Digi NS9215 manual Nonce buffer, Bits, Contents

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. .

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:
	Bits	127:120	119:8*L-par	8*L-par-1:0
	Contents	reserved	Nonce	Message length

Processing flow This is the CCM buffer descriptor processing flow:

CCM Mode Encryption

CCM Mode Decryption

Source DMA

Operations

Key Buffer

Nonce

Additional

Authentication

Data (optional )

Data Buffer Pass

1 (authentication )

Data Buffer Pass

2 (encryption )

Destination DMA

Operations

Authentication

Code

Encrypted Data

Source DMA

Operations

Key Buffer

Nonce

Data Buffer Pass

1 (decryption )

Additional

Authentication

Data (optional )

Data Buffer Pass

2 (authentication )

Destination DMA

Operations

Decrypted Data

Authentication

Code

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