US Patent 8086570 Secure document management using distributed hashing

The document management server includes an identification information providing unit that receives a request to obtain identification information required for accessing a document from a client, generates the identification information for the received request, and sends the generated identification information to the client; a relation information management unit that manages relation information of the requested document and the identification information generated for the request; and a history information management unit that manages information on the client who has sent the request, associating with the identification information.