NRF52810-QFAA-R7 datasheet(107/483 Pages) NORDIC

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Peripherals

code (MAC)" is called the "Message integrity check (MIC)" in Bluetooth terminology and also in this

document.

The CCM block generates an encrypted keystream that is applied to input data using the XOR operation

and generates the 4 byte MIC field in one operation. The CCM and radio can be configured to work

synchronously. The CCM will encrypt in time for transmission and decrypt after receiving bytes into

memory from the radio. All operations can complete within the packet RX or TX time. CCM on this device

is implemented according to Bluetooth requirements and the algorithm as defined in IETF RFC3610,

and depends on the AES-128 block cipher. A description of the CCM algorithm can also be found in NIST

Special Publication 800-38C. The Bluetooth specification describes the configuration of counter mode

blocks and encryption blocks to implement compliant encryption for BLE.

The CCM block uses EasyDMA to load key, counter mode blocks (including the nonce required), and to

read/write plain text and cipher text.

The AES CCM supports three operations: key-stream generation, packet encryption, and packet

decryption. All these operations are done in compliance with the Bluetooth specification.14

key-stream

generation

KSGEN

encryption / decryption

CRYPT

ENDKSGEN

ENDCRYPT

SHORTCUT

Figure 26: Key-stream generation followed by encryption or decryption. The shortcut is optional.

6.4.1 Key-steam generation

A new key-stream needs to be generated before a new packet encryption or packet decryption operation

can be started.

A key-stream is generated by triggering the KSGEN task and an ENDKSGEN event will be generated when

the key-stream has been generated.

Key-stream generation, packet encryption, and packet decryption operations utilize the configuration

specified in the data structure pointed to by CNFPTR on page 115. It is necessary to configure this

pointer and its underlying data structure, and the MODE on page 114 register before the KSGEN task is

triggered.

The key-stream will be stored in the AES CCM’s temporary memory area, specified by the SCRATCHPTR on

page 116, where it will be used in subsequent encryption and decryption operations.

For default length packets (MODE.LENGTH = Default) the size of the generated key-stream is 27 bytes.

When using extended length packets (MODE.LENGTH = Extended) the MAXPACKETSIZE on page 116

must be greater or equal to the length of the subsequent packet payload to be encrypted or decrypted.

The maximum length of the key-stream in extended mode is 251 bytes, which means that the maximum

packet payload size is 251.

If a shortcut is used between ENDKSGEN event and CRYPT task, the INPTR on page 115 pointer and the

OUTPTR on page 115 pointers must also be configured before the KSGEN task is triggered.

6.4.2 Encryption

During packet encryption, the AES CCM will read the unencrypted packet located in RAM at the address

specified in the INPTR pointer, encrypt the packet and append a four byte long Message Integrity Check

(MIC) field to the packet.

14 Bluetooth AES CCM 128 bit block encryption, see Bluetooth Core specification Version 4.0.

4430_161 v1.0

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