ATECC608A datasheet(43/81 Pages) MICROCHIP

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Table 5-48. Input Parameters - Sign External

Opcode

(1 Byte)

Mode

(1 Byte)

KeyId

(2 Bytes)

Description

0x41

0x80 or 0xC0

0x00 0[Slot]

External message digest stored in TempKey

0xA0 or 0xD0

0x00 0[Slot]

External message digest stored in Message Digest Buffer

Table 5-49. Output Response - Sign External

Name

Size

Description

Response

1 byte

Error code if the command fails

64 bytes

The signature composed of R and S values

5.2.4

Verify Command

The Verify command takes an ECDSA [R,S] signature and verifies that it is correctly generated given an input

message digest and public key. In all cases, the signature is an input to the command.

An optional MAC can be returned from the Verify command to defeat any man-in-the-middle attacks. If the verify

calculation shows that the signature is correctly generated from the input digest, then a MAC will be computed based

on an input nonce stored in TempKey and the value of the IO protection secret which is stored in both the

ATECC608A-TNGLoRaWAN and the host MCU. MAC outputs can only be generated in External and Stored modes.

The IO protection function must be enabled for MAC computation.

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.

2.1.

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.

2.2.

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:

4.1.

One byte success, fail or error code if MAC is not required.

4.2.

A 32-byte MAC if specified by the mode.

ATECC608A-TNGLoRaWAN

Device Commands

Complete Datasheet

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