Patent ID: 7751558

Claim:
A method for operating an encryption system which provides for operations (a) through (g) defined below, the method being for generating a recipient decryption key RDEC for an entity in the encryption system to enable the entity to act as a recipient which receives and decrypts encrypted digital messages from a message sender, the encryption system including a plurality of authorizers, the plurality of authorizers including at least a root authorizer Au 0 and n lower-level authorizers Au 1 , . . . , Au n in the hierarchy between the root authorizer and the entity, wherein n≧1 the method comprising at least one of operations (Au 0 ), (Au 1 ), . . . (Au n ) each of which is performed or more machines, wherein: the operation (Au 0 ) comprises at least the operations (a), (b); for each i=1, . . . , n, the operation (Au i ) comprises operation (c) and d); and the operations (e), (f), (g) are performed as part of one or more of the operations (Au 0 ), (Au 1 ), . . . , (Au n ); wherein the operations (a) through (g) are as follows: (a) generating a root key generation secret that is known to the root authorizer; (b) generating a root key generation parameter based on the root key generation secret; (c) for each i such that 1≦i ≦n, in the operation (Au i ), generating a lower-level key generation secret for the lower-level authorizer Au i ; (d) for each i such that 1≦i ≦n, in the operation (Au i ), generating a lower-level key generation parameter for the lower-level authorizer Au i , wherein the lower-level key generation parameter is generated using at least the lower-level key generation secret for the lower-level authorizer Au i ; (e) establishing a decryption key generation schedule defining a validity period for the recipient decryption key RDEC for the entity; (f) generating the recipient decryption key RDEC for the entity such that the recipient decryption key RDEC is related to at least the root key generation secret, one or more of the lower-level key generation secrets, and a 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 1; the recipient encryption key RENC is generated using identity information of at least one of the authorizers; each said encrypted digital message is encrypted using a recipient public key RPUB and a recipient encryption key RENC, and is decryptable by the entity using a recipient private key RPRIV and the recipient decryption key RDEC; the recipient public key RPUB and the recipient private key RPRIV form a public key/private key pair 2, wherein the recipient private key RPRIV is a secret of the recipient; (g) dispatching the decryption key to the entity.