AES is one of the most widely used block ciphers in modern applications. The Rijndael algorithm was selected as the AES after a 5-year public competition to choose a replacement for DES. It has a fixed block size of 128 bits and varying key sizes of 128, 192, or 256 bits. AES is an iterated cipher: the number of rounds of iteration depends on the key length.
AES is secure against all known attacks. There appear to be no ways to attack AES that are faster than exhaustive search. The best ways to attack AES only apply to variants of the cipher that have the fewest iterations.
