CoreDES

The CoreDES macro implements the Data Encryption Standard (DES), which provides a means of securing data. The DES algorithm is described in Federal Information Processing Standards (FIPS) Publication (PUB) 46-3. The algorithm CoreDES takes as input 64 bits of plaintext data and 64 bits of a cipher key (only 56 of the 64 bits of the key are used in the calculations, as the least significant bit of each byte of the cipher key is used to provide odd-parity for the key bytes) and after 16 cycles, produces a 64-bit ciphered version of the original plaintext data as output. During the 16 cycles or iterations of the algorithm, the data bits are subjected to permutation and addition functions, which consist of key schedules, calculated by rotations and permutations applied to the original 56-bit cipher key. Figure 1 illustrates the 16-iteration DES algorithm, as described in detail in FIPS PUB 46-3.