Asymmetric Cryptosystem Using Af fine Transform in Fourier Domain Savita Anjana, Indu Saini, Phool Singh and A. K. Yadav Abstract An improved image encryption scheme that uses af fine transform and asymmetric keys in Fourier transform domain has been proposed. The scheme is validated for grayscale images through numerical simulation using MATLAB 7.14. In the proposed scheme, the decryption keys are different from the encryption keys and are obtained by phase truncation Fourier transform method. The performance of the scheme is evaluated in terms of the metrics such as correlation coef ficient, mean-squared error, and peak signal-to-noise ratio. We have carried out the sen- sitivity analysis relative to the af fine transform parameter, which serves as an additional security feature. The robustness of the scheme is demonstrated by showing its resistance against noise and occlusion attacks. Since this is the first study that uses af fine transform in the phase-truncated Fourier transform based asymmetric cryptosystem, it provides a new scheme for image encryption with enhanced security. Keywords Af fine transform ⋅ Asymmetric cryptosystem ⋅ Fourier transform 1 Introduction In the recent years, there have been tremendous research activities going on in the field of information security due to fast adoption of digital technology. These efforts are aimed at improving the existing techniques as well as developing new schemes which are ef ficient and secure. During the past decade, various techniques [1] have been developed for secure communication and transmission of the data. The schemes are broadly classified as purely optical, purely digital, and hybrid tech- niques, each having its own advantages. Most of the recent optical image S. Anjana ⋅ I. Saini ⋅ P. Singh ( ✉ ) Department of Applied Sciences, The NorthCap University, Gurugram 122017, India e-mail: Phool.singh24@gmail.com A. K. Yadav Department of Applied Mathematics, Amity University Haryana, Gurugram 122413, India © Springer Nature Singapore Pte Ltd. 2018 S. Bhattacharyya et al. (eds.), Advanced Computational and Communication Paradigms, Advances in Intelligent Systems and Computing 706, https://doi.org/10.1007/978-981-10-8237-5_4 29