Core3DES
The Triple DES encryption algorithm is executed in the
specific sequential order shown in Figure 2.
2. Decrypt using DES with cipher key K2 (middle
third of 168-bit cipher key).
1. Encrypt using DES with cipher key K1 (left third of
168-bit cipher key).
3. Encrypt using DES with cipher key K3 (right third
of 168-bit cipher key).
K1
K2
K3
DES
(Encrypt)
DES
(Decrypt)
DES
Plaintext Data
Ciphertext Data
(Encrypt)
Figure 2 • Triple DES Encryption Flow Diagram
The Triple DES decryption algorithm is executed in the
specific sequential order shown in Figure 3.
2. Encrypt using DES with cipher key K2 (middle third
of 168-bit cipher key).
1. Decrypt using DES with cipher key K3 (right third
of 168-bit cipher key).
3. Decrypt using DES with cipher key K1 (left third of
168-bit cipher key).
K3
K2
K1
DES
(Decrypt)
DES
(Encrypt)
DES
Ciphertext Data
Plaintext Data
(Decrypt)
Figure 3 • Triple DES Decryption Flow Diagram
Since three sequential DES operations are required, the
total compute time for Triple DES (encryption or
decryption) is three times that for single DES or 16 x 3 =
48 clock cycles.
2. Iteration state machine logic – keeps track of
which round of the Triple DES algorithm is
currently in progress.
3. Key schedule logic – computes the intermediate
keys at each round of the Triple DES algorithm.
Core3DES consists of four main blocks (Figure 4).
1. Data schedule logic – computes the intermediate
data values at each round of the Triple DES
algorithm.
4. Parity check logic
–
checks for odd-parity
compliance of the 168 bits of cipher key and issues
an error signal if parity is not correct.
Data
schedule
logic
Data In
Data Out
Iteration
state
machine
Key
schedule
logic
Cipher Key
Select Lines
Cipher Key
(K1,K2,K3)
Parity
check
logic
Parity Error
Parity Enable
Figure 4 • Core3DES Block Diagram
v5.0
3
ACTEL [ Actel Corporation ]
