SWRU543B January 2019 – June 2025 CC3230S , CC3230SF , CC3235MODS , CC3235MODSF , CC3235S , CC3235SF
ECB Feedback Mode
Figure 1-1 shows the basic ECB feedback mode of operation, where the input data is passed directly to the basic cryptographic core and the output is passed directly to the output buffer.
For decryption, the cryptographic core operates in reverse: the decryption data path is used for data processing, whereas encryption uses the encryption data path.
Figure 17-2 AES - ECB Feedback ModeCBC Feedback Mode
Figure 17-3 shows the CBC feedback mode of operation, where the input data is XORed with the IV before it is passed to the basic cryptographic core. The output of the cryptographic core passes directly to the output buffer and becomes the next IV.
The operation is reversed for decryption, resulting in an XOR at the output of the cryptographic core. The input cipher text of the current operation is the IV for the next operation.
Figure 17-3 AES - CBC Feedback ModeCTR 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 ModeThe value for n can be 1, 2, 3, or 4 for CTR mode and is ½ for ICM mode.
CFB Mode
Figure 17-5 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 17-5 AES - CFB Feedback ModeF8 Mode
Figure 17-6 shows the F8 feedback mode of operation for encryption and decryption. The input to the cryptographic core is the result of the XOR operation of the previous cryptographic core output, a constant IV, and a block counter. The output of the cryptographic core is XORed with the input to create the result. In this mode, encryption and decryption use the same operations.
Figure 17-6 AES - F8 ModeXTS Operation
Figure 17-7 shows the XTS mode of operation for encryption and decryption. The input to the cryptographic core is XORed with the IV; the output of the cryptographic core is XORed with the same IV. For decryption, the cryptographic core operates in reverse, but the XOR operations are the same.
Figure 17-7 AES - XTS OperationThe IV is created with an initial encryption, followed by an LFSR operation for each new block.
F9 Operation
Figure 17-8 shows the F9 authentication mode of operation, where the input to the cryptographic core is XORed with the IV, and the output is XORed with the previous result to create the next result. The cryptographic core output is fed back as IV for the next block. The result is the output of the last XOR operation of the cryptographic core output.
Figure 17-8 AES - F9 OperationCBC-MAC Operation
Figure 17-9 shows the CBC-MAC authentication mode of operation, where the input to the cryptographic core is XORed with the IV. The cryptographic core output is then fed back as IV for the next block. The last data input block is XORed with an additional input value stored in the temporary buffer; this can be any precalculated value and is dependent on the alignment of the last input block. The result is the cryptographic core output of the last encryption operation.
Figure 17-9 AES - CBC-MAC Authentication ModeGCM Operation
Figure 17-10 shows one round of a GCM operation for encryption and decryption. A 32-bit counter is used as IV (as it is for CTR mode). The data is encrypted in the same way as in CTR mode, by XORing the cryptographic core output with the input. After the encryption/decryption, the ciphertext is XORed with the intermediate authentication result. The XORed result is used as input for the polynomial multiplication to create the next (intermediate) authentication result. For more information about the GCM protocol, see GCM Protocol Operation in Section 17.2.3.2.
Figure 17-10 AES - GCM OperationCCM Operation
Figure 17-11 shows one round of a CCM (counter with CBC-MAC) operation for encryption and decryption. A 32-bit counter is used as IV (as it is for CTR mode). The data is encrypted in the same way as in CTR mode, by XORing the cryptographic core output with the input. Immediately after the encryption operation, the plaintext is XORed with the intermediate authentication result. The XOR result is used as input for a second encryption operation to calculate the next (intermediate) authentication result.
Figure 17-11 AES - CCM Operation