The Advanced Encryption Standard (AES) has now become the most widely applied symmetric-key algorithm. AES was announced by NIST in 2001 after a 5-year standardization process in which fifteen competing designs were presented and evaluated before Rijndael was selected as the most suitable. AES is the first publicly accessible and open cryptographic algorithm widely available in open source form. It is a very secure cryptographic algorithm which is supposed to be viable for the next fifty years and has been approved by the NSA for top security operations. Block size is 128 bits. Key size may be 128, 196 or 256 bits. 128 bits is regarded as capable of bringing acceptable security.