We introduce a special class of supersingular curves over
,
characterized by the existence of noninteger endomorphisms of small degree. We prove
a number of properties about this set. Most notably, we can partition this set into
subsets such that curves within each subset have small-degree isogenies between them,
but curves in distinct subsets have no small-degree isogenies between them.
Despite this, we show that isogenies between distinct subsets can heuristically
be computed efficiently, giving a technique for computing isogenies between
certain prescribed curves that cannot be efficiently found by searching on
-isogeny
graphs.
Keywords
supersingular, elliptic curve, isogeny graph, M-small,
endomorphism, quaternion, maximal order, Deuring
correspondence, partition, archipelago, island, airport,
orientation, Hilbert class polynomial