Encryption is one of the most frequently used tools in data communications to prevent unwanted access to the data. In the field of image encryption, chaos-based encryption methods have become very popular in the recent years. Chaos-based methods provide a good security mechanism in image communication. In this chapter, chaotic skew-tent map is adapted to encode an image. Seventy-two bit external key is considered (besides the initial parameters of the chaotic system) initially, and after some processing operations, 64 bit internal key is obtained. Using this key, every pixel is processed. The internal key is transformed using some basic operations to enhance the security. The decryption method is very simple so that authentic users can retrieve the information very fast. Every pixel is encrypted using some basic mathematical operations. The values of various test parameters show the power and efficiency of the proposed algorithm, which can be used as a safeguard for sensitive image data and a secure method of image transmission.
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At present, digital images are used as a frequent medium to transfer messages. Therefore it is very important to secure the digital images. Many real life applications demand reliable, fast and secured encryption of images. Some examples of the real life scenarios where the security of the images are vital are: army image databases, video conferencing, various medical images and their automated analysis results (Chakraborty, Chatterjee, Dey, Ashour, & Shi, 2018; Chakraborty, Mali, Chatterjee, Banerjee, Roy, Deb, et al., 2018;. Chakraborty, Mali, Chatterjee, Banerjee, Roy, Dutta, et al., 2018; Shouvik Chakraborty, Chatterjee, Dey, et al., 2017; Chakraborty et al., 2019; S. Hore et al., 2016; Hore et al., 2015; M. Roy et al., 2017; Roy et al., 2017), online personal photographs, images in social networking sites etc. This requirement is the main inspiration of image encryption systems. In the last decade, a good number of encryption algorithms (Ahmad, Alam, Umayya, Khan, & Ahmad, 2018; Bourbakis & Alexopoulos, 1992; Chakraborty, Seal, Roy, & Mali, 2016; Chang, Hwang, & Chen, 2001; H. K. C. Chang & Liu, 1997; Chen, Mao, & Chui, 2004; Cheng, 2000; Fridrich, 1998; Jui-Cheng & Jiun-In Guo, n.d.; Li & Zheng, 2002; Li, Zheng, Mou, & Cai, n.d.; Liu & Xia, 2017; Mali, Chakraborty, Seal, & Roy, 2015; Refregier & Javidi, 1995; Scharinger, 1998; Seal, Chakraborty, & Mali, 2017; Yen, J.-C. Guo, 2000; Yen & Guo, 1999; Zhang & Chen, 2008) are proposed by many scientists based on various principles. Among these algorithms, chaos based encryption methods are well known for their security, complexity, speed etc. The digital images are not similar in nature like a text data. They possess some certain properties like: redundant data, high correlation value, less sensitive i.e. a small modification in the value of any pixel of the digital image does not heavily reduce the details and quality of the image. Some of the features of the image may not be always directly visible (Chakraborty, Chatterjee, Ashour, Mali, & Dey, 2017; Chakraborty, Chatterjee, Das, & Mali, 2020; Chakraborty & Mali, 2018; Chakraborty, Mali, Chatterjee, Banerjee, Sah, et al., 2017; Chakraborty, Roy, & Hore, 2016; Hore, Chatterjee, Chakraborty, & Shaw, 2016). The popular text encryption methods like DES, AES, IDEA are not suitable for digital images because of their high computational time and computational power (Seal, Chakraborty, & Mali, 2017). Digital image encryption systems should not take very high time for real life applications (Seal et al., 2017). If an encryption process with high degree of security takes too much time then, that method cannot be used in practical situations.