Efficient Quantum Generic Key-Recovery Attack on Feistel Ciphers

The development of post-quantum cryptography requires cryptographic primitives that remain secure against quantum adversaries. Quantum key-recovery attacks constitute a fundamental class of quantum cryptanalytic techniques, and the resistance of a cryptosystem to such attacks serves as an important indicator of its overall security. Since the Feistel structure is a core component in the design of many block ciphers, efficient quantum key-recovery attacks on Feistel ciphers provide valuable insights into evaluating and strengthening their security. In this paper, we propose an efficient generic quantum key-recovery attack on Feistel ciphers. Our attack integrates universal hash families with Simon's and Grover's algorithms to perform key-recovery. We rigorously analyze the correctness of the proposed attack and derive its time and quantum resource complexities. A comprehensive comparison with existing keyrecovery attacks shows that the proposed approach improves both quantum resource usage and dominant query complexity, and therefore yields a more efficient quantum key-recovery attack. Our work enhances the understanding of Feistel ciphers under quantum threats and informs the design of robust cryptosystems for the post-quantum era.