Patent ID: 7155011

Claim:
An encryption method for encrypting information including a plurality of continuous unit blocks having a reproduction order, said plurality of unit blocks being encrypted one unit block at a time, wherein a seed of an encryption key for encrypting a unit block is based on one or more unit blocks that are, in the reproduction order, before the unit block or on information generated by encrypting one or more unit blocks before the unit block, wherein the seed of the encryption key is chained at least twice, wherein an initial value IV of a seed of an encryption key used for encrypting a first unit block of the plurality of unit blocks having the reproduction order is stored, wherein the chain has a plurality of hierarchy levels, a first hierarchy level is encrypted based on the initial value IV of the seed of the encryption key, and a second and higher hierarchy levels are encrypted based on a seed of an encryption key at a lower hierarchy level, wherein, when encrypted unit blocks from the first unit block to any given unit block of the encrypted information are decrypted for reproduction, the initial value IV of the seed of the encryption key that was stored is used, and wherein, when the reproduction of the unit blocks to the given unit block ends, the initial value IV of the seed of the encryption key that was stored is erased and both a seed of an encryption key used for encrypting a unit block follows the given unit block in the reproduction order and a seed of an encryption key used for encrypting a unit block at another hierarchy level after the given unit block are stored.