Cryptanalyzing an image encryption algorithm based on autoblocking and electrocardiography

TL;DR

This paper critically examines the security of a specific image encryption algorithm based on ECG signals and autoblocking, revealing vulnerabilities to known plaintext attacks and highlighting broader security issues in similar schemes.

Contribution

It provides a detailed cryptanalysis of the Ye-Huang algorithm, exposing its weaknesses and offering insights applicable to other image encryption methods.

Findings

Vulnerable to known plaintext attack

Able to derive an effective decryption mask

Highlights security flaws in similar encryption schemes

Abstract

This paper analyzes the security of an image encryption algorithm proposed by Ye and Huang [\textit{IEEE MultiMedia}, vol. 23, pp. 64-71, 2016]. The Ye-Huang algorithm uses electrocardiography (ECG) signals to generate the initial key for a chaotic system and applies an autoblocking method to divide a plain image into blocks of certain sizes suitable for subsequent encryption. The designers claimed that the proposed algorithm is "strong and flexible enough for practical applications". In this paper, we perform a thorough analysis of their algorithm from the view point of modern cryptography. We find it is vulnerable to the known plaintext attack: based on one pair of a known plain-image and its corresponding cipher-image, an adversary is able to derive a mask image, which can be used as an equivalent secret key to successfully decrypt other cipher-images encrypted under the same key with a non-negligible probability of 1/256. Using this as a typical counterexample, we summarize security defects in the design of the Ye-Huang algorithm. The lessons are generally applicable to many other image encryption schemes.