An encryption/decryption system capable of supplying data only to a user making a request. A computer encrypts data with a common key, encrypts the common key with a public key, and transmits the encrypted data and the encrypted common key. A copy machine receives these data, encrypts challenge data...http://www.google.de/patents/US7526656?utm_source=gb-gplus-sharePatent US7526656 - Encryption/decryption system and method for the same
