Patent ID: 8645703

Claim:
A method of encrypting a message in a manner that counters power analysis attacks, wherein a long-term private cryptographic key has been selected and a long-term public cryptographic key has been determined based on the long-term private cryptographic key and a base point on a given elliptic curve, the base point having a prime order, the method comprising: determining a modular inverse of the long-term private cryptographic key; generating a sessional private cryptographic key and a sessional public cryptographic key; determining an implicit signature based on the modular inverse of the long-term private cryptographic key, the sessional private cryptographic key, the sessional public cryptographic key and the long-term private cryptographic key; determining a shared secret cryptographic key based on the implicit signature; and encrypting a message using the shared secret cryptographic key; wherein determining the implicit signature comprises evaluating: S A =( k A d A −1 + R A ) d A mod u wherein S A is the implicit signature; k A is the sessional private cryptographic key; d A −1 is the modular inverse of the long-term cryptographic key; d A is the long-term cryptographic key; R A is a function of the sessional public cryptographic key, R A ; and u is the order of the base point.