In order to improve the security and efficiency of image encryption systems comprehensively, a novel chaotic S-box based image encryption scheme is proposed. Firstly, a new compound chaotic system, Sine-Tent map, is proposed to widen the chaotic range and improve the chaotic performance of 1D discrete chaotic maps. As a result, the new compound chaotic system is more suitable for cryptosystem. Secondly, an efficient and simple method for generating S-boxes is proposed, which can greatly improve the efficiency of S-box production. Thirdly, a novel double S-box based image encryption algorithm is proposed. By introducing equivalent key sequences {r, t} related with image ciphertext, the proposed cryptosystem can resist the four classical types of attacks, which is an advantage over other S-box based encryption schemes. Furthermore, it enhanced the resistance of the system to differential analysis attack by two rounds of forward and backward confusion-diffusion operation with double S-boxes. The simulation results and security analysis verify the effectiveness of the proposed scheme. The new scheme has obvious efficiency advantages, which means that it has better application potential in real-time image encryption.Entropy 2019, 21, 790 2 of 20 (or shuffling, scrambling) process plays a role in confusing the relationship between the cipher image and plain image. The function of the diffusion process is to spread the change of one pixel value in the plain image to the whole range of the cipher image. Based on the basic confusion-diffusion architecture, researchers have proposed many novel concrete encryption strategies. In Ref. [18][19][20][21][22][23][24], authors proposed some different permutation strategies for image scrambling aiming at the confusion process. In Ref. [22,[25][26][27][28][29], authors put forward some novel image diffusion algorithm. In Ref. [30][31][32][33][34][35][36], authors adopt new chaotic systems to improve the complexity and randomness of chaotic key streams. Some other cryptographic methods have also been tried by many researchers. For example, some cryptographic algorithms are based on bit-level permutation and diffusion [30], and some algorithms introduce the DNA coding mechanism [37], and some algorithms mainly use S-box to encrypt images [38][39][40]. However, some image encryption schemes exist as obvious security vulnerabilities. Thus, these image encryption schemes cannot resist some attacks, such as the chosen/known plaintext. In addition, some image encryption algorithms are inefficient, such as using bit-level image scrambling, DNA encoding mechanism, key related to plaintext Hash value [41,42], and the high-dimensional chaotic system [43,44]. Encryption algorithms with low efficiency are not suitable for some resource-constrained environments, such as mobile social network [45], sensor network communication environment [46] and searchable encryption [47]. Compared with high-dimensional continuous-time chaotic systems, low-dimensional discrete chaotic systems can generate chaot...

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In this paper, a new one-dimensional fractional chaotic map is proposed and an image encryption scheme based on parallel DNA coding is designed by using the chaotic map. The mathematical model of the new chaotic system combines a sine map and a fraction operation. Compared with some traditional one-dimensional chaotic systems, the new chaotic system has a larger range of chaotic parameters and better chaotic characteristics, which makes it more suitable for applications in information encryption. In addition, an image encryption algorithm based on parallel DNA coding is proposed, which overcomes the shortcoming of common DNA coding-based image encryption algorithms. Parallel computing significantly increases the speed of encryption and decryption algorithms. The initial key of the cryptosystem is designed to be related to the SHA-3 hash value of the plaintext image so that the algorithm can resist a chosen-plaintext attack. Simulation experiments and security analysis results show that the proposed image encryption scheme has good encryption performance and less time overhead, and has strong robustness to noise and data loss attacks, which indicates that the proposed image encryption scheme has good application potential in secure communication applications.