On oriented supersingular elliptic curves

Abstract

We revisit theoretical background on OSIDH, that is an isogeny-based key-exchange protocol proposed by Col\`o and Kohel at NutMiC 2019. We give a proof of a fundamental theorem for OSIDH. The theorem was stated by Col\`o and Kohel without proof. Furthermore, we consider parameters of OSIDH, give a sufficient condition on the parameters that the protocol works, and estimate the size of the parameters for a certain security level.