5.2.4.1 Verify - External Public Key Mode

The Verify command may be used to verify a message generated externally to the ATECC608A-TNGLoRaWAN with a public key that is passed to the command. The output of the command will either be a code indicating success, failure or error or a 32-byte MAC. Prior to this command being run, the message should be written using the Nonce command in Fixed mode to either TempKey or the Message Digest Buffer. In this mode, the device merely accelerates the public key computation and returns a boolean result.

Procedure to Verify a Message with an External Public Key

Write the 32-byte digest of the message to either the TempKey or Message Digest Buffer using the Nonce command in Fixed mode.
Optional: System Nonce - Nonce generated by the system.
1. If the external message digest is stored in TempKey, the nonce generated by the system must be stored in the lower 32 bytes of the Message Digest Buffer.
2. If the external message is stored in the MessageDigestBuffer[31:0], then the System Nonce must be stored in the upper 32 bytes of the MessageDigest Buffer[63:32]. To do this, the external message and nonce value should be written as a 64-byte value.
Issue the Verify command. Include the Mode, KeyID, which specifies the P256 ECC Curve, the 64-byte signature and the 64-byte external public key.
The output will return:
1. One byte success, fail or error code if MAC is not required.
2. A 32-byte MAC if specified by the mode.

Table 5-50. Command Parameters
Opcode (1 Byte)	Mode (1 Byte)	Key ID (2 Bytes)	Data Field (128 Bytes)		Comment
Opcode (1 Byte)	Mode (1 Byte)	Key ID (2 Bytes)	Signature (64 Bytes)	Public Key (64 Bytes)	Comment
0x45	0x02	0x00 04	R value S value	X value Y value	Message stored in TempKey
	0x22	0x00 04	R value S value	X value Y value	Message stored in Message Digest Buffer
	0xA2	0x00 04	R value S value	X value Y value	Message stored in TempKey System Nonce stored in MDB[31:0] Validation MAC is returned
	0x82	0x00 04	R value S value	X value Y value	Message stored in Message Digest Buffer System Nonce stored in MDB[63:32] Validation MAC is returned

Table 5-51. Output Response - Verify External
Name	Mode	Size	Response
Response	0x02 or 0x22	1 byte	0x00 - If signature is verified 0x01 - If signature does not match Error code - If there is a failure due to some other reason
Response	0x82 or 0xA2	1 byte or 32 bytes	Validation MAC - If signature is verified 0x01 - If signature does not match Error code - If there is a failure due to some other reason

Table 5-52. Validation MAC - Verify External
Size (Bytes)	Message in TempKey	Message in Message Digest Buffer
32	Contents of the IO protection key	Contents of the IO protection key
32	Message stored in TempKey	Message stored in the first 32 bytes of the Message Digest Buffer
32	System Nonce stored in the first 32 bytes of the Message Digest Buffer	System Nonce stored in the second 32 bytes of the Message Digest Buffer
32	R Data of the passed signature	R Data of the passed signature
32	S Data of the passed signature	S Data of the passed signature
1	Opcode	Opcode
1	Mode	Mode
2	Param2 [LSB,MSB]	Param2 [LSB,MSB]