Abstract- Cryptography is the mathematical system which is used to provides privacy and authentication to the data. Now a day’s Modern Cryptography is used everywhere for security of data, For example in Banking sector where thousands of transaction takes place every minute, Military where security and authentication of the data is very important, Social websites where lots of personal data of people must be secure etc. To understand the working of Modern cryptography we first need to understand the base of cryptography i.e. we need to understand Traditional cryptography. This paper gives the description of Modular arithmetic, Congruence, Modular multiplicative inverse, Shift cipher and its implementation in C++, Affine cipher its implement...