Uncorrected Author Proof Journal of Intelligent & Fuzzy Systems xx (20xx) x–xx DOI:10.3233/JIFS-201146 IOS Press 1 Hash-enhanced elliptic curve bit-string generator for medical image encryption 1 2 Omar Reyad a,b,∗ , Kadry Hamed c,d and Mohamed Esmail Karar a,e 3 a College of Computing and Information Technology, Shaqra University, Saudi Arabia 4 b Faculty of Science, Sohag University, Egypt 5 c College of Sciences and Humanities, Shaqra University, Afif, Saudi Arabia 6 d Faculty of Computers and Information, Minia University, Egypt 7 e Faculty of Electronic Engineering, Menoufia University, Egypt 8 Abstract. Bit-string generator (BSG) is based on the hardness of known number theoretical problems, such as the discrete logarithm problem with the elliptic curve (ECDLP). Such type of generators will have good randomness and unpredictability properties as it is challenged to find a solution regarding this mathematical dilemma. Hash functions in turn play a remarkable role in many cryptographic tasks to accomplish different security levels. Hash-enhanced elliptic curve bit-string generator (HEECBSG) mechanism is proposed in this study based on the ECDLP and secure hash function. The cryptographic hash function is used to achieve integrity and security of the obtained bit-strings for highly sensitive plain data. The main contri- bution of the proposed HEECBSG is transforming the x-coordinate of the elliptic curve points using a hash function H to generate bit-strings of any desirable length. The obtained pseudo-random bits are tested by the NIST test suite to analyze and verify its statistical and randomness properties. The resulted bit-string is utilized here for encrypting various medical images of the vital organs, i.e. the brain, bone, fetuses, and lungs. Then, extensive evaluation metrics have been applied to analyze the successful performance of the cipherimage, including key-space analysis, histogram analysis, correlation analysis, entropy analysis and sensitivity analysis. The results demonstrated that our proposed HEECBSG mechanism is feasible for achieving security and privacy purposes of the medical image transmission over unsecure communication networks. 9 10 11 12 13 14 15 16 17 18 19 20 21 Keywords: Elliptic curve cryptography, hash function, bit-string generator, medical image encryption, security analysis 22 1. Introduction 23 A pseudo-random bit generator (PRBG) is an 24 algorithm for producing a string of random bits 25 to represent almost similar properties of bit-strings 26 produced from a truly random bit generator. The 27 obtained bit series from the PRBG is estimated by 28 a comparative set of known initial values, called the 29 PRBG’s seed [1]. Although PRBG strings are closed 30 to truly random sequences, they could be gener- 31 ated by using hardware random bit-string generators. 32 ∗ Corresponding author. Omar Reyad. E-mail: oreyad@ science.sohag.edu.eg. Therefore, PRBGs are implemented in real world 33 applications for speeding-up the generated bits, and 34 also for the reproducibility. PRBGs are widely used 35 in many recent applications such as electronic games, 36 numerical simulations, statistical research, random- 37 ized algorithms, cryptography, and lottery. 38 In 1985, elliptic curve cryptography (ECC) were 39 introduced by Neal Koblitz [2] and Victor Miller [3]. 40 By substituting the subgroup of the multiplicative 41 group Z ∗ p with the group of points on an elliptic curve 42 (EC) over a finite field F, these cryptosystems could 43 be considered as EC-analogues of the traditional 44 discrete logarithm ones. The security beyond these 45 EC-cryptosystems is proven by the computational 46 ISSN 1064-1246/20/$35.00 © 2020 – IOS Press and the authors. All rights reserved