Strong Non-Transferability from Randomizable Universal Designated Verifier Signatures

In the context of digital certification systems, the demand for privacy-preserving authentication is increasingly vital, particularly for critical applications that involve sensitive personal data. Traditional digital signatures provide a robust means of implementing such systems. However, they raise significant privacy concerns due to their public verifiability, which allows verifiers to prove the authenticity of the received sensitive data to third parties. Universal designated verifier signature (UDVS) schemes address these privacy risks by offering non-transferability, ensuring that only the specified verifier can confirm the validity of the designated verifier signature (DVS). However, despite their advantages, existing UDVS models exhibit vulnerabilities that may allow tracking of the user’s authentications among cooperating verifiers and enable third parties to be convinced of the authenticity of sensitive user data by retrieving DVSs from different, non-cooperating verifiers. This paper presents a strategy to achieve strong non-transferability, which effectively addresses these vulnerabilities, by being the first to extend the concept of randomizability to UDVS schemes and their security properties. Our findings demonstrate that a randomizable UDVS scheme can serve as a solid foundation for constructing strong non-transferable UDVS schemes. Finally, we propose an efficient, strong, non-transferable UDVS scheme as an instantiation of our strategy, utilizing state-of-the-art Type 3 pairings, significantly improving upon previous constructions.