Patent ID: 7239701

Claim:
A cryptographic communication method for communicating information through a ciphertext between entities, comprising the steps of: generating a secret key of each entity by using mapping at a point on an algebraic curve based on identity information of each entity and secret information; generating at a first entity a first common key by using the secret key of the first entity and a public key obtained by mapping at a point on the algebraic curve based on identity information of a second entity; encrypting at the first entity a plaintext into a ciphertext by using the generated first common key and transmitting the ciphertext to the second entity; generating at the second entity the same second common key as the first common key by using the secret key of the second entity and a public key obtained by mapping at a point on the algebraic curve based on identity information of the first entity; and decrypting at the second entity the transmitted ciphertext into a plaintext by using the generated second common key.