Access Protection Scheme

AES and SHA IP in DTHE support two contexts, namely Public and Secure.

AES

The AES IP is an efficient implementation of the Rijndael cipher (the AES algorithm) and a 128-bit polynomial multiplication. Rijndael is a block cipher with each data block consisting of 128-bits.
AES encryption requires a specific number of rounds depending on the key length. Supported key lengths are 128-bit, 192-bit, and 256 bit, requiring 10, 12, and 14 rounds respectively; or 32, 38, and 44 clock cycles respectively because (# of clock cycles) = 2 + 3 x (# of rounds). The larger key lengths provide greater encryption strength at the expense of additional rounds and therefore reduced throughput.

AES functional diagram

AES ECB feedback mode

Above figure illustrates the basic Electronic Code Book (ECB) feedback mode of operation, where the input data is passed directly to the basic crypto core and the output of the crypto core is passed directly to the output buffer. For decryption the crypto core operates in reverse, thus, the decrypt datapath is used for the data processing, where encryption uses the encrypt datapath.

AES CBC feedback mode

Above figure illustrates the Cipher Block Chaining (CBC) feedback mode of operation, where the input data is XOR-ed with the initialization vector (IV) before it is passed to the basic crypto core. The output of the crypto core passes directly to the output buffer and becomes the next IV. For decryption, the operation is reversed, resulting in an XOR at the output of the crypto core. The input cipher text of the current operation is the IV for the next operation.

This sequence performs Encryption and decryption operations for AES-CBC/ECB algorithms. Supported key lengths are 128 and 256 bit.

DTHE_open(): Function to open DTHE instance, enable DTHE engine.
DTHE_AES_open(): Function to open DTHE AES instance using the handle returned from DTHE_open().
DTHE_AES_execute(): Function to execute the AES driver with specified parameters.
DTHE_AES_close(): Function to close DTHE AES driver.
DTHE_close(): Function to De-initialize the DTHE instance.

This sequence performs AES CMAC-128 and CMAC-256.

DTHE_open(): Function to open DTHE instance, enable DTHE engine.
app_aes_cmac128(): Function (defined in example) to calculate CMAC for input buffer. This is not supported directly through Hardware and hence a software implementation is available in the examples. However, for AES computation we use the DTHE
DTHE_close(): Function to De-initialize the DTHE instance.