Digi NS9215 - Manual (Page 361)

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A E S D A T A E N C R Y P T I O N / D E C R Y P T I O N M O D U L E
CCM mode
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For encryption, software must set up this buffer descriptor sequence: Key,
Nonce, additional data (optional), data (used to compute the authentication
code), data (used to perform the actual encryption).
For decryption, software must set up this buffer descriptor sequence: Key,
Nonce, Data (used to perform the actual decryption), Additional data
(optional), Data (used to compute the authentication code).
Note:
The data must be DMA’ed through the AES module twice in CCM mode for
both encryption and decryption modes.
Nonce buffer
This is the format of the Nonce buffer:
Processing flow
This is the CCM buffer descriptor processing flow:
Bits 127:120 119:8*L-par 8*L-par-1:0
Contents reserved Nonce Message length
Key Buffer
Data Buffer Pass
1
(authentication )
Additional
Authentication
Data
(optional )
Nonce
Data Buffer Pass
2
(encryption )
Authentication
Code
Encrypted Data
Source DMA
Operations
Destination DMA
Operations
CCM Mode Encryption
Key Buffer
Data Buffer Pass
2
(authentication )
Additional
Authentication
Data
(optional )
Nonce
Data Buffer Pass
1
(decryption )
Authentication
Code
Decrypted Data
Source DMA
Operations
Destination DMA
Operations
CCM Mode Decryption