International Association
for Cryptologic Research

We describe a tight security reduction to the discrete logarithm problem for KCDSA under an extended Random Oracle Model. This is achieved by generalising the signature scheme and producing a security proof for the generalised scheme. We require the application of Randomized Hashing. We also introduce a Challenger to the Random Oracle Model, who is external to the Simulator and Adversary. The Challenger provides oracle returns for one hash function, and challenges which have a low probability of being met. On presentation of a forged signature the Simulator either identifies an edge case which allows solving of a challenge, or solves the discrete logarithm problem. Hence the tight reduction.