Patent ID: 7113594

Claim:
In a cryptographic system, a method for sharing an identity-based secret message key between a sender and a receiver, the method comprising: (a) at a private key generator: obtaining an element Q of a first algebraic group, wherein Q represents an identity-based public encryption key of the receiver; computing sQ, where s is an integer representing a secret master key, and where sQ represents a private decryption key of the receiver; sending sQ to the receiver; obtaining an element P of a second algebraic group; computing sP; and sending sP to the sender; (b) at the sender: obtaining the element Q; obtaining the element P; obtaining an element sP from the private key generator; selecting a secret rε ; computing rP; computing the secret message key from r, sP, Q, and a bilinear map; and sending rP to the receiver; (c) at the receiver: obtaining rP from the sender; obtaining sQ from the private key generator; and computing the secret message key from rP, sQ, and the bilinear map.