Abstract The development of threshold protocols based on lattice-signature schemes has been of increasing interest in the past several years. The main research focus has been towards protocols constructed for various variants of Crystals-Dilithium, future NIST digital signature standard known as ML-DSA. In this work, we propose TOPCOAT, a two-party lattice-based signature algorithm that embodies Dilithium’s compression techniques. The aforesaid result is achieved by introducing a new hinting mechanism that allows parties to collaboratively calculate $$\textsf {HighBits}$$ HighBits . Our hinting mechanism allows public key compression similar to Dilithium. Additionally, we suggest an optimization technique to minimize number of restarts both parties need to produce a valid signature. Our approach allows to produce $$\approx 10$$ ≈ 10 KB signatures within 3 rounds of communication. We prove security of our scheme under MLWE and MSIS assumptions in ROM, and provide implementation of our proposed scheme. As additional contribution, we present vulnerabilities and inconsistencies found in Liu et al. work (Future Generation Computer Systems 2023) which aimed to construct distributed lattice-based signature protocol.

We present Centralized Attribute Collection Service (CACS), a system for storing credentials in the cloud, with satisfying privacy properties for users, and additional assurances for relying parties. The system deploys privacy-enhancing technologies to protect users’ identities and credentials presented to relying parties. At the same time, the system can vouch for the trustfulness of issuers to relying parties. The system also allows users to obtain the access logs for their credentials, enabling them to compare them against their usage. The presentation of credentials to relying parties follows the standard protocols of Mobile Driving Licence (mDL, ISO 18013-5).

Threshold signatures have gained increased attention especially due to their recent applications in blockchain technologies. In fact, current cryptocurrencies such as Bitcoin, and Cardano started to support multi-signature transactions. Even if the Schnorr-based threshold signatures improve the blockchain's privacy and scalability, these schemes do not provide post-quantum security. In this paper, we propose the optimization of the DS2 lattice-based $(n,n)$-threshold signature scheme and present its practical implementation. Moreover, we evaluate our optimized implementation of the DS2 scheme on different platforms. The results demonstrate that our implementation is easily portable and executable on constrained devices based on ARM Cortex-A53, ARM Cortex-M3, and ESP32 architectures.