SLAU367P October 2012 – April 2020 MSP430FR5041 , MSP430FR5043 , MSP430FR50431 , MSP430FR5847 , MSP430FR58471 , MSP430FR5848 , MSP430FR5849 , MSP430FR5857 , MSP430FR5858 , MSP430FR5859 , MSP430FR5867 , MSP430FR58671 , MSP430FR5868 , MSP430FR5869 , MSP430FR5870 , MSP430FR5872 , MSP430FR58721 , MSP430FR5887 , MSP430FR5888 , MSP430FR5889 , MSP430FR58891 , MSP430FR5922 , MSP430FR59221 , MSP430FR5947 , MSP430FR59471 , MSP430FR5948 , MSP430FR5949 , MSP430FR5957 , MSP430FR5958 , MSP430FR5959 , MSP430FR5962 , MSP430FR5964 , MSP430FR5967 , MSP430FR5968 , MSP430FR5969 , MSP430FR5969-SP , MSP430FR59691 , MSP430FR5970 , MSP430FR5972 , MSP430FR59721 , MSP430FR5986 , MSP430FR5987 , MSP430FR5988 , MSP430FR5989 , MSP430FR5989-EP , MSP430FR59891 , MSP430FR5992 , MSP430FR5994 , MSP430FR59941 , MSP430FR6005 , MSP430FR6007 , MSP430FR6035 , MSP430FR6037 , MSP430FR60371 , MSP430FR6041 , MSP430FR6043 , MSP430FR60431 , MSP430FR6045 , MSP430FR6047 , MSP430FR60471 , MSP430FR6820 , MSP430FR6822 , MSP430FR68221 , MSP430FR6870 , MSP430FR6872 , MSP430FR68721 , MSP430FR6877 , MSP430FR6879 , MSP430FR68791 , MSP430FR6887 , MSP430FR6888 , MSP430FR6889 , MSP430FR68891 , MSP430FR6920 , MSP430FR6922 , MSP430FR69221 , MSP430FR6927 , MSP430FR69271 , MSP430FR6928 , MSP430FR6970 , MSP430FR6972 , MSP430FR69721 , MSP430FR6977 , MSP430FR6979 , MSP430FR69791 , MSP430FR6987 , MSP430FR6988 , MSP430FR6989 , MSP430FR69891
14.2.11.1.2 ECB Decryption
Figure 14-7 ECB Decryption To implement the ECB decryption without CPU interaction, two DMA channels are needed. Static DMA priorities must be enabled. The DMA triggers must be configured as level-sensitive triggers.
Table 14-4 AES DMA Configuration for ECB Decryption
| AES
CMEN |
AES
CMx |
AES
OPx |
DMA_A
Triggered by 'AES trigger 0' |
DMA_B
Triggered by 'AES trigger 1' |
|---|---|---|---|---|
| 1 | 00 | 01 or 11 | Read plaintext from AESADOUT | Write ciphertext to AESADIN, which also triggers the next decryption |
The following pseudo code snippet shows the implementation of the ECB decryption in software:
ECB_Decryption(key, plaintext, ciphertext, num_blocks)
// Pseudo Code
{
Generate Decrypt Key
Configure AES:
AESCMEN= 0; AESOPx= 10;
Write key into AESAKEY;
Wait until key generation completed.
Configure AES for block cipher:
AESCMEN= 1; AESCMx= ECB; AESOPx= 11;
AESKEYWR= 1; // Use previously generated key
Setup DMA:
DMA0: Triggered by AES trigger 0,
Source: AESADOUT, Destination: plaintext,
Size: num_blocks*8 words, Single Transfer mode
DMA1: Triggered by AES trigger 1,
Source: ciphertext, Destination: AESADIN,
Size: num_blocks*8 words, Single Transfer mode
Start decryption:
AESBLKCNT= num_blocks;
End of decryption: DMA0IFG=1
}