Method for the application of implicit signature schemes

A certifying authority for enabling a transaction between a first and second correspondent over a data communication system to be verified, said certifying authority having control of a public key's validity, said public key being used by at least said first correspondent, said certifying authority comprising a cryptographic unit configured for:

• a) receiving from one of said first and second correspondents, a request that said public key be validated;
• b) verifying the validity of said public key attributed to said first correspondent;
• c) generating implicit certificate components including a first component comprising transaction specific information particular to said request in step a), a second component computed using said public key of said first correspondent, and a third component computed from said first and second components and a private key of said certifying authority;
• d) having forwarded to said first correspondent, at least said third component of said implicit certificate components for permitting said first correspondent to generate a transaction specific private key using said third component;
• and
• e) having forwarded to said second correspondent at least said first and second components of said implicit certificate components for permitting recovery of a transaction specific public key corresponding to said transaction specific private key using said first and second components and a public key of said certifying authority;
• wherein said first correspondent can sign a message with said transaction specific private key, forward said message to said second correspondent, and said second correspondent can attempt to verify said message using said transaction specific public key to proceed with said transaction upon verification.