Huiqin Xie

Authenticated encryption with associated data (AEAD) provides confidentiality and integrity but need not commit a ciphertext to its key. We study this additional property for ACORN-128 v3 and Deoxys-I/II. Our baseline constructions use two distinct known keys and a common nonce while allowing different associated data (AD), and produce identical complete ciphertext–tag pairs. They directly witness failures of the commitment (CMT) notions for the key (CMT-1), decryption context (CMT-3), and complete encryption input (CMT-4), as well as the full-robustness notion for AEAD (AEAD-FROB) used here. For ACORN, we prove full rank of a 293-dimensional binary control matrix, guaranteeing state collisions for arbitrary initialized states; a byte-oriented implementation uses 37-byte controllable AD suffixes and can preserve a common AD prefix. For Deoxys, we instantiate the established AD-preimage technique, requiring two forward and one inverse tweakable-block-cipher calls for the empty-message Deoxys-I construction, and one forward and two inverse calls for Deoxys-II. We also derive nonempty-message constructions and verify two-key instances with both nonce and AD common by solving a binary selection system. Fixed-version reference implementations verify all reported collisions and both decryptions. These results concern commitment under the stated input control and do not establish attacks on conventional unknown-key AEAD security or on specific deployed protocols.

The combination of quantum algorithms is one promising approach to attacking symmetric cryptography. In this paper, we study in detail the Grover-meets-Simon and Alg-PolyQ2 algorithms under deferred measurement, which combine the ideas of Grover’s and Simon’s algorithms and are applicable to attacking the FX construction. By converting intermediate measurements into unitary operations deferred to the end of the quantum circuit, both quantum algorithms involve a quantum rank-solving problem. To address it, we first provide a formal analysis of the generalized quantum Gauss–Jordan elimination and characterize the resulting quantum state after the corresponding unitary operations, which serves as a subroutine in these two algorithms. Subsequently, we derive the tight bounds of the attack success probability of these two algorithms based on the initial amplitude, offering a novel perspective that confirms their effectiveness. Furthermore, our research perspective provides an idea for analyzing the attack success probability for some quantum algorithms integrating Grover’s algorithm without considering quantum input length, and contributes to a deeper understanding of these attacks’ underlying mechanisms under the deferred measurement principle.

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 2^61.5 for recovering the correct key bits and requires 531 quantum bits.

Accountable anonymous credentials protect user privacy while holding the accountability of ill-intentioned individuals, which is a critical feature for applications such as online payments and other financial services. Existing accountable anonymous credentials rely on a public committee of trustworthy members who are assumed not to collude and are well protected to perform privacy revocation. However, this assumption is unsound in blockchain-based cryptocurrency systems because the selected committees may involve nodes with significant stakes, and public nodes serving as committee members are vulnerable against targeted attacks from high-computing power adversaries. In this paper, we propose an improved accountable anonymous credential called AccCred, allowing users and issuers to randomly select a hidden committee within a set of authenticated candidates for privacy revocation. No one except the members with corresponding private keys knows their identity, preventing proactive attacks. As a core component, we introduce the primitive of dynamic triple-hiding committees (DTHC), which achieves authentication, dynamic join/delete, random selection, and strong anonymity of committee members. As a building block of DTHC, we design a shuffle protocol to provide efficient shuffle proof of randomized public keys. We formally prove our scheme and compare its performance with previous work for demonstration of practicality.

In order to design quantum-safe block ciphers, it is crucial to investigate the application of quantum algorithms to cryptographic analysis tools. In this study, we use the Bernstein–Vazirani algorithm to enhance truncated differential cryptanalysis and boomerang cryptanalysis. We first propose a quantum algorithm for finding truncated differentials, then rigorously prove that the output truncated differentials must have high differential probability for the vast majority of keys in the key space. Subsequently, based on this algorithm, we design a quantum algorithm for finding boomerang distinguishers. The quantum circuits of the two proposed quantum algorithms contain only polynomial quantum gates and qubits. Compared with classical tools for searching truncated differentials or boomerang distinguishers, the proposed algorithms can maintain the polynomial complexity while fully considering the impact of S-boxes and key scheduling.

Due to the superiority of quantum computing, traditional cryptography is facing a severe threat. This makes the security evaluation of cryptographic systems in quantum attack models both significant and urgent. For symmetric ciphers, the security analysis heavily relies on cryptanalysis tools. Thus, exploring the use of quantum algorithms in traditional cryptanalysis tools has garnered considerable attention. In this study, we utilize quantum algorithms to improve impossible differential attacks and design two quantum automated tools to search for impossible differentials. The proposed quantum algorithms exploit the idea of miss-in-the-middle and the properties of truncated differentials. We rigorously prove their validity and calculate the quantum resources required for their implementation. Compared to the existing classical automated cryptanalysis, the proposed quantum tools have the advantage of accurately characterizing S-boxes while only requiring polynomial complexity, and can take into consideration the impact of the key schedules in a single-key model.

Facing the worldwide steady progress in building quantum computers, it is crucial for cryptographic community to design quantum-safe cryptographic primitives. To achieve this, we need to investigate the capability of cryptographic analysis tools when used by the adversaries with quantum computers. In this article, we concentrate on truncated differential and boomerang cryptanalysis. We first present a quantum algorithm which is designed for finding truncated differentials of symmetric ciphers. We prove that, with a overwhelming probability, the truncated differentials output by our algorithm must have high differential probability for the vast majority of keys in key space. Afterwards, based on this algorithm, we design a quantum algorithm which can be used to find boomerang distinguishers. The quantum circuits of both quantum algorithms contain only polynomial quantum gates. Compared to classical tools for searching truncated differentials or boomerang distinguishers, our algorithms fully utilize the strengths of quantum computing, and can maintain the polynomial complexity while fully considering the impact of S-boxes and key scheduling.

Due to the superiority of quantum computing, traditional cryptography is facing severe threat. This makes the security evaluation of cryptographic systems in quantum attack models significant and urgent. For symmetric ciphers, the security analysis heavily relies on cyptanalytic tools. Thus exploring the use of quantum algorithms to traditional cyptanalytic tools has drawn a lot of attention. In this study, we utilize quantum algorithms to improve impossible differential attack, and design two quantum automatic tools for searching impossible differentials. The proposed quantum algorithms exploit the idea of miss-in-the-middle and the properties of truncated differentials. We rigorously prove their validity and calculate the quantum resources required to implement them. Compared to existing classical automatic cryptanalysis, the quantum tools proposed have the advantage of accurately characterizing S-boxes while only requiring polynomial complexity, and can take into consideration the impact of the key schedules in single-key model.