DiLizium 2.0: Revisiting Two-Party Crystals-Dilithium

In previous years there has been an increased interest in designing threshold signature schemes. Most of the recent works focus on constructing threshold versions of ECDSA or Schnorr signature schemes due to their appealing usage in blockchain technologies. Additionally, a lot of research is being done on cryptographic schemes that are resistant to quantum computer attacks. In this work, we propose a new version of the two-party Dilithium signature scheme. The security of our scheme is based on the hardness of Module-LWE and Module-SIS problems. In our construction, we follow a similar logic as Damgård et al. (PKC 2021) and use an additively homomorphic commitment scheme. However, compared to them, our protocol uses signature compression techniques from the original Dilithium signature scheme which makes it closer to the version submitted to the NIST PQC competition. We focus on two-party signature schemes in the context of user authentication

Russian Federal Remote E-voting Scheme of 2021 -- Protocol Description and Analysis

This paper presents the details of one of the two cryptographic remote e-voting protocols used in the Russian parliamentary elections of 2021. As the official full version of the scheme has never been published by the election organisers, our paper aims at putting together as complete picture as possible from various incomplete sources. As all the currently available sources are in Russian, our presentation also aims at serving the international community by making the description available in English for further studies. In the second part of the paper, we provide an initial analysis of the protocol, identifying the potential weaknesses under the assumptions of corruption of the relevant key components. As a result, we conclude that the biggest problems of the system stem from weak voter authentication. In addition, as it was possible to vote from any device with a browser and Internet access, the attack surface was relatively large in general

Server-Supported Decryption for Mobile Devices

We propose a threshold encryption scheme with two-party decryption, where one of the keyshares may be stored and used in a device that is able to provide only weak security for it. We state the security properties the scheme needs to have to support such use-cases, and construct a scheme with these properties

DiLizium: A Two-Party Lattice-Based Signature Scheme

In this paper, we propose DiLizium: a new lattice-based two-party signature scheme. Our scheme is constructed from a variant of the Crystals-Dilithium post-quantum signature scheme. This allows for more efficient two-party implementation compared with the original but still derives its post-quantum security directly from the Module Learning With Errors and Module Short Integer Solution problems. We discuss our design rationale, describe the protocol in full detail, and provide performance estimates and a comparison with previous schemes. We also provide a security proof for the two-party signature computation protocol against a classical adversary. Extending this proof to a quantum adversary is subject to future studies. However, our scheme is secure against a quantum attacker who has access to just the public key and not the two-party signature creation protocol