Tanuki: New Frameworks for (Concurrently Secure) Blind Signatures from Post-Quantum Groups Actions.

Lucjan Hanzlik, Yi-Fu Lai, Marzio Mula, Eugenio Paracucchi, Daniel Slamanig, Gang Tang

Published Jan 1, 2025• 0 citations

Abstract

Blind signatures are fundamental cryptographic primitives enabling privacy-preserving authentication and have seen renewed interest in the post-quantum literature. Existing efficient constructions predominantly rely on Fischlin’s generic paradigm instantiated over lattice assumptions, while blinding techniques for Σ-protocol-based blind signatures remain sparse beyond lattices. Moreover, achieving provable concurrent security under polynomially many sessions has been a longstanding open challenge for this approach in the post-quantum literature as evidenced by the recent attacks in EC’24 and PKC’24. This work broadens the landscape of post-quantum blind signatures by introducing novel techniques and proposing four frameworks based on general cryptographic group actions, without requiring commutativity. Our constructions admit instantiations under diverse post-quantum assumptions, including CSIDH (isogeny-based), LESS (code-based, NIST round-two), and more. These frameworks offer flexible trade-offs in assumptions (from interactive one-more to the standard inversion problem) and key/signature sizes, and culminate in a construction that achieves security under polynomially many concurrent sessions. This enables the first efficient blind signatures from isogenies and codes with provable concurrent security with 4.5 and 64.7 KB respectively. We also outline several directions for optimization and further instantiations for future work.

DOI: 10.60882/cispa.32779959

Related papers

Improved algorithms of post-quantum cryptographic group actions

Gilchrist, Valerie

Our modern world is dependent on online communications and transactions. To ensure privacy in these digital actions, it is extremely common to use protocols such as the Diffie-Hellman key exchange scheme. Unfortunately, these systems have been shown to be vulnerable to attacks from a quantum adversary. This means that an overhaul of the field of cryptography is needed in order to anticipate and mitigate this threat.Over the past years, the community has begun to answer this call by proposing and analyzing new techniques that are conjectured to be quantum safe. One such example is the study of cryptographic group actions. These mappings mimic some of the structure from the Diffie-Hellman protocol,but abstract it enough so that new mathematical operations can be employed that avoid quantum attacks. Currently, the main examples of group actions come from isogenies, codes, and lattices.In order for a protocol to be used in the real-world we would hope for it to be secure, fast, and requiring little storage. This means that in these early stages of research and development of cryptographic group actions, it is essential to begin to answer some of the questions surrounding security and efficiency. This thesis contributes to this effort by focusing on these aspects across different group actions that have been proposed for use in the literature.It is certainly true that each individual group action needs its own study of security. When designers are trying to achieve some advanced functionalities in a protocol, they may sometimes alter the underlying security assumptions.Each time this is done, the new assumptions need their own careful study as well. In this thesis we consider four different variants of group action security assumptions spanning the isogeny, tensor, linear code, and matrix code group actions. We analyze their security by either offering concrete attacks or giving a polynomial time reduction to a more well-studied assumption. This helps to indicate whether a problem is appropriate for use in cryptography, and what parameters to use if so.In addition to security, this thesis is also inscribed in the effort to study the efficiency of group actions by including three works studying the isogeny group action and related subroutines. They span the core isogeny problem for oriented elliptic curves, evaluating isogenies from a kernel generator, and supersingularity testing. With an effort from the community to improve overall runtimes, we can hope to get closer to reasonable speeds for real-life use.By studying the security and efficiency of cryptographic group actions, this thesis shines light on group actions as a promising framework for post-quantum cryptographic solutions.

Nov 25, 20250 citations

Practical Post-Quantum Signatures for Privacy

Sven Argo, Tim E. Güneysu, Corentin Jeudy +3 more

The transition to post-quantum cryptography has been an enormous challenge and effort for cryptographers over the last decade, with impressive results such as the future NIST standards. However, the latter has so far only considered central cryptographic mechanisms (signatures or KEM) and not more advanced ones, e.g., targeting privacy-preserving applications. Of particular interest is the family of solutions called blind signatures, group signatures and anonymous credentials, for which standards already exist, and which are deployed in billions of devices. Such a family does not have, at this stage, an efficient post-quantum counterpart although very recent works improved this state of affairs by offering two different alternatives: either one gets a system with rather large elements but a security proved under standard assumptions or one gets a more efficient system at the cost of ad-hoc interactive assumptions or weaker security models. Moreover, all these works have only considered size complexity without implementing the quite complex building blocks their systems are composed of. In other words, the practicality of such systems is still very hard to assess, which is a problem if one envisions a post-quantum transition for the corresponding systems/standards.

ACM SIGSAC Conference on Computer and Communications Security (CCS)Dec 2, 202420 citations

Lattice-Based Threshold Blind Signatures

Sebastian Faller, Guilhem Niot, Michael Reichle

Blind signatures are a central tool for privacy-preserving protocols. They allow users to obtain signatures from a signer without the signer seeing the signed message. For instance, it enables electronic cash: signatures correspond to coins which can be issued by the bank in a privacy-preserving manner via blind signing. To mitigate the risk of key compromise, threshold blind signatures allow the distribution of the signing key amongst N parties. While recent works have focused on improving the security of this primitive in the classical setting, no construction is known to date in the post-quantum setting. We present the first construction of a threshold blind signature secure in the post-quantum setting, based on lattices. We prove its security under an interactive variant of the SIS assumption introduced in [Agrawal et al., CCS’22]. Our construction has a reasonable overhead of a factor of roughly 1.4 X to 2.5 X in signature size over comparable non-threshold blind signatures over lattices under heuristic but natural assumptions.

IEEE Symposium on Security and Privacy (S&P)May 18, 20261 citation

Tanuki: New Frameworks for (Concurrently Secure) Blind Signatures from Post-Quantum Group Actions

Lucjan Hanzlik, Yi-Fu Lai, Marzio Mula +3 more

Lecture notes in computer scienceDec 7, 202510 citations

Post-Quantum Threshold Oblivious Signature

Altana Felixovna Khutsaeva, Sergey Valentinovich Bezzateev

A novel post-quantum threshold oblivious signature scheme is presented. Oblivious signatures enable a requester to obtain a signature on a single selected message from a set of candidates without revealing the selection to the signer. Unlike blind signatures, the signer may be aware of the candidate set. To mitigate single-point failures the scheme employs Shamir’s secret sharing to distribute signing authority among multiple participants. To address quantum threats, it leverages isogeny-based cryptography founded on the Group Action Inverse Problem for post-quantum resilience. The construction adapts an existing isogeny-based oblivious signature by introducing a trusted dealer. The signing protocol is multi-party; verification confirms signature validity on the selected message without revealing secret information. Security reduces to the hardness of Group Action Inverse Problem and the security of the secret-sharing scheme in the semi-honest model, covering corrupted dealers, users, and coalitions of fewer than the threshold number of signers. The threshold design eliminates dependence on a single signer, preventing unauthorized signatures after key compromise. Theoretical contributions advance threshold cryptography with post-quantum primitives; practical applications include anonymous voting, secure transactions, and privacy-preserving distributed systems. Future directions include malicious adversary models and integrations with other post-quantum primitives.

International Scientific-Technical Conference on Actual Problems of Electronic Instrument Engineering (APEIE)Nov 14, 20250 citations

Group Signatures and Accountable Ring Signatures from Isogeny-based Assumptions

Kai-Min Chung, Yao-Ching Hsieh, Mi-Ying Huang +3 more

Group signatures are an important cryptographic primitive providing both anonymity and accountability to signatures. Accountable ring signatures (ARS) combine features from ring signatures (RS) and group signatures (GS), and can be directly transformed into either of both. While there exist extensive works on constructing GS from various post-quantum assumptions, there has not been any research using isogeny-based assumptions. In this work, we propose the first isogeny-based GS, which is a direct result of our isogeny-based ARS. Our schemes are based on the decisional CSIDH assumption (D-CSIDH) and are proven secure under the quantum random oracle model (QROM). This work is also the first post-quantum ARS and GS that are proven QROM-secure.

arXiv:2110.04795Oct 10, 20212 citations