Key Register
Output Buffer
(plain text)
DES Core
(encrypt)
64
64
Key in
192
data_out
Input Buffer
(plain text)
IV Register
64
data_in
Temporary
Register
64
64
Key Register
Output Buffer
(plain text)
DES Core
(encrypt)
64
64
Key in
192
data_out
Input Buffer
(plain text)
IV Register
64
data_in
Temporary
Register
128
64
Encryption
Decryption
Key Register
Output Buffer
(cipher text)
AES Core
(encrypt)
64
Key in
192
data_out
Input Buffer
(plain text)
IV Register
64
64
64
data_in
Key Register
Output Buffer
(plain text)
AES Core
(encrypt)
64
64
Key in
192
data_out
Input Buffer
(plain text)
IV Register
64
64
64
data_in
Temporary
Register
64
64
DES Supported Modes of Operation
857
SLAU723A – October 2017 – Revised October 2018
Copyright © 2017–2018, Texas Instruments Incorporated
Data Encryption Standard Accelerator (DES)
14.5.1.1 CBC Feedback Mode
shows the CBC feedback mode of operation, where the input data is XORed with the
initialization vector (IV) before it is passed to the basic crypto core. The output of the crypto core is passed
directly to the output buffer. For decryption the operation is reversed, resulting in an XOR at the output of
the crypto core.
Figure 14-3. DES3DES – CBC Feedback Mode
14.5.1.2 CFB Feedback Mode
shows the CFB mode of operation for encryption and decryption. The input for the crypto core
is the IV; the result is XORed with the data. The result is fed back using the IV register, as the next input
for the crypto core. The decrypt operation is reversed, but the crypto core is still performing an encryption.
Figure 14-4. DES3DES – CFB Feedback Mode