AES Functional Description
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SWRU543–January 2019
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Advance Encryption Standard Accelerator (AES)
CTR and ICM Feedback Modes
Figure 17-4 shows the counter feedback (CTR/ICM) mode of operation. This operation encrypts the IV.
The output of the cryptographic core (encrypted IV) is XORed with the data, thus creating the output
result.
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 17-4. 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.
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