Patent ID: 7590238

Claim:
A system comprising a plurality of first communication apparatuses and a managing apparatus that performs cryptographic communication between the first communication apparatuses and a plurality of external second communication apparatuses, wherein the managing apparatus comprises: a key storing section that stores a plurality of first cryptographic keys shared by the managing apparatus and at least one of the second communication apparatuses, respectively, in order to selectively enable at least one of a plurality of second communication apparatuses to decrypt encrypted data broadcasted to the plurality of second communication apparatuses, a key generating section that receives an input designating a second communication apparatus among the plurality of second communication apparatuses to be enabled to decrypt encrypted data broadcast by one of the first communication apparatuses that has requested to delegate an authority of encryption communication, reads the first cryptographic key shared with the specified second communication apparatus from the key storing section; performs a computation by passing the stored first cryptographic key to the keyed one-way function, and generates, as second cryptographic keys, a computed result; and a key outputting section that outputs the second cryptographic keys and a key of the one-way function to the first communication apparatus that has requested to delegate an authority of encryption communication, and the first communication apparatus that has requested to delegate an authority of encryption communication to the managing apparatus comprises: a key generation controlling section that transmits to the second communication apparatus, the key of the one-way function received from the managing apparatus, and which thereby causes the second communication apparatus to perform computation by passing the stored first cryptographic key to the keyed one-way function, and thus to generate a second cryptographic key; and a cryptographic communication section that performs the cryptographic communication with the specified second communication by encrypting data by the second cryptographic key received from the managing apparatus.