NRF52810-QFAA-R datasheet(108/483 Pages) NORDIC

108 / 483 page

Peripherals

Encryption is started by triggering the CRYPT task with the MODE on page 114 register set to

ENCRYPTION. An ENDCRYPT event will be generated when packet encryption is completed

The AES CCM will also modify the length field of the packet to adjust for the appended MIC field, that is,

add four bytes to the length, and store the resulting packet back into RAM at the address specified in the

OUTPTR on page 115 pointer, see Encryption on page 108.

Empty packets (length field is set to 0) will not be encrypted but instead moved unmodified through the

AES CCM.

The CCM supports different widths of the LENGTH field in the data structure for encrypted packets. This is

configured in the MODE on page 114 register.

AES CCM

RFU

EPL

L+4 RFU

Unencrypted packet

Encrypted packet

MIC

Scratch area

CCM data

structure

MODE = ENCRYPTION

H: Header (S0)

L: Length

RFU: reserved for future use (S1)

PL: unencrypted payload

EPL: encrypted payload

INPTR

OUTPTR

SCRATCHPTR

CNFPTR

Figure 27: Encryption

6.4.3 Decryption

During packet decryption, the AES CCM will read the encrypted packet located in RAM at the address

specified in the INPTR pointer, decrypt the packet, authenticate the packet’s MIC field and generate the

appropriate MIC status.

Decryption is started by triggering the CRYPT task with the MODE on page 114 register set to

DECRYPTION. An ENDCRYPT event will be generated when packet decryption is completed

The AES CCM will also modify the length field of the packet to adjust for the MIC field, that is, subtract

four bytes from the length, and then store the decrypted packet into RAM at the address pointed to by the

OUTPTR pointer, see Decryption on page 108.

The CCM is only able to decrypt packet payloads that are at least 5 bytes long, that is, 1 byte or more

encrypted payload (EPL) and 4 bytes of MIC. The CCM will therefore generate a MIC error for packets

where the length field is set to 1, 2, 3 or 4.

Empty packets (length field is set to 0) will not be decrypted but instead moved unmodified through the

AES CCM, these packets will always pass the MIC check.

The CCM supports different widths of the LENGTH field in the data structure for decrypted packets. This is

configured in the MODE on page 114 register.

AES CCM

RFU

EPL

L+4 RFU

Unencrypted packet

Encrypted packet

MIC

Scratch area

CCM data

structure

MODE = DECRYPTION

H: Header (S0)

L: Length

RFU: reserved for future use (S1)

PL: unencrypted payload

EPL: encrypted payload

OUTPTR

INPTR

SCRATCHPTR

CNFPTR

Figure 28: Decryption

6.4.4 AES CCM and RADIO concurrent operation

The CCM module is able to encrypt/decrypt data synchronously to data being transmitted or received on

the radio.

4430_161 v1.0

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