Identity-based Signatures (IBS) are a form of digital signature scheme that enables the generation and verification of signatures based on a user’s identity, such as an email address, social security number, or any other unique identifier. Recent advancements in post-quantum cryptography have further strengthened IBS schemes, making them resilient against quantum computing threats and ensuring their applicability in future secure communications. At ProvSec’21, Shaw and Dutta introduced an identity-based signature obtained from the isogeny-based signature scheme CSI-FiSh by Beullens et al. at ASIACRYPT’19. Later, at PQCrypto’23, Chen et al. proposed a tightly secure by utilising the tightly secure variant of CSI -FiSh, called Lossy CSI -FiSh, by Kaafarani et al. at PKC’20. In this paper, we generalise those results to obtain a framework for constructing an scheme from cryptographic (non-abelian) group actions. Under the pseudorandom assumption of underlying group actions, we prove that our is tightly secure in the random oracle model. Moreover, we also generalise a Forward-Secure Identity-based Signature (FSIBS) scheme from group actions. This scheme ensures past signatures remain unforgeable even if the current signing key is compromised. Our schemes can be instantiated from existing NIST’s post-quantum signature candidates such as , and .

A traceable ring signature is a variant of ring signatures that allows public traceability of a user's identity if they have produced two signatures for the same issue. Fujisaki and Suzuki first proposed traceable ring signatures at PKC'2007. They have numerous applications in e-coupons, e-voting, and blockchain. While several traceable ring signatures exist in both classical and post-quantum settings, most are proven in the (quantum) random oracle or common reference string models. These models require impractical or inefficient assumptions, such as the heuristic of random oracles or a trusted setup. In this paper, we present the first generic construction of traceable ring signature schemes that do not rely on a trusted setup or the random oracle heuristic. Specifically, our scheme can be instantiated from standard assumptions, and the size of the signatures is only logarithmic in the number of ring members.

Threshold ring signatures (TRS) allow several signers to sign the same message on behalf of a group. This scheme is fully anonymity in that a signature reveals the number of signers who created the signature but tells nothing about the identity of all signers who participated in generating the signature. However, in several scenarios, it is required that signers should take responsibility for their actions and hence traceability of the signer’s identity is needed. In this paper, we introduce a new type of threshold ring signature, called threshold ring signature with accountability (ATRS). It is a balance of anonymity and accountability. In addition to achieving privacy as in the TRS scheme, an ATRS scheme also allows a designated opener to learn the identity of all signers who participated in creating the signature when necessary. Notably, the signers can decide whether they want to disclose their identity if they have any concerns about the designated opener. Moreover, the opener must provide a verifiable opening to ensure that he/she cannot hold a signer responsibility for a signature that was not created by him/her. Our new type of threshold ring signature combines the notion of tracing in traditional anonymity-oriented signature primitives with threshold ring signatures and can enable various new and appealing privacy-preserving applications. We formalise the definition and security requirements for ATRS. We present a generic construction to demonstrate the feasibility of designing ATRS in a modular manner from commonly used cryptographic building blocks (verifiable random function, public-key encryption, pre-constrained encryption and NIWI). Our scheme is secure in the plain model that does not require the heuristic of random oracle or trusted setup assumptions.

The Lattice Isomorphism Problem (LIP) asks whether two given lattices are isomorphic via an orthogonal linear transformation. At Eurocrypt 2022, Ducas and van Woerden provide a solid foundation for LIP as a promising candidate for post-quantum cryptography. They then propose a digital signature HAWK from LIP in the hash-then-sign framework, whose module version was recently investigated by Ducas et al. at Asiacrypt 2022. HAWK is one of the brightest prospects at round one of the NIST for additional digital signatures. In this paper, we build the first (linkable) ring signature schemes based on the hardness of LIP. The proposed signatures have the logarithmic size in the number of ring users. Our signature size is significantly smaller than several ring signatures based on other underlying problems when the number of users in the ring is large. To this end, we leverage group action properties of LIP and follow the Merkle tree-based construction of Beullens, Katsumata and Pintore at Asiacrypt 2020 in the context of isogeny-based cryptography, with suitable adaptions to lattice isomorphism group actions.

Accountable ring signatures close the gap between ring signatures and group signatures. They support a designated opener who can identify signers when necessary while allowing for the most excellent possible flexibility in selecting the ring. Accountable ring signatures were first informally defined by Xu and Yung at CARDIS 2004. They present a compiler that transforms a traditional ring signature scheme into an accountable one by using a trusted model on the smart cards. At ESORICS 2015, Bootle et al. introduced a formal security model for accountable ring signatures. In addition, they also present a generic construction for accountable ring signatures in the random oracle model. In terms of the security proof model, the plain model is preferable since it requires neither any assumptions that sometimes do not exist in practice nor any trusted setup assumptions. Until now, there has been no construction of accountable ring signatures in the plain model, even with a linear signature size. In this paper, we present the first generic construction of accountable ring signature schemes that have the logarithmic signature size and are secure in the plain model using standard assumptions.

Blockchain is a distributed ledger in which a database is distributed across numerous users. Blockchain technologies have recently come to the forefront of the research and industrial communities as they bring potential benefits for many industries. A ring signature is a special type of digital signature which has been widely adopted to protect anonymity and privacy in many cryptocurrencies and blockchain applications. Especially, a unique ring signature offers a special feature enabling the ability to determine whether a signer produces two different ring signatures of the same message with respect to the same ring. The signature size of the previous constructions of unique ring signature is large and grows linearly/sublinearly with the number of ring members. In this paper, we propose a more efficient unique ring signature with logarithmic size. We prove that our scheme is secure under the Decisional Diffie-Hellman and Discrete Logarithm Assumptions, and provide an implementation with a comparison with previous constructions.

Certificateless public key encryption (\(\mathsf {CL}\hbox {-}\mathsf {PKE}\)) solves the problems of establishing public-key infrastructure for traditional public key encryption and resolving key escrow for identity-based encryption. Equality test is an extremely useful property that enables the ability of checking whether two ciphertexts encrypting the same message. Qu et al. (Information Science 2019) introduced the notion of certificateless public key encryption with equality test (\(\mathsf {CL}\hbox {-}\mathsf {PKEET}\)), together with four types of adversaries, that solves certificate manangement and key escrow problems of public key encryption with equality test (\(\mathsf {PKEET}\)) and identity-based encryption with equality test (\(\mathsf {IBEET}\)), and proposed a first \(\mathsf {CL}\hbox {-}\mathsf {PKEET}\) scheme based on Bilinear Diffie-Hellman assumption in random oracle model. In this paper, we propose the first lattice-based \(\mathsf {CL}\hbox {-}\mathsf {PKEET}\) in standard model whose security is reduced to the hardness of the learning with errors problem. In particular, we prove that our schemes are secure against two types of selective-identity adversaries introduced by Qu et al.

Since its birth by Chaum, blind signatures have become one of the fundamental components in the so-called e-cash or e-voting. The scheme ensures a message to be blinded before being signed. Among all lattice-based signatures submitted to NIST post-quantum cryptographic standardization, Dilithium is a very promising candidate. The scheme has some advantages such as simple to implement securely, conservative with parameters and minimal in total size of public key and signature. In this paper, we propose a blind signature scheme based on the framework of Dilithium in order to take advantages of Dilithium. The proposed scheme is blind and one-more unforgeable secure in the random oracle model under the hardness of the module Learning with Errors problem MLWE and the module short integer solution problem MSIS.

In 2012, Tim Güneysu, et al. proposed the GLP signature scheme, a practical and efficient post-quantum signature scheme. It is built on the modification of Vadim Lyubashevsky’s idea of constructing previous signature schemes. It has a significantly smaller signature and key size than prior signature scheme. The design of the GLP is a foundation to construct newer signature schemes such as Bai-Galbraith, Dilithium. However, Tim Güneysu has only given the description of the GLP signature scheme that has not yet given a detailed security proof for this scheme. Therefore, in this paper, we will present a full security proof for the GLP signature scheme. Specifically, we show that the GLP signature scheme is EU-CMA secure in the random oracle model.