| 摘要 |
A trusted authority 63 is provided for identity-based cryptography. The trusted authority 63 has a secret x and derives first and second elements g, y. At least the second element is made public. The first element is calculated as a cryptographic hash of an identifier IDTA associated with the trusted authority (step 2). The second element is a combination of the first element and the secret x (step 4). The trusted authority 63 provides a private-key generation service to a third party 62 who is the recipient of an encrypted message J. A private keys h<zx> is calculated (steps 15 and 16) in dependence on the secret x and an identifier string (STR) associated with the third party. Preferably the invention is El-Gamal based. The invention may not be based on bilinear maps. A Bilinear map embodiment is disclosed in GB 2401763 and GB 2390515. |
