International Association for Cryptologic Research

International Association
for Cryptologic Research

CryptoDB

Thorsten Kleinjung

Publications

Year
Venue
Title
2019
ASIACRYPT
CSI-FiSh: Efficient Isogeny Based Signatures Through Class Group Computations
Ward Beullens Thorsten Kleinjung Frederik Vercauteren
In this paper we report on a new record class group computation of an imaginary quadratic field having 154-digit discriminant, surpassing the previous record of 130 digits. This class group is central to the CSIDH-512 isogeny based cryptosystem, and knowing the class group structure and relation lattice implies efficient uniform sampling and a canonical representation of its elements. Both operations were impossible before and allow us to instantiate an isogeny based signature scheme first sketched by Stolbunov. We further optimize the scheme using multiple public keys and Merkle trees, following an idea by De Feo and Galbraith. We also show that including quadratic twists allows to cut the public key size in half for free. Optimizing for signature size, our implementation takes 390 ms to sign/verify and results in signatures of 263 bytes, at the expense of a large public key. This is 300 times faster and over 3 times smaller than an optimized version of SeaSign for the same parameter set. Optimizing for public key and signature size combined, results in a total size of 1468 bytes, which is smaller than any other post-quantum signature scheme at the 128-bit security level.
2017
EUROCRYPT
2015
ASIACRYPT
2014
CRYPTO
2014
ASIACRYPT
2014
CHES
2012
CRYPTO
2012
ASIACRYPT
ECM at Work
Joppe W. Bos Thorsten Kleinjung
2010
CRYPTO
2007
ASIACRYPT
2005
CHES