Patent ID: 7827416

Claim:
A key management apparatus comprising: an encryption key memory that stores an encrypted document identifier of an encrypted document and a first encryption key, the first encryption key being configured for use in decoding the encrypted document, the encrypted document identifier and the encryption key corresponding to each other; and one or more computer processors programmed to execute: a user group determining function that determines the usage rights of users for the encrypted document, a usage rights issuing function that, in response to receiving a read request using the encrypted document identifier transmitted from a remote terminal by a user who is determined to have usage rights to read the encrypted document by the user group determining function, performs the following: refers to the encryption key memory and a usage rights set memory, wherein the usage rights memory stores the usage rights for the encrypted document in correspondence with the encrypted document identifier, and sends the usage rights corresponding to the encrypted document identifier and the first encryption key to the remote document terminal from which the read request is received, and an encryption information issuing function that, in response to receiving an edit request using the encrypted document identifier transmitted from a remote terminal by a user who is determined to have usage rights to edit the encrypted document by the user group determining function, performs the following: refers to the encryption key memory and the usage rights set memory, instructs to generate an identifier of a document to be encrypted, instructs to generate a second encryption key, the second encryption key being different than the first encryption key, stores the generated identifier and the second encryption key in the encryption key memory and the usage rights set memory, respectively, and sends the generated identifier, the first encryption key, and the second encryption key to the remote terminal from which the edit request is received, wherein: the edit request is a request to edit the encrypted document, and the second encryption key is configured for use by the remote terminal from which the edit request is received to encrypt a document generated as a result of: decoding the encrypted document, and editing the decoded document.