Enhanced Image Encryption using Chaotic Substitution, DNA Encoding, and Random Permutation

Abstract

With the increasing challenges of securing multimedia transmission over the internet, image encryption has emerged as a critical research area. This paper presents a novel image encryption scheme that integrates chaotic substitution, DNA encoding, and random permutation techniques to enhance security. The proposed method exploits the unpredictability of chaotic sequences, the computational benefits of DNA encoding, and the randomness of permutation to strengthen encryption.In this approach, pixel values are initially converted into DNA sequences using a predefined encoding scheme. A high-dimensional Lorenz chaotic map generates chaotic sequences, which are then employed for pixel substitution, effectively scrambling the DNA-encoded pixel values. Furthermore, a random permutation technique known as the Fisher-Yates shuffle is applied to further disrupt the substituted pixel values, increasing the overall complexity of the encryption process.By integrating these techniques, the proposed scheme achieves robust security, making it resistant to various cryptographic attacks. Experimental results validate the effectiveness of this approach, demonstrating high encryption strength while maintaining computational efficiency.

Introduction

1. Importance of Image Encryption
Image encryption is vital for protecting the confidentiality and integrity of digital images in fields like photography, medical imaging, and satellite data. It transforms visual data into unreadable formats using cryptographic algorithms, preventing unauthorized access and tampering. Encryption techniques typically fall into two categories:

• Symmetric Key Encryption: Same key for encryption and decryption.

• Public Key Encryption: Public key encrypts, private key decrypts—more secure for key sharing.

2. Key Technologies Used

• Chaotic Maps:
  Mathematical systems that exhibit unpredictable behavior, ideal for encryption. They generate complex key streams and enable secure pixel scrambling due to their sensitivity to initial conditions. Common chaotic systems include Logistic, Lorenz, and Rössler systems.

• DNA Encoding:
  Data is represented using DNA nucleotides (A, T, C, G). Binary values are mapped to DNA bases, allowing for high-density, stable, and compact data storage. DNA encoding introduces non-linearity and diffusion in encryption.

• Random Permutation:
  Random rearrangement of image pixels ensures unpredictability. Techniques like the Fisher-Yates shuffle help in uniformly permuting pixel positions, essential for robust encryption.

3. Hybrid Encryption Methodology

A proposed encryption approach combines chaotic maps (Lorenz system), DNA encoding, and Fisher-Yates shuffling. The process includes:

• Chaotic Key Generation:
  Based on the Lorenz system with user-specific keys derived from a SHA-256 password hash.

• Pixel Scrambling:
  Fisher-Yates shuffle using chaotic sequences to rearrange pixels.

• DNA Encoding & Modification:
  Each 8-bit pixel value is encoded into 4-base DNA sequences. Further modification is done using chaotic sequences.

• Chaotic XOR Diffusion:
  Final encrypted image is generated using an XOR operation with a chaotic sequence, ensuring complete diffusion of pixel changes.

Decryption follows the reverse steps using the same chaotic sequences and keys.

4. Security and Performance Analysis

• Histogram Analysis:
  Encrypted images exhibit uniform histograms, lacking patterns that attackers could exploit—indicating high security.

• Entropy Analysis:
  Encrypted images reach entropy values near 8, indicating excellent randomness and resistance to statistical attacks.

  Example: For the Baboon image, entropy increases from an average of 7.66 (plain) to 7.999 (encrypted).

• Correlation Analysis (not fully included in the provided text):
  Encryption significantly reduces the correlation between adjacent pixels, confirming high image randomness and security.

5. Related Research
Prior studies have validated the effectiveness of chaotic maps and DNA encoding:

• Low-dimensional chaotic systems (e.g., Logistic map) are simple but less secure.

• High-dimensional and hyperchaotic systems (e.g., Lorenz, Chen, Seven-Dimensional systems) offer better security due to complex behavior.

• DNA + Chaos hybrid models enhance encryption by adding multiple layers of confusion and diffusion.

Examples include:

• Baker Map + DNA operations

• 2D Sine-Logistic map + DNA rules

• Hyperchaotic Lorenz + DNA XOR operations

Conclusion

In this work, we propose a robust image encryption and decryption framework that integrates high-dimensional chaotic sequences, DNA encoding, and the Fisher-Yates shuffle to enhance security. The encryption process utilizes the Lorenz chaotic system to generate pseudo-random sequences, which drive pixel shuffling and DNA-based transformations. Multiple rounds of Fisher-Yates shuffling and chaotic diffusion further strengthen security by ensuring high resistance against statistical and differential attacks. The decryption process accurately reverses the encryption steps using the same chaotic sequences derived from the password, ensuring precise image reconstruction. DNA encoding introduces an additional layer of complexity, while XOR-based chaotic diffusion increases randomness in pixel values, further enhancing security. The proposed encryption scheme demonstrates strong security properties, including high key sensitivity, robustness making it resistant to brute-force attacks, and statistical attacks. This conclusion is supported by performance evaluations using key metrics such as entropy, correlation coefficient, chi-square test, histogram analysis, NPCR, and UACI analysis. In all these metrics, the proposed scheme achieved optimal values, outperforming many existing encryption methods.

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Copyright

Copyright © 2025 T Pavan Kumar, Odugu Srinivasa Rao, K Saraswathi. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.