The present invention relates to an encryption method for encrypting
information including a series of multiple unit blocks, one at a time, a
decryption method for decrypting multiple encrypted unit blocks, one at a
time, and a recording and reproducing apparatus that uses those methods.
The seed of an encryption key for encrypting each unit block and the seed
of an encryption key for decrypting each encrypted unit block, which are
used by those methods and the recording and reproducing apparatus, are
based on a unit block that is one or more unit blocks before the current
unit block in a reproduction order or on information generated by
encrypting one or more unit blocks before the current unit block.
Alternatively, the seed of an encryption key for encrypting each unit
block and the seed of an encryption key for decrypting each encrypted
unit block are information based on an encryption key for encrypting a
unit block before the current unit block in a reproduction order.