BEGIN:VCALENDAR VERSION:2.0 PRODID:researchseminars.org CALSCALE:GREGORIAN X-WR-CALNAME:researchseminars.org BEGIN:VEVENT SUMMARY:Toshiyuki Katsura (University of Tokyo) and Katsuyuki Takashima (M itsubishi Electric) DTSTART:20200630T001000Z DTEND:20200630T004000Z DTSTAMP:20260423T195930Z UID:ANTS14/4 DESCRIPTION:Title: C ounting Richelot isogenies between superspecial abelian surfaces\nby T oshiyuki Katsura (University of Tokyo) and Katsuyuki Takashima (Mitsubishi Electric) as part of Algorithmic Number Theory Symposium (ANTS XIV)\n\n\n Abstract\nCastryck\, Decru\, and Smith used superspecial genus-2 curves an d their Richelot isogeny graph for basing genus-2 isogeny cryptography\, a nd recently\, Costello and Smith devised an improved isogeny path-finding algorithm in the genus 2 setting. In order to establish a firm ground for the cryptographic construction and analysis\, we give a new characterizati on of decomposed Richelot isogenies in terms of involutive reduced automor phisms of genus-2 curves over a finite field\, and explicitly count such d ecomposed (and non-decomposed) Richelot isogenies between superspecial pri ncipally polarized abelian varieties. As a corollary\, we give another alg ebraic geometric proof of Theorem 3 in the paper of Castryck et al.\n\nCha irs: Brendan Creutz and Felipe Voloch\n LOCATION:https://researchseminars.org/talk/ANTS14/4/ END:VEVENT END:VCALENDAR