The Data Encryption Standard (DES) was invented by the IBM Corporation in the 1970’s. During the process of becoming a standard algorithm, it was modified according to recommendations from the National Security Agency (NSA). The algorithm has been studied by cryptographers for over 30 years. During this time, no methods have been published that describe a way to break the algorithm, except for brute-force techniques. DES has a 56- bit key, which offers 256 or 7 x 1016 possible variations. There are a very small numbers of weak keys, but it is easy to test for these keys and they are easy to avoid.
Triple-DES is a method of using DES to provide additional security. Triple-DES can be done with two or with three keys. Since the algorithm performs an encrypt-decrypt-encrypt sequence, this is sometimes called the EDE mode. This diagram shows Triple-DES three-key mode used for encryption.
