Understanding DES (Encryption Method)

The Data Encryption Standard (DES) is a cipher block using keys of 56 bits. It's job today is no longer recommended because of its slowness in implementation and its key space is too small for a systematic attack in a reasonable time. It is used generally in Triple DES, which does nothing to improve its performance. DES has been used in the system of passwords for UNIX operating system.

The first standard was published by FIPS in January 15 1977 under the name FIPS PUB 46.

History

In May 1973, the National Bureau of Standards (U.S.) calls for the creation of an encryption algorithm used by businesses. At that time, IBM already had an algorithm called Lucifer, designed in 1971 by Horst Feistel.

Ideally, this algorithm should have been selected by the NBS. In practice, this was almost the case. Thus DES was created, which was adopted as the standard in November 1976.

This prompted rumors that the NSA had deliberately weakened the algorithm in order to break it. Strangely, the DES has proved resistant to several attacks not to appear in the academic community until much later.

Operation

The DES algorithm transforms a block of 64 bits into another block of 64 bits. It handles individual keys of 56 bits, represented by 64 bits (with a bit of each byte used for parity check). The symmetric encryption system is part of the family Encryption iterative block.

Broadly speaking, we can say that it works in three stages:

* Initial permutation and sets a block (with no impact on the security level).

* The result is subject to 16 iterations of a transformation; these iterations depend on each round and another key of 48 bits. The key intermediate round is calculated from the initial key of the user (through a network of alternative tables and operators XOR). At each round, the 64-bit block is divided into two blocks of 32 bits, and these blocks are exchanged with one another under a scheme of Feistel. The block of 32 bits with the highest weight (which extends from bit 32 bit 63) will undergo a transformation.

* The final outcome of the last round is transformed by the inverse function of the initial permutation.

DES uses eight tables substitution (S-Boxes) that was the subject of much controversy as to their content. Suspected weakness inserted by the designers. These rumors were dispelled in the early 90s by the discovery of differential cryptanalysis that showed the tables were well designed. Thus, DES is a sound encryption method which may be used with encryption software such as TrueCrypt.