IMAGE ENCRYPTION DEVICE/DECRYPTION DEVICE, IMAGE ENCRYPTION METHOD/DECRYPTION METHOD, AND IMAGE ENCRYPTION PROGRAM/DECRYPTION PROGRAM

摘要

In the encryption processes, some constraints are imposed on the size of an encryption field. For example, when the numbers of divided blocks in the height and width dimensions are respectively divided by a preset positive integer, the size of an encryption field is restricted such that the remainder will be 0 (i.e., the numbers of divided blocks are multiples of positive integers preset for the respective height and width) or a number equal to or larger than 1. In the decryption processes that correspond to the encryption processes above, the block positions in the encryption field are detected according to the constraint on the number of blocks of the encrypted image. As the numbers of blocks are restricted in advance in the height and width dimensions at the time of performing encryption, the numbers of blocks that need to be taken into consideration can be reduced at the time of detecting the block positions. As a result, the precision of decryption improves.