Image observation on the modified ECB operations in Advanced Encryption Standard

Abstract

This paper presents an image encryption instead of text to observe the modified ECB mode operations in AES processing. If a plaint image contains some groups of identical colors, then the encrypted cipher image may appear some kinds of patterns at the related areas. This is a limitation of AES in ECB mode. To overcome the limitation, a straight forward approach is to make those identical colors different or to remove them. For making those inputs different before encryption, three number sequences, which are the sequential number from counter output, the non-sequential number from accumulator output and the random numbers generated from cipher function itself, are added to the image inputs. By using the different numbers and the different ways of addition, the modifications result in obtaining seven modes of operation, and four of them were defined in NIST publications. To remove the identical inputs, image compression before encryption is used. Though by adding compression and decompression seems to make the whole process more complicated, yet the processing time decreases due to the shrinking file size after image compression. These two approaches to modify ECB operation work very well as shown in the experiments.