Data Encryption Standard
The Data Encryption Standard (DES) represents a secret key encryption scheme, which was officially selected as the Federal Information Processing Standard for the USA by the National Bureau of Standards (today National Institute of Standards and Technology - NIST) in 1976 (Davies & Price, 1989). Later it was distributed on the international level and enjoyed by a great number of people. It is based on 56-bit key, which today is regarded as not sufficient due to the fact that it can be rather easily cracked with the use of brute force (Schneier, 2004). There is also evidence that the cipher has certain theoretical weaknesses. The Triple DES form of the algorithm is believed to be much more secure, but recently the Advanced Encryption Standard superseded DES, which is why it was withdrawn as a standard by NIST.
DES was developed by the IBM Company in response to the NIST’s request of developing a government-wide standard for encrypting sensitive and unclassified information (Thomas, 2009). The US National Security Agency made several changes in DES later. The original standard was based on a key that used 64-bit secret key and it is believed that removal of the 8 bits was made so as the US government agencies could crack messages in secret (Kumar et al., 2006).
According to the algorithm, encryption of the message block has 16 stages, which are also called rounds. The process is systematically depicted in Figure 1. Sixteen 48-bit keys are generated from the input key. One of them is used in each round, as well as eight S-boxes (Kinnucan, 1978). The latter ones are fixed in the standard specification. With the use of S-boxes groups of 6 bits are mapped to the ones of four bits. The U.S. National Security Agency determined the contents of these boxes. They are randomly filled and recently it was discovered that they are resistant against differential cryptanalysis attack, which was first known in the 1990s.
Figure 1. Scheme of DES work (DES Encryption Algorithm, 2005).
Davies, D.W. & Price, W. L. (1989). Security for computer networks, 2nd ed. New York: John Wiley & Sons.
Kinnucan P. (1978). Data Encryption Gurus: Tuchman and Meyer. Cryptologia 2(4), 371.
Kumar S., Paar C., Pelzl J., Pfeiffer G., Rupp A., Schimmler M. (2006). How to Break DES for Euro 8,980. 2nd Workshop on Special-purpose Hardware for Attacking Cryptographic Systems — SHARCS 2006, Cologne, Germany.
Schneier, B. (2004). Perspective: Saluting the data encryption legacy. Retrieved from http://news.cnet.com/Saluting-the-data-encryption-legacy/2010-1029_3-5381232.html
The DES Encryption Algorithm. (2005). Retrieved from http://www.iusmentis.com/technology/encryption/des/
Thomas, R. J. (2009). American Cryptology during the Cold War, 1945-1989. Book III: Retrenchment and Reform, 1972-1980. United States Cryptologic History 5(3), 232.