Patent ID: 7257709

Claim:
A method of validating a public key in an elliptic curve cryptosystem using an elliptic curve over a finite field, the public key comprising two coordinates (x,y) where x and y are elements of said finite field, said elliptic curve having cofactor h and said finite field being a binary field, said method comprising the steps of: a) receiving the public key; b) applying a function to the public key to obtain a result, the function being an algebraic expression and having for each order of the elliptic curve a predefined value for points on the elliptic curve of that order, whereby a characteristic of the public key is verifiable based on the order of the result; c) comparing the result of the function to predetermined information to determine the acceptability of the order of the result in order to determine the validity of the public key; and d) partially validating said public key if the order of the result is acceptable.