A novel 1-D compound sine-cosine chaotic map & novel pseudorandom key based biometric image encryption method

In today’s world, protecting biometric data is more important than ever, as it plays a key role in verifying identities. Sectors like banking, mobile commerce, military, and immigration rely on biometric images for authentication, making them targets for malicious attacks during transmission and storage. It is essential to preserve the privacy, accuracy and reliability of these images. Traditional encryption methods often struggle with the complex structure and large size of biometric images. Chaos-based cryptosystem provides an effective solution owing to its ergodicity and unpredictability. Chaos-based PRNGs have emerged as a powerful solution for encryption, relying on the complex and random nature of chaotic maps. This paper presents a new biometric image encryption scheme that uses novel One-dimensional Compound Sine-Cosine(1DCSC) chaotic map and novel pseudorandom key. The proposed work is divided into three tasks. Firstly, a bit permutation process is applied to generate intermediate keys, which are further processed using XOR operations along with circular left and right bit rotations to produce pseudorandom keys for the red, green, and blue color components. Secondly, a novel 1DCSC chaotic function which combines sine and cosine dynamics, is employed to generate a highly sensitive pseudorandom chaotic sequence. Finally, both chaotic sequence and novel pseudorandom keys are used to encrypt red, green and blue components of the given colour image. The proposed 1DCSC chaotic map has been assessed through bifurcation diagrams, Shannon entropy, Lyapunov exponent, NIST tests, and the 0–1 test, yielding a strong Lyapunov exponent value of 5.47 and a chaotic range spanning from 19 to 350. Security analysis, including Correlation Coefficient (CC), NPCR, UACI and entropy tests also demonstrates that the proposed scheme effectively resists known attacks, achieving a high entropy value of 7.9997.