Abstract: A method for distributing electronic files over a network comprising a file combination procedure, a combined electronic file providing procedure, a payment receiving procedure and a main electronic file providing procedure. The file combination procedure combines a main electronic file and an accompanying electronic file into a combined electronic file. The combined electronic file providing procedure provides the combined electronic file to a user before the payment receiving procedure. The payment receiving procedure is a payment procedure that receives the payment from the user for the purchase of the main electronic file. The main electronic file providing procedure provides the user the main electronic file and adds in the main electronic file a watermark for identifying the user. The invention also discloses a corresponding system of distributing electronic files over a network.

Abstract: The present invention provides a cryptosystem for encrypting an original image or voice file by using a camouflaging image or voice file. Each of the original and camouflaging files comprises a plurality of basic units arranged according to a predetermined sequence. The cryptosystem comprises a memory for storing the original and camouflaging files and programs, a processor for executing the programs stored in the memory, and an encrypting program stored in the memory for encrypting the original file by using the camouflaging file.