DES stands for Data Encryption Standard, which is a famous symmetric-key algorithm previously used in many different applications and is defined in the Federal Information Processing Standards (FIPS) 46-3 document. DES is now considered to be insecure for many applications. This is mainly due to the 56-bit key size being too small. DES ‘Block Size’ which is 64 bits, corresponds to the number of bits in an input or output block of the block cipher.