CCM data structure

The CCM data structure is located in data RAM, at the memory location specified by the CNFPTR pointer register.

Table 1. CCM data structure overview
Property	Address offset	Description
KEY	0	16-byte AES key.
PKTCTR	16	Octet0 (least significant octet (LSO)) of packet. counter
	17	Octet1 of packet counter.
	18	Octet2 of packet counter.
	19	Octet3 of packet counter.
	20	Bit 6 – bit 0: Octet4 (7 most significant bits of packet counter, with bit 6 being the most significant bit). Bit 7: Ignored.
	21	Ignored.
	22	Ignored.
	23	Ignored.
	24	Bit 0: Direction bit. Bit 7 – bit 1: Zero padded.
IV	25	8-byte initialization vector (IV). Octet0 (LSO) of IV, Octet1 of IV, … , Octet7 (MSO) of IV.

The NONCE vector (as specified by the Bluetooth Core Specification) will be generated by hardware based on the information specified in the CCM data structure.

Table 2. Data structure for unencrypted packet
Property	Address offset	Description
HEADER	0	Packet header
LENGTH	1	Number of bytes in unencrypted payload
RFU	2	Reserved for future use
PAYLOAD	3	Unencrypted payload

Table 3. Data structure for encrypted packet
Property	Address offset	Description
HEADER	0	Packet header
LENGTH	1	Number of bytes in encrypted payload including length of MIC LENGTH will be 0 for empty packets since the MIC is not added to empty packets
RFU	2	Reserved for future use
PAYLOAD	3	Encrypted payload
MIC	3 + payload length	ENCRYPT: 4 bytes encrypted MIC MIC is not added to empty packets