Cryptanalyzing and Improving an Image Encryption Algorithm Based on Chaotic Dual Scrambling of Pixel Position and Bit

Area of Science:

• Cryptography
• Image Processing
• Computer Science

Background:

• A novel image encryption algorithm utilizing double scrambling (pixel position and bit level) was proposed.
• The original algorithm claimed resistance against chosen-plaintext attacks using chaotic sequences.

Purpose of the Study:

• To cryptanalyze the claimed security of the double image encryption algorithm.
• To demonstrate the vulnerability of the algorithm to chosen-plaintext attacks.
• To propose an improved, secure image encryption algorithm.

Main Methods:

• Analysis of the encryption algorithm's key stream generation.
• Implementation of a chosen-plaintext attack to identify equivalent keys.
• Theoretical analysis and experimental verification of the attack's feasibility.

Main Results:

• The original algorithm's equivalent keys (scrambling sequence T, bit-level scrambling sequence WT, and diffusion sequence S) were identified.
• The generation of WT and S was found to be independent of the plaintext, enabling key stream cracking.
• The chosen-plaintext attack successfully decoded the encrypted images.

Conclusions:

• The analyzed double image encryption algorithm is insecure against chosen-plaintext attacks due to predictable key stream generation.
• An improved algorithm was developed, demonstrating enhanced security and achieving the effect of a "one-time pad".
• The findings highlight the importance of rigorous cryptanalysis for chaotic image encryption systems.