The word Cryptography in Greek means "Secret Writing". Cryptography is the technique which can convert the plain text to cipher text through encryption algorithm and convert cipher text to plain text through decryption algorithm. Cryptography is basically two types i.e. Symmetric Cryptography and Asymmetric Cryptography. Symmetric Cryptography is the first types of Cryptography. In Symmetric Cryptography sender and receiver use same key to encrypt and decrypt the data. AES and DES technique are implemented using symmetric key cryptography. In Asymmetric Cryptography sender and receiver use different key to encrypt and decrypt the data. RSA is most popular and widely used asymmetric key algorithm.