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Document Type

Article

Keywords

Diffusion, Encryption, Decryption, PRNG, ChaCha20, Fisher–Yates Shuffling.

Abstract

Data security remains a critical concern, especially for lightweight and resource-constrained environments. Traditional lightweight designs, such as those relying on linear congruential generators (LCGs) are susceptible to predictability and vulnerability to statistical attacks. This paper proposes an enhanced diffusion-based encryption framework that replaces the LCG with the ChaCha20 stream cipher for pseudorandom sequence generation and introduces a key-dependent bit-shuffling mechanism to strengthen diffusion. The methodology integrates three key stages. First, pseudorandom keystream generation is performed via ChaCha20 with a 256-bit key and a 96-bit nonce derived from the encryption key. Second, modular arithmetic-based diffusion (addition/XOR) is applied between the plaintext and the keystream. Finally, Fisher-Yates bit-level shuffling is seeded by the ChaCha20 output, ensuring robust decorrelation. Experimental evaluation demonstrates that the proposed scheme achieves near-ideal Shannon entropy (7.998–7.999 bits/byte), a negligible plaintext-ciphertext correlation (≈0.0142), and passes 100% of the NIST statistical randomness tests. The avalanche effect consistently reaches 100%, confirming high sensitivity to key and plaintext changes. Comparative analysis shows that the enhanced method provides superior security to LCG-based schemes while maintaining computational efficiency comparable to that of lightweight ciphers (AES, SIMON). The results confirm that the integration of ChaCha20 and enhanced bit-level diffusion significantly improves robustness against predictability and correlation attacks.

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