BOUKHALET, Fouina2019-07-212019-07-212019http://dspace.univ-msila.dz:8080//xmlui/handle/123456789/15515In this memo, we study the congruences and application in cryptography. First, we study the concept and some properties of congruences without forgetting mention some special theorems: Wilson, Fermat and Euler. Also, we study some encryption methods in cryptography and the role of congruence in this type of encryption. We provided in the clasical gryptography the substitution ciphers (Shift Cipher, affine Cipher and Vigenère Cipher), and in the asymmetric encryption (RSA Cryptosystem, Diffie-Hellmun Key Exchange, The ElGamal Cryptosystem). Such that, the RSA method based on the difficulty of factorization the prime number, and the Elgamal method based on the difficulty of solving the problem of Diffie-HellmanenCongruences , application , cryptographyThesis