Patent ID: 7146009

Claim:
A method for secure communication of a message M between a sender and a recipient, with the assistance of a key server, the method comprising: the sender obtaining a symmetric key Ks and encrypting the message M with the symmetric key Ks thereby forming an encrypted message Me; the sender encrypting the symmetric key Ks with a public encryption key Ke associated with the recipient thereby forming an encrypted symmetric key Kse; the sender forming first and second split-key fragments Kse 1 and Kse 2 , respectively, from the encrypted symmetric key Kse; the sender sending the second split-key fragment Kse 2 to the key server; the key server storing decryption key information, wherein the decryption key information is formed from the second split-key fragment Kse 2 , and wherein the decryption key information comprises information needed by the recipient to form a decryption key suitable for decrypting the encrypted message Me, the sender obtaining the key retrieval information Kr, wherein Kr is necessary to permit the recipient to retrieve decryption key information from the key server; the sender transmitting to the recipient the encrypted message Me, the first split-key fragment Kse 1 and the key retrieval information Kr; the recipient transmitting the key retrieval information Kr to the key server and receiving the decryption key information in response thereto; the recipient forming the encrypted symmetric key Kse from the first split-key fragment Kse 1 and Kse 2 , Kse 2 being derived from the decryption key information; the recipient decrypting the encrypted symmetric key Kse with a private decryption key Kd of the recipient thereby forming the symmetric key Ks; and the recipient derypting the encrypted message Me with the symmetric key Ks to read the original message M.