Patent ID: 7228568

Claim:
A method for recording encrypted content data selected from among a plurality of pieces of encrypted content data recorded from a primary recording medium to a secondary recording medium which is different from said primary recording medium, said method comprising the steps of: firstly, receiving an enabling key block of a first piece of encrypted content data for restoring a root key of a hierarchical key group transmitted from said primary recording medium; searching for said root key by use of said enabling key block; receiving an encrypted content key associated with said first piece of encrypted content data; secondly, receiving said first piece of encrypted content data from said primary recording medium after the searching for said root key; decrypting said first piece of encrypted content data received in said second receiving step; recording the first piece of content data decrypted in said decrypting step to said secondary recording medium; determining, if an additional and subsequent piece of encrypted content data is transferred from said primary recording medium to said secondary recording medium, whether an enabling key block of said additional and subsequent piece of encrypted content data is common to an enabling key block of said first piece of encrypted content data; and transferring only said additional and subsequent piece of encrypted content data and encrypted content key to said secondary recording medium, if it is determined that the enabling key block of said additional and subsequent piece of encrypted content data is common to said enabling key block of said first piece of encrypted content data.