AES block processing

AN3270

16/23

Doc ID 17919 Rev 2

Figure 12.

Encryption using Cipher Block Chaining (CBC) mode

Figure 13.

Decryption using Cipher Block Chaining (CBC) mode

Chaining modes (CBC, CFB, OFB and CTR) are not implemented in hardware. A firmware

implementation of block chaining modes (ECB, CBC, CFB, OFB and CTR) using the AES

hardware accelerator is provided in the aes_util.c/.h files with this application note.

As an example, the prototype of CBC mode is as follows:

AES_Encrypt_CBC(): Encrypt plain text with encryption key providing cipher text using

CBC chaining mode. Encryption status is returned by the function.

ErrorStatus AES_Encrypt_CBC(PlainText, /* address of plain text to be encrypted */

CipherText, /* address of buffer that used to store the cipher text */

EncryptionKey, /* address of key used to encrypt plain text */

InitVector, /* address of initialization vector */

TextSize); /* size of padded plain text */

For the implementation of other chaining modes, refer to the aes_util.c/.h files.