



Digital Encryption Standard (DES)
Digital Encryption Standard (DES) is a symmetric block cipher with 64bit block size that uses using a 56bit key.
In 1977 the Data Encryption Standard (DES), a symmetric algorithm, was adopted in the United States as a federal standard.


Digital Encryption Standard encrypts and decrypts data in 64bit blocks, using a 56bit key. It takes a 64bit block of plaintext as input and outputs a 64bit block of ciphertext. Since it always operates on blocks of equal size and it uses both permutations and substitutions in the algorithm. DES has 16 rounds, meaning the main algorithm is repeated 16 times to produce the ciphertext. It has been found that the number of rounds is exponentially proportional to the amount of time required to find a key using a bruteforce attack. So as the number of rounds increases, the security of the algorithm increases exponentially.

For many years, DESenciphered data were safe because few organizations possessed the computing power to crack it. But in July 1998 a team of cryptographers cracked a DESenciphered message in 3 days, and in 1999 a network of 10,000 desktop PCs cracked a DESenciphered message in less than a day. DES was clearly no longer invulnerable and since then Triple DES (3DES) has emerged as a stronger method.
Triple DES encrypts data three times and uses a different key for at least one of the three passes giving it a cumulative key size of 112168 bits. That should produce an expected strength of something like 112 bits, which is more than enough to defeat brute force attacks. Triple DES is much stronger than (single) DES, however, it is rather slow compared to some new block ciphers. However, cryptographers have determined that triple DES is unsatisfactory as a longterm solution, and in 1997, the National Institute of Standards and Technology (NIST) solicited proposals for a cipher to replace DES entirely, the Advanced Encryption Standard (AES).


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