Digital content encryption / decryption apparatus and method

The disclosed invention is the digital content (Digital Content) In the transmission system for providing a service key information, the user key, temporary valid key using the received transmission to encrypt the digital content, and transmits the digital content encrypted in the user device, the key information and encryption / decryption using the digital content playing and decrypted using the credential screen apparatus and to a method. The present invention is a registered user to the information provider is granted a unique key information, by applying the key information to a key generation algorithm, it generates the user key, and generates when the user requests the digital content after registering the access to the communication temporarily valid key is encrypted by the user key, the digital content is temporarily valid it is transmitted after encrypted by a key, the key information that the user who is provided with a decryption algorithm to be generated is in one-to-one correspondence with the identity characters before purchasing the digital content by ensuring that the supply receiving reproduction and simultaneously decrypt the encrypted digital content, and outputs, when piracy by making it impossible to play back the digital content and to prevent illegal copying and unauthorized distribution.