Patent ID: 7324974

Claim:
A digital data playing device for reproducing a digital data file, comprising: a data storage medium for storing the digital data file transferred from a source device, the digital data file having been encrypted by: 1) generating a key data using at least a unique ID of the digital data playing device or a unique ID of the storage medium or both; 2) transmitting said key data from the digital data playing device to a unit of the source device through a network; and 3) encrypting within the source device the digital data file using said key data; and a decoding unit configured to decrypt the digital data file read from the data storage medium using said key data, wherein said key data is generated by: summing one or more first internal keys to the unique ID of the digital data device or the unique ID of the storage medium or both to generate an internal encryption key; and generating said key data by converting the internal encryption key according to an encryption algorithm using a second internal key.