The Triple DES algorithm has to be implemented in several operational modes which are defined in the different standards. There is a special National Institute of Standards and Technology (NIST) publication named ‘SP800-38’ which defines in particular the four most commonly used modes. The four modes are: Electronic Code Book, or ECB; Cipher Block Chaining, or CBC; Output FeedBack, or OFB; and Cipher FeedBack, or CFB.