Patent ID: 7657748

Claim:
A method for operating a public-key encryption scheme which provides for sending a digital message M between a sender and a recipient with participation of an authorizer, wherein the digital message is encrypted by the sender and decrypted by the recipient, the method comprising encrypting, by at least one machine in a set of one or more machines, the digital message M using at least a recipient public key RPUB and a recipient encryption key RENC to create an encrypted digital message for decryption with a recipient private key RPRIV and a recipient decryption key RDEC, wherein: the recipient public key RPUB and the recipient private key RPRIV form a public key/private key pair 1 , wherein the recipient private key RPRIV is a secret of the recipient; the recipient decryption key RDEC is generated using at least a key generation secret of the authorizer and the recipient encryption key RENC, wherein a key formed from the recipient encryption key RENC and a key formed from the recipient decryption key RDEC are a public key/private key pair 2 ; wherein the recipient decryption key RDEC is generated by the authorizer to have a value S=s c P B , wherein: s c is the key generation secret of the authorizer; and P B is the recipient encryption key RENC and is equal to H 1 (Inf B ), wherein Inf B is an element of a first cyclic group G 1 of elements, wherein P B is an element of a second cyclic group G 2 of elements, and H 1 is a predefined function (“first function H 1 ”), wherein the first and second cyclic groups G 1 and G 2 and the function H 1 are system parameters made available to the sender, and also available to the sender are system parameters comprising: a generator P of the first cyclic group G 1 ; a key generation parameter Q=s c P; a second function H 2 capable of generating a second string of binary digits from an element of the second cyclic group G 2 , wherein Inf B comprises the identity of the recipient, ID rec , the recipient public key RPUB, and a parameter defining a validity period for the recipient decryption key RDEC.