Triple DES

The progress on exhaustive key searches against DES in the 1990s began to cause disquiet among mainstream users of DES, such as those in the financial sector, especially since it takes an enormous amount of time and money to change encryption algorithms that are widely adopted and embedded in large security architectures.

The pragmatic response was not to abandon the use of DES completely but to change how DES is used. That resulted in Triple DES (sometimes known as 3DES). Confusingly, there are two variants of Triple DES known as 3-key Triple DES $(_{3}TDES)$ and 2-key Triple DES $(_{2}TDES)$. We’ll describe these separately.

3-Key Triple DES

The variant of Triple DES known as $_{3}TDES$ is depicted in the illustration below.