Patent ID: 7463736

Claim:
A data processing method comprising: an encoding step of encoding image data into a plurality of bit streams arranged in ascending order of resolution levels; a first key generation step of generating a plurality of keys for respective resolution levels of the encoded image data, the first key generation step generating a key for the highest resolution level by converting a basic key with a predetermined function and generating respective keys for other resolution levels by repetitively converting a key for a preceding resolution level with the predetermined function; an encryption step of encrypting each of the bit streams using a corresponding one of the plurality of keys; a delivery step of delivering all of the encrypted bit streams in ascending order of resolution levels to a user with a key for a predetermined resolution level corresponding to the user; a second key generation step of generating respective keys for resolution levels under the predetermined resolution level by repetitively converting the key for the predetermined resolution level with the predetermined function; and a decryption step of sequentially applying the keys generated in the second key generation step in order of generation to the delivered bit streams in order of delivery, thereby decrypting the encrypted bit stream in the predetermined resolution level using the key for the predetermined resolution level and decrypting the encrypted bit stream in each of resolution levels under the predetermined resolution level using the respective keys.