# Universal chosen-ciphertext attack for a family of image encryption schemes

## TL;DR

This paper reveals a universal vulnerability in a class of image encryption schemes using permutation and modular addition, demonstrating that plaintexts can be reconstructed via chosen-ciphertext attacks without the key.

## Contribution

The paper introduces a universal chosen-ciphertext attack method applicable to a class of image ciphers, showing their fundamental linearity and security weaknesses.

## Key findings

- Plaintexts can be reconstructed without keys.
- The attack exploits linear differential mappings.
- Security of certain image encryption schemes is compromised.

## Abstract

During the past decades, there is a great popularity employing nonlinear dynamics and permutation-substitution architecture for image encryption. There are three primary procedures in such encryption schemes, the key schedule module for producing encryption factors, permutation for image scrambling and substitution for pixel modification. Under the assumption of chosen-ciphertext attack, we evaluate the security of a class of image ciphers which adopts pixel-level permutation and modular addition for substitution. It is mathematically revealed that the mapping from differentials of ciphertexts to those of plaintexts are linear and has nothing to do with the key schedules, permutation techniques and encryption rounds. Moreover, a universal chosen-ciphertext attack is proposed and validated. Experimental results demonstrate that the plaintexts can be directly reconstructed without any security key or encryption elements. Related cryptographic discussions are also given.