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LSEP-AC: A SEP-based Anonymous Credential from Lattice

Xian Guo, Xianzhen Chen, Wenjuan Jia, Yudan Cheng, Junli Fang, Feng Tao

Published Feb 20, 2026• 0 citations
Publisher

Abstract

The Anonymous credential is a fundamental cryptographic primitive for privacy-preserving authentication. Anonymos credentials based on signatures with efficient protocols (SEP) have attracted considerable attention due to their efficiency and compatibility with practical systems. However, most existing SEP-based anonymous credentials rely on classical hardness assumptions and are therefore not expected to withstand quantum adversaries, while post-quantum SEP instantiations remain limited in both number and efficiency. To address these limitations, a novel SEP-based anonymous credential (LSEP-AC) is proposed based on lattice-based cryptographic primitives such as the Plover signature, the LNP framework, and the Ajtai commitment in this paper. In the random oracle model, we formally prove that our LSEP-AC satisfies security properties, including correctness, anonymity, and unforgeability. The theoretical analysis and experimental evaluation both show that the anonymous credential size of the LSEP-AC is about 89.75 KB for 128 bit-security. The total verification key size of the user and issuer is around 2.52 KB, and the total secret key size of the user and issuer is around 7.74 KB, which exhibits significant advantages over related schemes.

DOI
10.36227/techrxiv.177162421.15872337/v1

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The Anonymous credential is a fundamental cryptographic primitive for privacy-preserving authentication. Anonymos credentials based on signatures with efficient protocols (SEP) have attracted considerable attention due to their efficiency and compatibility with practical systems. However, most existing SEP-based anonymous credentials rely on classical hardness assumptions and are therefore not expected to withstand quantum adversaries, while post-quantum SEP instantiations remain limited in both number and efficiency. To address these limitations, a novel SEP-based anonymous credential (LSEP-AC) is proposed based on lattice-based cryptographic primitives such as the Plover signature, the LNP framework, and the Ajtai commitment in this paper. In the random oracle model, we formally prove that our LSEP-AC satisfies security properties, including correctness, anonymity, and unforgeability. The theoretical analysis and experimental evaluation both show that the anonymous credential size of the LSEP-AC is about 89.75 KB for 128 bit-security. The total verification key size of the user and issuer is around 2.52 KB, and the total secret key size of the user and issuer is around 7.74 KB, which exhibits significant advantages over related schemes.
Anonymous credential schemes are a key application in modern cryptography. Recent research has advanced these schemes by incorporating issuer-hiding capabilities, which prevent the disclosure of the credential issuer’s identity. While several issuer-hiding anonymous credential schemes exist, none offer resilience against quantum computing adversaries. To address this gap, we propose a post-quantum issuer-hiding anonymous credential scheme, building on the recent work known as ring referral (S&P ’25), which allows anonymous signatures from third-party signers. Ring referral is an integration of ring signature and anonymous credential schemes, enabling issuer-hiding anonymous credentials. In this paper, we present an efficient lattice-based ring referral scheme, which supports quantum-resistant security. Our scheme extends a recent lattice-based credential scheme (CCS ’24) via LNP proof system (CRYPTO ’22).
Anonymous credential (AC) systems are privacy-preserving authentication mech-anisms that allow users to prove that they have valid credentials anonymously. These systems provide a powerful tool for several practical applications, such as anonymous pay-ment systems in e-commerce, preserving robust privacy protection for users. Most existing AC systems are constructed using traditional number-theoretic approaches, making them insecure under quantum attacks. With four decades of research in anonymous credential systems, there is a need for a comprehensive review that identifies the design structures of AC systems, organizes the research trends, and highlights unaddressed gaps for the future development of AC, especially bringing AC to post-quantum cryptography. This work is a complete study describing AC systems, as well as their architecture, components, security, and performance. Additionally, real-world implementations of various applications are identified, analyzed, and compared according to the design structure. Lastly, the challenges hindering the shift toward the quantumly secure lattice-based AC designs are discussed.
Among post-quantum alternatives, latticebased cryptography is the most promising one, due to its simple operations, reduction from aver-age-case to worstcase hardness, and supporting of rich functionalities. Ring signature enables a user to sign anonymously on behalf of an adaptively chosen group, and has multiple applications in anonymous e-voting, anonymous authentication, whistle blowing etc. However, most lattice-based ring signature schemes were constructed in the random oracle model from lattice basis delegation and they suffer large verification key sizes as a common disadvantage. This work proposes an efficient ring signature scheme from lattice basis delegation without random oracle based on the extended split-SIS problem, whose security is approximately as hard as the worst-case SIVP problem. Our scheme is proved to be anonymous and existentially unforgeable under latticebased assumptions. Finally, the verification key size is significantly reduced to a small constant, instead of increasing linearly with the number of ring members.
Anonymous authentication schemes such as group signatures and anonymous credentials are important privacy-protecting tools in electronic communications. The only currently known scheme based on assumptions that resist quantum attacks is the group signature scheme by Gordon et al. (ASIACRYPT 2010). We present a generalization of group signatures called anonymous attribute tokens where users are issued attribute-containing credentials that they can use to anonymously sign messages and generate tokens revealing only a subset of their attributes. We present two lattice-based constructions of this new primitive, one with and one without opening capabilities for the group manager. The latter construction directly yields as a special case the first lattice-based group signature scheme offering full anonymity (in the random-oracle model), as opposed to the practically less relevant notion of chosen-plaintext anonymity offered by the scheme of Gordon et al. We also extend our scheme to protect users from framing attacks by the group manager, where the latter creates tokens or signatures in the name of honest users. Our constructions involve new lattice-based tools for aggregating signatures and verifiable CCA2-secure encryption.
Authentication on the Internet usually has the drawback of leaking the identity of the users, or at least allowing to trace them from a server to another. Anonymous credentials overcome this issue, by allowing users to reveal the attributes necessary for the authentication, without revealing any other information (in particular not their identity). In this article, we provide a generic framework to construct anonymous credential schemes and use it to give a concrete construction of post-quantum (lattice-based) anonymous credential protocol. Our protocol thus allows for long-term security even when one considers the emergence of quantum computers able to break widely used traditional computational assumptions, such as RSA, the discrete logarithm or Diffie-Hellman. We also give a concrete implementation of our protocol, which is only one order of magnitude slower and bandwidth consuming than previous anonymous credentials that are not post-quantum.
We propose a 2-round blind signature protocol based on the random oracle heuristic and the hardness of standard lattice problems (Ring/Module-SIS/LWE and NTRU) with a signature size of 20 KB. The protocol is round-optimal and has a transcript size that can be as small as 60 KB. This blind signature is around 4 times shorter than the most compact lattice-based scheme based on standard assumptions of del Pino and Katsumata (Crypto 2022) and around 2 times shorter than the scheme of Agrawal et al. (CCS 2022) based on their newly-proposed one-more-ISIS assumption. We also propose a "keyed-verification'' blind signature scheme in which the verifier and the signer need to share a secret key. This scheme has a smaller signature size of only 48 bytes, but further work is needed to explore the efficiency of its signature generation protocol.