Known plain-text Attack on Asymmetric Cryptosystem

It is believed that asymmetric cryptosystem based on phase-truncated Fourier transform has immunity against known-plaintext attack. However, generation of two asymmetric keys is possible, if plaintext-ciphertext pair is known. In this paper, we show that amplitude- and phase-truncation-based asymmetric cryptosystem is vulnerable to known-plaintext attack. The decryption keys are generated with the help of modified Gerchberg-Saxton phase retrieval algorithm from known-plaintext and cipher-text. The first key is generated from known-plaintext and the second key is generated from the cipher-text. With the help of the generated keys, the encrypted image in one domain is decrypted successfully in another domain. The domains used for this study are Fourier, Fresnel, fractional Fourier or gyrator domain. The vulnerability is proved through the results of computer simulation.