Data Encryption Algorithm DES
The Data Encryption Standard (DES) of the Data Encryption Algorithm (DEA) is a standardized description, which comes from IBM's research work , and was officially adopted by the US government in 1997. It is probably the most widely used key system, especially in securing financial data. DES was originally developed to be embedded in hardware. Usually, automated teller machines (ATMs) use DES.
DES uses a 56-bit key with an additional 8 parity bits, resulting in a maximum block size of 64 bits. It is an iterative block cipher that uses a technique called Feistel, in which the encrypted block of text is split in half. Apply a loop function to one half using the subkey, and then XOR the output with the other half; the halves are then swapped, and the process continues without swapping in the final loop. DES uses 16 cycles.
The main form of attacking DES is called a brute force or exhaustive key search, which involves repeatedly trying various keys until one matches. If DES uses a 56-bit key, the number of possible keys is 2^56. As the capabilities of computer systems continue to develop, the security of DES will be much weaker than when it first appeared. However, it can still be considered adequate from a practical point of view of non-critical nature. However, DES is now only used for authentication of old systems, and the new encryption standard - Advanced Encryption Standard (AES) is more often chosen.
A common variation of DES is triple DES, a mechanism that uses a 168-bit key to encrypt material three times; it usually, but not always, provides extremely strong security. Triple DES is backwards compatible with DES if all three 56-bit subelements are the same.
IBM held a patent on DES for several years, but this expired in 1983 and is in the public domain, allowing royalty-free use under certain conditions.