7.2.4.8.1 Manual Mode
The sequence of actions is as follows:
- Write AES_MR with all required fields, including but not limited to SMOD and OPMOD. (Write AES_EMR.PKRS according to the type of key to be loaded).
- Write the 128-bit/192-bit/256-bit AES key in AES_KEYWRx or in the Private Key internal registers.
- Write the initialization vector (or counter) in
AES_IVRx.Note: AES_IVRx concerns all modes except ECB.
- Set the bit DATRDY (Data Ready) in the AES Interrupt Enable register (AES_IER), depending on whether an interrupt is required or not at the end of processing.
- Write the data to be encrypted/decrypted in the authorized AES_IDATARx (see the following table).
- Set the START bit in the AES Control register (AES_CR) to begin the encryption or the decryption process.
- When processing completes, the DATRDY flag in the AES Interrupt Status register (AES_ISR) is raised. If an interrupt has been enabled by setting AES_IER.DATRDY, the interrupt line of the AES is activated.
- When software reads one of AES_ODATARx, AES_IER.DATRDY is automatically cleared.
Operating Mode | Input Data Registers to Write |
---|---|
ECB | All |
CBC | All |
OFB | All |
128-bit CFB | All |
64-bit CFB | AES_IDATAR0 and AES_IDATAR1 |
32-bit CFB | AES_IDATAR0 |
16-bit CFB | AES_IDATAR0 |
8-bit CFB | AES_IDATAR0 |
CTR | All |
GCM | All |
XTS | All |
Note:
- In 64-bit CFB mode, writing to AES_IDATAR2 and AES_IDATAR3 is not allowed and may lead to errors in processing.
- In 32, 16, and 8-bit CFB modes, writing to AES_IDATAR1, AES_IDATAR2 and AES_IDATAR3 is not allowed and may lead to errors in processing.