Color image encryption based on chaotic systems and elliptic curve ElGamal scheme

Color image can provide more information than gray image, so it is used more widely in the field of the communication. In recent years, how to safely encrypt images has received increasing attention. Numerous previous image encryption algorithms are based on the symmetric encryption algorithm, but each pair of users communicating with symmetric encryption algorithm can only use the key that others do not know, so when the sender communicates with a receiver multiple times or sends the message to multiple receivers, the key number will grow at a geometric rate, and key management will become a burden on the users. In this paper, we propose an asymmetric image encryption algorithm for the advantages that the key groups and the number of keys in secret information transmission among multiple people are very small, and key transmission mode is relatively simple and secure. In our algorithm, first, the plain image is compressed and then the color image is encrypted by using the improved 4D cat map followed by asymmetric encryption which is based on elliptic curve ElGamal encryption, and finally, the encrypted image is globally diffused. The performance analysis is performed on key spaces, key sensitivity, the capability of resisting statistical attacks, differential attacks, known plaintext attacks and chosen plaintext/ciphertext attacks and quality evaluation metrics of decrypted image. Simulation results show that the proposed algorithm has better security comparing with other algorithms.