Patent ID: 7457419

Claim:
An information processing method for encrypting encoded data generated by multi-stage wavelet transformation of image data, the method comprising the steps of: dividing sub-bands of a plurality of resolution levels in the encoded data into a plurality of rectangular regions; defining a plurality of groups, wherein each group includes an aggregation of encoded data of a plurality of rectangular regions having a same position in two-dimensional space of sub-bands of a same resolution level; defining a tree structure that includes a plurality of nodes corresponding to the groups, where each node of the plurality of nodes is classified according to a first criterion of position in two-dimensional space and a second criterion of resolution level, and where nodes, from among the plurality of nodes, classified according to the first criterion are positioned according to the second criterion such that higher-resolution nodes are positioned above lower-resolution nodes; determining whether each node is arranged in accordance with either the first criterion or the second criterion: generating node keys corresponding to respective ones of the plurality of nodes in the tree structure in order from a highest node to a lowest node, using an encryption key assigned to the highest node, wherein the node keys for each node classified according to the first criterion determined in said determining step are generated based on a one-way function to which an encryption key assigned to a higher node than the node in question and information associated with a corresponding rectangular region are used as arguments, while node keys for each node classified according to the second criterion determined in said determining step are generated based on the one-way function to which an encryption key assigned to the higher node than the node in question is used as an argument; encrypting each group of each node using a corresponding generated node key; and outputting information associated with the generation of the node keys for each of the groups, wherein the information outputted in said outputting step includes information indicating whether node keys for each node are generated based on the one-way function to which an encryption key assigned to the higher node than the respective node in question and information associated with a corresponding rectangular region are used, or based on the one-way function to which an encryption key assigned to the higher node than the node in question is used.