5.2.1.2 ECDH - TempKey Source

The ECDH command may use the value in TempKey as its starting value for an ECDH command. The ECC private key value in TempKey must be generated by the GenKey command. Once the TempKey has been used by the ECDH command, the TempKey.Valid flag is reset. If the output is back to the TempKey location, then this flag will be set again.

Table 5-40. Input Parameters ECDH TempKey
Opcode (1 Byte)	Mode (1 Byte)	KeyId (2 Bytes)	Data		Description
Opcode (1 Byte)	Mode (1 Byte)	KeyId (2 Bytes)	Data 1 (32 Bytes)	Data 2 (32 Bytes)	Description
0x43	0x0D	0x00 00	X component of public key	Y component of public key	Results sent to the output buffer Output is in the clear⁽¹⁾
	0x0F	0x00 00	X component of public key	Y component of public key	Results sent to the output buffer Output is encrypted
	0x09	0x00 00	X component of public key	Y component of public key	Results stored in TempKey Output is available for other operations but is not directly accessible.
	0x05	0x00 0[Slot]	X component of public key	Y component of public key	Results stored in specified slot

Note:

When the ChipOptions.ECDHPROT value is 1, then the output of the ECDH command will be encrypted in this mode. For the ATECC608A-TNGLoRaWAN the ECDHPROT field is set to 0 and encryption will be dependent upon the mode of the ECDH command.

Table 5-41. Output Response ECDH TempKey
Name	Mode	Size	Description
Response	0x0D or 0x0F	1 byte	Error code if command fails
Response	0x0D	32 bytes	Shared Master Secret as clear text
Response OutNonce	0x0F	32 bytes 32 bytes	Shared Master Secret as encrypted text nonce used for encryption
Response	0x05 or 0x09	1 byte	0x00 if successful, otherwise an error code is returned

ATECC608A-TNGLoRaWAN

5.2.1.2 ECDH - TempKey Source