A Secure and Efficient Implementation of the Quotient Digital Signature Algorithm (qDSA)

Digital signatures provide a means to publicly authenticate messages sent over an insecure channel. Recently, the Quotient Digital Signature Algorithm (qDSA) was introduced aiming key-compatibility with the Diffie-Hellman X25519 function. Due to the novelty of qDSA, there remains a need for an optimized implementation that allows identifying the real impact of this new algorithm. In this work, we focus on the secure and efficient implementation of qDSA. By leveraging the use of precomputation on the right-to-left Joye’s algorithm, we reduced the running time of signature generation by 30-35%, and the running time of the verification procedure by 19%. In addition, for increased security, we show a verification method that validates qDSA signatures unequivocally. All of these improvements were included into an optimized software library targeting 32-bit ARM and 64-bit Intel architectures. The improved performance achieved in these platforms, it positions qDSA as a competitive alternative for deploying digital signatures efficiently and securely.