TM4C129CNCPDT Datasheet, PDF (998/1753 Pages) Texas Instruments – Tiva Microcontroller

Data Encryption Standard Accelerator (DES)
Figure 14-2. DES - ECB Feedback Mode
Input buffer
(plain text)
64
Data_in
Key register
Key in
192
DES core
(encrypt)
64 Data_out
Key register
Key in
192
Input buffer
(cipher text)
64
Data_in
DES core
(decrypt)
64 Data_out
Output buffer
(cipher text)
Output buffer
(plain text)
Encryption
Decryption
14.4.1.1
CBC Feedback Mode
Figure 14-3 on page 998 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
Input buffer
(plain text)
64
IV register
64
64
64
64
data_in
Key register
Key in
192
DES core
(encrypt)
64
data_out
IV register
Key register
Temporary
register
64
Key in
192
64
Input buffer
(cipher text)
64
data_in
AES core
(decrypt)
data_out
64
64
Output buffer
(cipher text)
Encryption
Output buffer
(plain text)
Decryption
14.4.1.2
CFB Feedback Mode
Figure 14-4 on page 999 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 via 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.
998
June 18, 2014
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