DSP Applications and Student Projects - Digital Signal Processing and Applications with the C6713 and C6416 DSK - page 428

TABLE 10.13 P -Box

67 0 1 9 2 8 7 1 5 3 6 5 8 1 0
28 4 4 2 7 3 9 9 3 0 6 2 1 4 5

L i- 1 R i- 1

32

Expansion
E(R i- 1 )

48

48

K i

48

6 6

S1 S8

4 4

32

Permutation P

32

32

32

R i

FIGURE 10.58. Core f -function of DES.

permutation occurs, which reverses the initial permutation, yielding an encrypted
data signal.
The signal output from the encryption algorithm is not decipherable by the
human ear even if the signal is filtered in any way. For testing purposes, the first
three onboard switches were utilized: sw 0 for selecting different keys; sw 1 to enable
encryption only, or both encryption and decryption; and sw 2 as an on/off switch (a
loop program).