The Feistel structure represents a fundamental architectural component within the domain of symmetric cryptographic algorithms, with a substantial body of research conducted within the context of classical computing environments. Nevertheless, research into specific symmetric cryptographic algorithms utilizing the Feistel structure is relatively scarce in quantum computing environments. This paper, for the first time, proposes a five-round distinguisher for Camellia under the quantum chosen-ciphertext attack (qCCA) setting, with its effectiveness empirically validated. Additionally, by combining Grover’s algorithm and Simon’s algorithm, we construct a nine-round key-recovery attack model against Camellia. Through an in-depth analysis of Camellia’s key expansion algorithm, we significantly reduce the complexity of the key-recovery attack. The proposed attack achieves a time complexity of 261.5 for recovering the correct key bits and requires 531 quantum bits.
Quantum algorithms are raising concerns in the field of cryptography all over the world. A growing number of symmetric cryptography algorithms have been attacked in the quantum setting. Type-3 generalized Feistel scheme (GFS) and unbalanced Feistel scheme with expanding functions (UFS-E) are common symmetric cryptography schemes, which are often used in cryptographic analysis and design. We propose quantum distinguishing attacks on Type-3 GFS and UFS-E in the quantum chosen plaintext attack setting. The results of key recovery are better than those based on exhaustive search in the quantum setting.
In this paper, we study applications of Bernstein–Vazirani algorithm and present several new methods to attack block ciphers. Specifically, we first present a quantum algorithm for finding the linear structures of a function. Based on it, we propose new quantum distinguishers for the 3-round Feistel scheme and a new quantum algorithm to recover partial key of the Even–Mansour construction. Afterwards, by observing that the linear structures of a encryption function are actually high probability differentials of it, we apply our algorithm to differential analysis and impossible differential cryptanalysis respectively. We also propose a new kind of differential cryptanalysis, called quantum small probability differential cryptanalysis, based on the fact that the linear structures found by our algorithm are also the linear structure of each component function. To our knowledge, no similar method was proposed before. The efficiency and success probability of all attacks are analyzed rigorously. Since our algorithm treats the encryption function as a whole, it avoid the disadvantage of traditional differential cryptanalysis that it is difficult to extending the differential path.
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.
With the rapid advancement of quantum computing, the security of traditional cryptographic systems is facing significant challenges. As a fundamental component of symmetric cryptography, block ciphers have attracted increasing attention regarding their quantum security in recent years.
In this paper, we propose new quantum attacks on two Feistel-type constructions, i.e., New Structure IV and the lightweight block cipher LBlock, under the quantum chosen-plaintext attack (qCPA) model. First, we construct an 8-round quantum distinguisher for New Structure IV and perform an
r(r>12)-round quantum key-recovery attack. Compared with Li et al.'s qCPA-based result presented at INSCRYPT 2024, our attack reduces the time complexity by a factor of
2n/2, where
n denotes the subkey length. Second, we design a 9-round quantum distinguisher for LBlock and extend it to an
r(r>15)-round quantum key-recovery attack. The proposed quantum distinguisher covers one more round than Liu et al.'s automated-search distinguisher at ASIACRYPT 2025, which results in a
216 reduction in the time complexity of our
r-round quantum key-recovery attack on LBlock. Furthermore, by analyzing the structure of the round function and the key scheduling of LBlock, we reduce the subkey guess space for the 15-round attack from 76 bits to 52 bits, lowering the time complexity from
O(238) to
O(226) by a factor of
212.
It turned out that in addition to problems with classical asymmetric cryptography in the post-quantum period, there are certain doubts about the strength of symmetric cryptographic schemes.This paper demonstrates that on Type III Generalized Feistel Scheme (GFS), by selectively fixing specific parts of the plaintext at the input to the GFS, it is possible to reduce the problem of distinguishing between random text and encrypted output of the same GFS to the Simon problem through different approaches.Our method enables the cracking of the cipher up to 𝑑 rounds in polynomial time, while a more sophisticated approach based on different formulas from other paths of the cipher can crack 𝑑 + 1 rounds with the same time complexity in quantum adversary model.These distinct approaches yield varying results in terms of scheme security, indicating the potential to break more rounds in the GFS using the same methodology.