Key Register
IV Register
Input Buffer
(plain text)
Ouput Buffer
(cipher text)
AES Core
(encrypt)
128
256
128
128
Encryption
Temporary Buffer
128
Key In
128
data_in
data_out
128
Key Register
IV Register
Input Buffer
(cipher text)
Ouput Buffer
(plain text)
AES Core
(encrypt)
256
128
128
Decryption
Temporary Buffer
128
Key In
128
data_in
data_out
128
128
Key Register
Ouput Buffer
(cipher or plain text)
AES Core
(encrypt)
128
128
Key in
data_in
256
Encryption or Decryption
Temporary Buffer
128
Input Buffer
(plain or cipher text)
IV Register
IV Register (counter)
128-32n
32n
+
data_in
data_out
128
1
0
32n
127
128
AES Functional Description
665
SLAU723A – October 2017 – Revised October 2018
Copyright © 2017–2018, Texas Instruments Incorporated
Advance Encryption Standard Accelerator (AES)
The IV is built out of two components: a fixed part and a counter part. The counter part is incremented
with each block. The counter width is selectable per context and can be 16, 32, 64, 96, or 128 bits wide. In
this mode, encryption and decryption use the same operation.
Figure 9-4. AES Encryption With CTR/ICM Mode
NOTE:
The value for n can be 1, 2, 3, or 4 for CTR mode and is ½ for ICM mode.
9.2.3.1.4 CFB Mode
shows the full block (128 bits) CFB mode of operation for encryption and decryption. The input
for the cryptographic core is the IV; the result is XORed with the data. The result is fed back through the
IV register as the next input for the cryptographic core. The decryption operation is reversed, but the
cryptographic core still performs encryption.
Figure 9-5. AES – CFB Feedback Mode