Patent ID: 7841014
Filing Date: 2010-11-23
Classification: G06F,H04L

Abstract:
1. A confidential information processing method for decrypting, in a host system, encrypted content data obtained by encryption of content data with a content key and stored in a target device, the method comprising: the mutual authentication step of performing mutual authentication between the host system and the target device; and the decryption step of, when the mutual authentication has succeeded, decrypting the encrypted content data in accordance with decryption information and the content key by a confidential information processing section, the decryption information indicating a procedure for the decryption of the encrypted content data and relating to contents of an arithmetic operation performed in the decryption of the encrypted content data, wherein in the decryption step, a decryption procedure that is performed in the number of stages selected according to the decryption information is carried out, the decryption procedure being selected from a plurality of decryption procedures including: a two-stage decryption procedure that is performed in two stages, in which the encrypted content data is decrypted with the content key and an encrypted content key obtained by encryption of the content key is decrypted with an intermediate key; and one or more decryption procedures that are performed in three or more stages, wherein in a three-stage decryption procedure that is performed in three stages, the two-stage decryption procedure is performed and an encrypted intermediate key obtained by encryption of the intermediate key is decrypted with a different intermediate key, and in a decryption procedure that is performed in four or more stages, the three-stage decryption procedure is performed and one or more other encrypted intermediate keys obtained by encryption of one or more other intermediate keys are decrypted with one or more still other intermediate keys.