Digital data file encryption apparatus and method

An electric reproducing device for decrypting content, the electric reproducing device comprising:

• a receiver;
• a decoder;
• an output unit;
• and
• a processor configured to control the electric reproducing device to:
• receive the content, through the receiver, without a source encryption key from a source device connected to the electric reproducing device, the content having been encrypted with the source encryption key in the source device, wherein the source device is configured to perform an authenticating operation with the electric reproducing device by using an identifier (ID) associated with at least one of the electric reproducing device and a storage medium of the electric reproducing device,
• perform a first addition operation by using a first device internal key and the ID, the first device internal key being associated with the electric reproducing device,
• generate a device encryption key based on an output of the first addition operation and a second device internal key by using a predetermined encryption algorithm, wherein the second device internal key is associated with the electric reproducing device,
• decrypt the content using the device encryption key, wherein the source encryption key is identical to the device encryption key, the source encryption key being independently generated in the source device,
• control the decoder to decode the decrypted content, and
• output the decoded content through the output unit.