Security of new encryption algorithm for image cryptosystems

Abstract

To keep transmitted messages secret, straightforward encryption is an effective method. Taking efficiency into account, recently partial encryption has become widely accepted for images, audio and video. However, a new efficient approach is required in cases where a large number of images are intentionally transmitted to the same destination. An encryption algorithm for images based on vector quantization was proposed by Chang, Hwang and Chen, in which encrypting a common codebook is suggested to be the better choice of their two proposed schemes, because many images can be transmitted with only one encrypted corresponding codebook. However, in the present paper, the vulnerability of the CHC image cryptosystem is found according to the chosen-plainimage attack if the common codebook is used to encrypt a large number of images. And based on the cipherimage-only attack, keeping the index sets in a clear form is shown not to be a good idea. Accordingly, a way of securing the transmitted images is recommended.

Keywords:

• IMAGE ENCRYPTION
• VECTOR QUANTIZATION
• IMAGE CRYPTOSYSTEM
• CHOSEN-PLAINIMAGE ATTACK
• CIPERIMAGE-ONLY ATTACK