It is a symmetric-key block cipher designed by IBM and published by the National Institute of Standards and Technology (NIST). The plaintext is broken into blocks of 64-bits and encryption is performed block-wise. This means that the cryptographic key and the algorithm are applied to it together rather than one bit at a time. The encryption process consists of 16 rounds and each block is encrypted using a key to a cipher-text (64-bits) by using permutations and combinations. They key used in DES has 56-bits as a functional key while the rest 8 bits are for parity checking. DES was actually the first encryption algorithm approved by the US government for public disclosure. DES is insecure due to its small key size and the most common attack affecting DES is the brute force attack.
1. Brute Force attacks are common since the key length is mall for DES (64 bits).
2. Differential Cryptanalysis can break full 16-round DES by using 247 chosen plaintext.
3. A man-in-the-middle attack requires complexity of 232 to break 6-round DES.
4. Linear cryptanalysis can break DES using 243 known plaintext
5. A combination of linear and differential cryptanalysis called ‘differential-linear’ cryptanalysis can also break DES depending on how many rounds
6. Davies Attack (DA) can break DES with 250 known plaintext.