Cryptanalyzing an image encryption algorithm based on scrambling and Veginere cipher

TL;DR

This paper analyzes and improves cryptanalysis methods for an image encryption algorithm based on scrambling and Vigenère cipher, demonstrating vulnerabilities through optimized chosen-plaintext and known-plaintext attacks.

Contribution

It presents an improved chosen-plaintext attack that reduces required plaintexts and reveals vulnerabilities using known-plaintext attacks, enhancing understanding of the cipher's weaknesses.

Findings

Optimized chosen-plaintext attack reduces the number of required plaintexts.

Known-plaintext attack effectively compromises the encryption.

Mathematical and numerical validation of attack effectiveness.

Abstract

Recently, an image encryption algorithm based on scrambling and Vegin`ere cipher has been proposed. However, it was soon cryptanalyzed by Zhang et al. using a combination of chosen-plaintext attack and differential attack. This paper briefly reviews the two attack methods proposed by Zhang et al. and outlines the mathematical interpretations of them. Based on their work, we present an improved chosen-plaintext attack to further reduce the number of chosen-plaintexts required, which is proved to be optimal. Moreover, it is found that an elaborately designed known-plaintex attack can efficiently compromise the image cipher under study. This finding is verified by both mathematical analysis and numerical simulations. The cryptanalyzing techniques described in this paper may provide some insights for designing secure and efficient multimedia ciphers.