SWCU194 March 2023 CC1314R10 , CC1354P10 , CC1354R10 , CC2674P10 , CC2674R10
The following software example in pseudo code, describes the actions that are typically executed by the Host software to authenticate a message, stored in external memory, with AES-CMAC-CBC-MAC mode. The result TAG is read via the slave interface.
The following sequence processes a packet of at least one input data byte.
// configure the master control module
write ALGSEL 0x00000002 // enable the DMA path to the AES engine
write IRQCLR 0x00000001 // clear any outstanding events
// configure the key store to provide a pre-loaded AES key
write KEYREADAREA 0x00000000 // load the key from ram area 0 (NOTE: The key
// must be pre-loaded to this area)
wait KEYREADAREA[31] == ’0’ // wait until the key is loaded to the AES module
check IRQSTAT[29] == ‘0’ // check that the key is loaded without errors
// write the KEY2
write AESKEY2_0
...
write AESKEY2_3
// write the KEY3
write AESKEY3_0
...
write AESKEY3_3
// write the initialization vector
write AESIV_0
...
write AESIV_3
// configure the AES engine
write AESCTL = 0b0010_0010_0000_0000_0000_0000_0000_1100 // program AES-XCBC-
// MAC-128 authentication
write AESDATALEN0 // write length of the crypto block (lo)
write AESDATALEN1 // write the length of the crypto block (hi)
// (may be non-block size aligned)
// configure DMAC
write DMACH0CTRL 0x000000001 // enable DMA channel 0
write DMACH0EXTADDR <address> // base address of the input data in ext. memory
write DMACH0DMALENGTH <length> // input data length in bytes, equal to the
// message length
// len({AAD data, pad, crypto_data, pad})
// (may be non-block size aligned)
// wait for completion
wait IRQSTAT[0] == ’1’ // wait for operation completed
check IRQSTAT[31] == ‘0’ // check for the absence of errors
write ALGSEL 0x00000000 // disable master control/DMA clock
// read tag
wait AESCTL[30] == ’1’ // wait for the SAVED_CONTEXT_RDY bit [30]
read AESTAGOUT_0
...
read AESTAGOUT_3 // this read clears the SAVED_CONTEXT_RDY flag
// end of algorithm