Patent ID: 6266421
Filing Date: 2001-07-24
Classification: H04L

Abstract:
A key recovery control unit in which an encrypted message obtained by encrypting a data key serving as a data encryption/decryption key with a system key serving as a data encryption key is decrypted by using a master key serving as a data decryption key in accordance with a user's request, thereby recovering the data key, comprising:acquisition means for acquiring, from a suer, a first encrypted message obtained by encrypting a first data key with a first system key, and a second encrypted message obtained by encrypting a second data key with a second system key, which is added with data obtained by encrypting a key recovery field on a recovery condition of the first data key with the second data key;first key recovery means for decrypting the second encrypted message acquired in said acquisition means by a master key which is paired with the second system key, thereby recovering the second data key, and decrypting the encrypted message of the key recovery field added to the second encrypted message by using the second data key, thereby recovering the key recovery field;field authorization check means for checking, according to a recovery condition specified by the key recovery field recovered by said first key recovery means, whether the user supplying the first encrypted message and the second encrypted message has a recovery authorization of the first data key; andsecond key recovery means for decrypting the first encrypted message acquired in said acquisition means by using a master key paired with said first system key if it is judged in said fist authorization check means that the user has the recovery authorization, thereby recovering the first data keys whereinthe data obtained by encrypting the key recovery field with the first data key is added to the first encrypted message, and said second key recovery means decrypts the first encrypted message obtained by said acquisition means with a master key paired with said first system key to recover the first data key if it is judged in said first authorization means that the user has the recovery authorization, and decrypts the encrypted message of the key recovery field added to the first encrypted message with the first data key to recover the key recovery field, and whereinsaid key recovery control unit further comprises second authorization check means for checking whether the key recovery field recovered in said first key recovery means is coincident with the key recovery field recovered in said second key recovery means, and means for supplying said first data key recovered by said second key recovery means to the user concerned only when it is judged that the key recovery field recovered by said first key recovery means is coincident with the key recovery field recovered by said second key recovery means.