On Lions and Elligators: An efficient constant time implementation of CSIDH
The recently proposed CSIDH primitive is a promising candidate for post quantum static static key exchanges with very small keys. However, until now there is only a variable time proof of concept implementation by Castryck, Lange, Martindale, Panny, and Renes, recently optimized by Meyer and Reith, which can leak various information about the private key. Therefore, we present an efficient constant time implementation that samples key elements only from intervals of nonnegative numbers and uses dummy isogenies, which prevents certain kinds of side channel attacks. We apply several optimizations, e.g. Elligator and the newly introduced SIMBA, in order to get a more efficient implementation.
IACR Cryptol. ePrint Arch.