SWCU192 November 2021 CC1312R7 , CC1352P7 , CC2652P7 , CC2652R7
For AES-GCM operations, the following configuration parameters are required:
The AES module is used in the mode where it calculates the Y0 encrypted and H (hash key) internally based on cipher key from the key-store module.
The AAD and cryptographic data may end misaligned. In this case, the module internally pads both sets of data to a 128-bit boundary with zeroes. Padding is done as follows: the AAD and crypto data padding satisfies the bit string: 0n, with 0 ≤ n ≤ 127 such that the input AAD and data block lengths including padding are 128-bit aligned. The AAD data must be transferred to the AES engine with a separate DMA operation (it may not be combined with the payload data) or using slave transfers.
The length field can have any value. If a data stream is done and the next data stream uses the same key and control, only the IV and length fields can be written with a new value. It is not allowed to write both length fields with zeroes. A GCM operation cannot be interrupted. The result TAG is typically read through the slave interface, but can also be written to an external memory location through a separate DMA operation.