CoreDES

v4.0

7

Decryption

To begin the process of decrypting data, the following

inputs are set:

1. K[1:64] is set to the cipher key (ck1 in Figure 7) to

decrypt the data.

2. D[1:64] is set to the ciphertext data (d1 in Figure 7)

to be decrypted.

3. ED is set to logic '0'.

4. EN is set to logic '1'.

After 16 clock cycles of the EN input being held

continuously at a logic '1' value, the QVAL signal will

transition from logic '0' to logic '1' and remain valid for

one

clock

cycle,

indicating

that

valid

plaintext

(unencrypted data shown as q1 Figure 7) is available on

the Q[1:64] outputs.

Figure 7 • Example Decryption Sequence

CLK

K[1:64]

D[1:64]

ED

EN

1

2

3

4

5

6

7

8

9 10 11 12 13 14 15 16

cycle

Q[1:64]

QVAL

q1

ck1

d1

Don't care

Undefined