What is DES/TDES?
DES (Data Encryption Standard) was originally introduced by NSA (National Security Agency) and IBM and has since become a Federal data encryption standard as defined in FIPS 46-3 (Federal Information Processing Standard). DES works on 64-bit data segments with a 64-bit key of which 8 bits provide parity, resulting in a 56-bit effective length. A variant on DES is TDES, in which the plain text is processed three times with two or three different DES secret keys. With two encryption keys used, the result is an encryption equivalent to using a 112-bit (128-bit) key. With three keys, the result is an encryption equivalent to using a 168-bit (192-bit) key. In practice with a 128-bit TDES, the plain text is encrypted with the first key, decrypted with the second key, and then encrypted again with the first key.
