Patent ID: 8024583

Claim:
A host device for processing confidential information, which reads an encrypted content from a target device storing encrypted confidential information that includes the encrypted content, and decrypts the encrypted content for use, the host device comprising: a confidential information processor performing operations according only to a plurality of predetermined sequences; a Central Processing Unit (CPU) which directs said confidential information processor to initiate the sequences; a first interface which inputs and outputs data including the confidential information between said confidential information processor and the target device; and a second interface which inputs and outputs data including the confidential information between said confidential information processor and said CPU, wherein: m+1 keys {K 0 , K 1 , . . . , Km} are stored, as the encrypted confidential information, in the target device or said host device; n keys {Kb 1 , . . . , Kbn} are stored in the target device or a different target device, n being a natural number; the key Km is a content key for encrypting a content; the key Ki is encrypted with a key K (i−1), i being a natural number satisfying 1≦i≦m; the sequences include a key conversion sequence which converts a Ki encrypted with a K (i−1) into a Ki encrypted with a key different from the K (i−1), the to-be-converted encrypted Ki being a key of the encrypted m+1 keys; said host device further performs an authentication processing for the target device or the different target device; a key Kb 0 is an authentication key generated by the authentication processing; the different key is a key of the keys {Kb 0 , . . . , Kb (n−1)}; and said first interface and said second interface output the confidential information outside said confidential information processor, only when the confidential information is encrypted, after the key conversion sequence is initiated.