Abstract: A content copying device has a mutual authentication section that performs a mutual authentication with a copy source recording medium and a copy destination recording medium respectively and generates a first medium unique key and a second medium unique key, a content key decrypting section that reads an encrypted content key from the copy source recording medium, and decrypts the encrypted content key using information based on the first medium unique key, a content key encrypting section that encrypts the decrypted content key using information based on the second medium unique key and writes the encrypted content key onto the copy destination recording medium, and a content copying section that reads an encrypted content from the copy source recording medium and writes the content onto the copy destination recording medium without performing decryption.

Abstract: An image data compressing apparatus includes an image data compressor for compressing image data input thereto at first and second compression rates to produce first and second compressed data, respectively, an approximate-expression selector having an approximate-expression table including approximate expressions corresponding to sample data sizes, respectively, and a compression rate determining unit for determining the second compression rate. The approximate-expression selector selects an approximate expression from the approximate expressions. The first approximate expression corresponds to a first sample data size nearest a data size of the first compressed data among the sample data sizes. Each of the approximate expressions indicates a change of a data size in response to a compression rate. The compression rate determining unit determines the second compression rate based on the selected approximate expression.

Abstract: A content copying device has a mutual authentication section that performs a mutual authentication with a copy source recording medium and a copy destination recording medium respectively and generates a first medium unique key and a second medium unique key, a content key decrypting section that reads an encrypted content key from the copy source recording medium, and decrypts the encrypted content key using information based on the first medium unique key, a content key encrypting section that encrypts the decrypted content key using information based on the second medium unique key and writes the encrypted content key onto the copy destination recording medium, and a content copying section that reads an encrypted content from the copy source recording medium and writes the content onto the copy destination recording medium without performing decryption.

Abstract: A recording device has a content encryption unit for writing a content encrypted with a content key in a recording medium, and a key encryption unit for encrypting the content key and writing the encrypted content key in the recording medium. A content key processing device has a key decryption unit that decrypts the content key that has been encrypted and recorded in a recording medium, and a key encryption unit that re-encrypts the decrypted content key with predetermined information and writes the re-encrypted content key in the recording medium.

Abstract: An image data compressing apparatus includes an image data compressor for compressing image data input thereto at first and second compression rates to produce first and second compressed data, respectively, an approximate-expression selector having an approximate-expression table including approximate expressions corresponding to sample data sizes, respectively, and a compression rate determining unit for determining the second compression rate. The approximate-expression selector selects an approximate expression from the approximate expressions. The first approximate expression corresponds to a first sample data size nearest a data size of the first compressed data among the sample data sizes. Each of the approximate expressions indicates a change of a data size in response to a compression rate. The compression rate determining unit determines the second compression rate based on the selected approximate expression.