Patent ID: 7443980

Claim:
A computer-implemented encryption method for encrypting a message M for decryption with secret information of an intended recipient entity E which is to use secret information obtained using a value or values generated by one or more of E's parents in a hierarchical cryptographic scheme, the method comprising: (1) generating variable data including a variable value r; (2) forming a first encryption of the message M, wherein the first encryption is decryptable without using E's secret information but using a value g r , where g=ê ( p 0 ,p 1 ), ê:G 1 ×G 1 →G 2 is a non-degenerate bilinear mapping, where G 1 and G 2 are groups, where ê, G 1 , G 2 are pre-defined to be independent of M; p 0 is pre-defined to be independent of M and of E's ID, and P 1 is independent of E's ID but depends on ID's of one or more of E's parents; (3) forming a first ciphertext portion dependent on E's ID, wherein the first ciphertext portion is formed as a function of one or more inputs including the variable data and E's ID but not including E's secret information, but the value g r is computable as a function of one or more inputs including the first ciphertext portion and E's secret information; (4) outputting a ciphertext formed using the first ciphertext portion and the first encryption of the message M.