Cryptography is referred as "The study of secret". Encryption process is basically used for converting normal text into unreadable form. Security is one of the most challenging aspects in the internet and networks. Cryptography is the one of the main categories that converts information into an unreadable form. Cryptography allows people to carry their confidential data over the network without worries and insecurity. This paper provide comparison between three symmetric key cryptosystem i.e. DES, AES and triple DES.