What is SQIsign?

SQIsign is an isogeny-based digital signature scheme in which the secret key is a hidden isogeny between supersingular elliptic curves and a signature is a proof of knowledge of that isogeny, constructed through the correspondence between isogenies and ideals in quaternion orders. It produces signatures and public keys far more compact than lattice-based or hash-based alternatives, at the cost of substantially heavier signing and verification computation.