International Journal of Computing and Digital Systems ISSN (2210-142X) Int. J. Com. Dig. Sys. 12, No.1 (Sep-2022) E-mail: dralhusainy@gmail.com, alsewadi@hotmail.com, bshargabi@meu.edu.jo http://journals.uob.edu.bh https://dx.doi.org/10.12785/ijcds/120168 Image Encryption using a Binary Search Tree Structure-Based Key Mohammed Abbas Fadhil Al-Husainy 1 , Hamza A. A. Al-Sewadi 2 and Bassam Al-Shargabi 3 1 Al-Maaqal University, Basrah, Iraq 2 Iraq University College, Basrah, Iraq 3 Middle East University, Amman-Jordan Received 21 Jun. 2021, Revised 29 Mar. 2022, Accepted 20 May 2022, Published 30 Sep. 2022 Abstract: Due to the ever-increasing cybercrime and hazards on digital information stored or in transit over computer clouds and networks, so many encryption algorithms were developed and practically implemented. On the other hand, hackers and intruders keep on developing methods to break those algorithms. Hence, new methods are always sought and developed by researchers. A binary search tree (BST) is implemented in this paper to produce a new algorithm for image encryption. The BST is utilized to generate an encryption key that consists of two parts; local and global with flexible length capabilities that provide better security. Sharing all image contents to encrypt any byte of the source image helped to achieve Shannon’s concept of diffusion and confusion. The experimental application of this algorithm has manifested a satisfactory security performance as compared with the widely used cryptographic systems such as Advanced Encryption Standard (AES) and Data Encryption Standard (DES). These Comparisons included measurement of encryption time complexity, Peak Signal to Noise Ratio (PSNR), Entropy, encryption key space. Besides, the new method offers encryption key length flexibility and involvement of all image contents in its generation. Keywords: Image-Encryption, Data-security, Cryptography, Avalanche-Effect, Binary Search Tree. 1. INTRODUCTION With the vast growth of computer systems involved in all walks of life for storage, processing and communication, the security, integrity, and authenticity became of prime concern. The solution to this problem can be achieved by either cryptography or data hiding algorithms. Efficient cryptographic algorithms such as advanced encryption standard (AES), data encryption standard (DES), triple DES, and many others [1]–[3] were developed and practically implemented for encrypting all sorts of multimedia (texts, images, audio, and video files). However, with the increased computer efficiency and capabilities, the worrying growth of data security breaching measures by hackers and criminals, demanded continuous efforts to develop new security algorithms. Therefore, great efforts are spent by industrial and academic research teams in order to protect commercial and governmental data that is either transmitted over various digital communication channels or is stored in computer systems [4]. Prior to 1976, only symmetric cryptographic algorithms were known, where only one secret key is needed to be used for both encryption and decryption (referred to as secret-key algorithms). These algorithms require a secure channel to distribute the secret key to intended users. However, a new technique, developed by Diffie and Hillman [5] suggested an asymmetric algorithm which solved the problem of key distribution. It uses a pair of different, but related keys; one is made public and the other is private. One is used for the encryption process while the other for decryption process (referred to as a public-key algorithm). Symmetric algorithms are comparatively fast and more difficult to break, but has the serious drawback of key distribution, while asymmetric algorithms are slower and less secure, but do not need key distribution, besides, it is suitable for key distribution [6][7].