Encryption is the process of transforming plaintext into the ciphertext where plaintext is the input to the encryption process and ciphertext is the output of the encryption process. Decryption is the process of transforming ciphertext into the plaintext where ciphertext is the input to the decryption process and plaintext is the output of the decryption process. In this book 2 symmetric encryption algorithm (DES, RC4) and 1 asymmetric encryption algorithm (RSA) are implemented and their execution times are calculated according to the size of plaintext or text to be encoded. This algorithm is used to encrypt data by using ASCII values of the data to be encrypted. The secret key will be used to modify another string and that string is used as a key to encrypt or decrypt the data. So, it can be said that it is a kind of symmetric encryprion algorithm because it uses same key for encryption and decryption but by slightly modifying it. This algorithm operates when the length of input and the length of key are same.