SWCU194 March 2023 CC1314R10 , CC1354P10 , CC1354R10 , CC2674P10 , CC2674R10
The following software example in pseudocode describes the actions that are typically executed by the host software to encrypt and authenticate a message (AAD and payload data), stored in external memory, with AES-CCM mode. The encrypted result is placed into a pre-allocated area in external memory. The result TAG is read using the slave interface.
The following sequence processes a packet of at least 1 byte of AAD data and at least 1 crypto 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 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 initialization vector
write AESIV_0
...
write AESIV_3
// configure the AES engine
write AESCTL = 0b0010_0000_0101_1100_0000_0000_0100_1100 // program AES-CCM-128
// encryption (M=1, L=3)
write AESDATALEN0 // write the length of the crypto block (lo)
write AESDATALEN1 // write the length of the crypto block (hi)
// (may be non-block size aligned)
write AESAUTHLEN // write the length of the AAD data block (may be non-block size aligned)
// configure DMAC to fetch the AAD data
write DMACH0CTL 0x000000001 // enable DMA channel 0
write DMACH0EXTADDR <address> // base address of the AAD input data in ext. memory
write DMACH0LEN <length> // AAD data length in bytes, equal to the AAD length len({aad data})
// (may be non-block size aligned)
// wait for completion of the AAD data transfer
wait IRQSTAT[1] == ’1’ // wait for DMA_IN_DONE
check IRQSTAT[31] == ‘0’ // check for the absence of errors
// configure DMAC
write DMACH0CTL 0x000000001 // enable DMA channel 0
write DMACH0EXTADDR <address> // base address of the payload data in ext. memory
write DMACH0LEN <length> // payload data length in bytes, equal to the
// message length len({crypto_data})
write DMACH1CTL 0x000000001 // enable DMA channel 1
write DMACH1EXTADDR <address> // base address of the output data buffer
write DMACH1LEN <length> // output data length in bytes, equal to
// the result data length len({crypto data})
// 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 the 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