Electronic data protection system

An electronic data protection system for protecting electronic data from illegal copying by a third party, comprising:

• at least one storage medium for storing encrypted electronic data, a medium personal number which is unique for each storage medium and encrypted permission information;
• a vendor computer having a personal key generating means for generating a medium key based on the medium personal number, an electronic data decrypting key, and an encrypting means for encrypting the electronic data decrypting key based on the medium key to generate the encrypted permission information;
• and
• a user computer having a personal key generating means for generating a medium key based on the medium personal number, a first decrypting means for decrypting the encrypted permission information based on the medium key to generate the electronic data decrypting key which is the same as the electronic data decrypting key of the vendor computer, and a second decrypting means for decrypting the encrypted electronic data based on the electronic data decrypting key to generate a plain text electronic data wherein the vendor computer writes the medium personal number onto the storage medium in an un-rewritable form which the user computer cannot rewrite.