A note on quantum related-key attacks

TL;DR

This paper demonstrates that quantum adversaries can efficiently perform related-key attacks on block ciphers under certain conditions, highlighting potential quantum vulnerabilities in cryptographic schemes.

Contribution

It introduces a quantum related-key attack model showing how keys can be efficiently extracted when specific conditions are met.

Findings

Quantum related-key attacks are powerful against certain block ciphers.

Keys can be recovered efficiently using superposition queries.

The attack applies when the key is determined by few plaintext-ciphertext pairs.

Abstract

In a basic related-key attack against a block cipher, the adversary has access to encryptions under keys that differ from the target key by bit-flips. In this short note we show that for a quantum adversary such attacks are quite powerful: if the secret key is (i) uniquely determined by a small number of plaintext-ciphertext pairs, (ii) the block cipher can be evaluated efficiently, and (iii) a superposition of related keys can be queried, then the key can be extracted efficiently.