CoreDES

2

v4.0

General Description

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 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.

Contents

General Description .................................................... 2

CoreDES Device Requirements .................................. 4

CoreDES Verification .................................................. 4

I/O Signal Descriptions ............................................... 5

CoreDES Operation .................................................... 5

Encryption ................................................................... 6

Decryption .................................................................. 7

Pause/Resume ............................................................. 8

Clear/Abort ................................................................. 9

Modes of Operation ................................................... 9

Ordering Information .............................................. 10

Export Restrictions .................................................... 10

List of Changes ......................................................... 11

Datasheet Categories ............................................... 11

Figure 1 • DES Algorithm

Left and Right

Data Halves after

Initial Permutation

Left and Right

Data Halves after

Round 1

Left and Right

Data Halves

after Round 2

Left and Right

Data Halves

after Round 16

Key Schedule 1

Key Schedule 2

L0

R0

+

R1 = L0

f(R0,K1)

f

L1 = R0

+f

K1

K2

R2 = L1

f(R1,K2)

L2 = R1

L16 = R15

R16 = L15

f(R15,K16)

Input

Initial

Permutation

Inverse Initial

Permutation

Output

16 Rounds

of Computation

Key