulation results validate the effectiveness of the proposed method.

Abstract

We propose a variational quantum attack algorithm (VQAA) for classical AES-like symmetric cryptography, as exemplified the simplified-data encryption standard (S-DES). In the VQAA, the known ciphertext is encoded as the ground state of a Hamiltonian that is constructed through a regular graph, and the ground state can be found using a variational approach. We designed the ansatz and cost function for the S-DES's variational quantum attack. It is surprising that sometimes the VQAA is even faster than Grove's algorithm as demonstrated by our simulation results. The relationships of the entanglement entropy, concurrence and the cost function are investigated, which indicate that entanglement plays a crucial role in the speedup.