Patent ID: 6711553
Filing Date: 2004-03-23
Classification: G06F,G06Q

Abstract:
A method for copy protecting encrypted documents in a client server system using an unsecured communication channel said client server system having at least one client and at least one server for storing encrypted documents, said method including the steps of:receiving an encrypted document from said server by a client; authenticating communications between said client and said server; decrypting by said client said encrypted document using a decryption key when said step of authenticating is successful to derive a decrypted document; preventing storage of said decrypted document on a storage device at any of said at least one client; in response to a user request at said client to save said decrypted document, encrypting said decrypted document with a host specific key associated with said client to provide a re-encrypted document; saving said re-encrypted document in a storage device of said client; selecting, by said at least one server for a positive integer N, a random secret value XN; computing Xn=f(Xn+1), where 1&lE;nissuing said random secret value XN to each of said at least one server and embedding Xn into a module of said client in accordance with said selecting step and said computing step.