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.

Because of the substantial progress in quantum computing technology, the safety of traditional cryptologic schemes is facing serious challenges. In this study, we explore the quantum safety of the lightweight cipher MIBS and propose quantum key-recovery attacks on the MIBS cipher by utilizing Grover’s algorithm and Bernstein–Vazirani algorithm. We first construct linear-structure functions based on the 5-round MIBS cipher according to the characteristics of the linear transformations, and then we obtain a quantum distinguisher of the 5-round MIBS cipher by applying Bernstein–Vazirani algorithm to the constructed functions. Finally, utilizing this distinguisher and Grover’s algorithm, we realize a 7-round key-recovery attack on the MIBS cipher, and then we expand the attack to more rounds of MIBS based on a similar idea. The quantum attack on the 7-round MIBS requires 156 qubits and has a time complexity of $2^{10.5}$. An 8-round attack requires 179 qubits and has a time complexity of $2^{22}$. Compared with existing quantum attacks, our attacks have better time complexity when attacking the same number of rounds.

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.

Anonymous single sign-on systems allow users to use a single credential to access multiple services protected by verifiers without revealing their personal information, which is especially important due to privacy regulations such as GDPR. In this paper, we introduce a new strong privacy-preserving single sign-on scheme, dubbed PriSign, based on our proposed attribute-based credential with traceability (ABCT), attribute-based credential with blindness (ABCB), and threshold inner-product functional encryption (TIPFE). Compared with the existing state-of-the-art solutions, PriSign presents three improvements: (1) users can obtain different types of tickets according to the attribute disclosure policies enforced by the ticket issuer to support fine-grained access control; (2) users can hide access tokens and designate a verifier for tokens according to a verifier’s policy jointly issued by multiple policymakers, meaning that non-designated verifiers cannot obtain any information about the tokens; (3) we innovatively use a threshold approach to issue policy keys online in order for verifiers to achieve proxy re-verification services in an unstable cloud environment. We implement PriSign and compare the performance with other ASSO systems in the personal laptop, and the results prove its practicability.