IOSR Journal of Computer Engineering (IOSR-JCE) e-ISSN: 2278-0661,p-ISSN: 2278-8727, Volume 18, Issue 3, Ver. I (May-Jun. 2016), PP 48-52 www.iosrjournals.org DOI: 10.9790/0661-1803014852 www.iosrjournals.org 48 | Page Uses of Genetic Algorithm in Cryptanalysis of RSA Siham Zoubir 1 , Abderrahim Tragha 2 1 (Department of Modeling and information technology (TIM) / University Hassan II Mohammedia, Faculty of sciences Ben M’sik, Casablanca) Abstract : The information system security is nowadays paramount, it is for what we are focused in our research to talk about a basic of security which is cryptography, and specially about RSA algorithm, a system of coding with public key developed by Rivest, Shamir and Adleman (R.S.A in 1978).We will discuss tree points in our project, the first step is to understand operation of RSA; (preparation of the key, encryption text and decryption text), and we search how we can calculate a products of two binary numbers with a big size (p × q), and which will be the result? After that we will study the function of genetic algorithm and how we can use it to generate a new number of population that we can use them in our cryptanalysis of RSA algorithm. Keywords :Cryptography; Genetic algorithm (GA); Rivest Shamir and Adleman (RSA), algorithm of KARATSUBA I. Introduction Genetic algorithms, initiated in 1970s by John Holland, based on derivatives of the genetic and evolutionary mechanisms of nature techniques: cross, mutation, selection. Their fields of application are extensive. Besides the economy, they are used for optimization functions (De Jong (1980)), finance (Pereira (2000)), and in cryptography in 1993 by Spillman, Janssen, Nelson and Kepner and their job was to break a simple substitution. Several studies has been made in this topic; genetic algorithm approach was used only to break classical crypto systems (Mono-alphabetical Substitution, Poly alphabetical Substitution, Permutation cipher, transposition cipher, encryption of Merkle-Hellman, encryption of Chor-Rivest, encryption of Vernam). Cryptography is a huge topic, this paper will focus primarily on the crypto system RSA, and how we can use genetic algorithm in cryptanalysis of RSA. II. Crypto System RSA Initiated by Rivest, Shamir, Adleman in 1977, it’s the more uses algorithm in the word. And its security based on the factoring problem [3]. All the operation of crypto system RSA occurs in a set of integer. Are p and q two prime numbers with big size. We notes N = pq. The number N east calls RSA module. Let us suppose that two people A and B want to communicate in a secure way by using crypto system RSA. For that, they must, each one of them to prepare a RSA module, two keys e and d, to carry out a procedure of encrypting and signature anda procedure of decrypting and verification of the signature.  Example of factoring 77 = 7 x 11. 1562900109403 =?? If N = pq, how can we find p and q or calculating • (p -1)(q - 1). • Difficult problem if p and q are big In the first part of this work, we study the operation of encryption and decryption RSA. 1. Operation of RSA The different Operation of the RSA passes by the following stages [5]: 1.1. Preparation of the keys If Bruno wants to send a message to Alice So Alice carries out: Choice of p and q two prime numbers Calculation of n= p × q Calculation of φ (n) = (p-1) (q-1) Choice of an exhibitor and calculation of his reverse exhibitor e such as pgcd (e, φ (n))=1