Output in the Arduino Serial Monitor.

Important things to know about ECC signatures:

1. ECC signatures are created using a secret private key and the elliptical curve algorithm. For the purpose of

this example, we can just ignore the printout of the keys public key at the top - this is part of the

device is created, stored and locked up inside the device.

2. ECC signatures are 64 bytes long.

3. Contrary to most definitions of signatures, ECC signatures are different every time! ECCs include intentional

randomness in the calculation, and so it will always produce a new unique signature. However, every

signature that it creates will pass verification (as we will later see in example 3). Try hitting reset on your

4. With the ATECC508A, we can only send it 32 bytes of data to sign. If you need to sign something larger,

then it is recommended that you create a 32-byte hash of the data first, then you can sign the hash.

Basically, when you send a bunch of data into a hashing algorithm (such as SHA256), it will always respond

with a unique 32 byte digest. It is very similar to creating a digital signature, however it does not require a

key, so anyone can calculate the hash of any data. You may find that for many projects, 32 bytes is enough

data, so for now, there's no need to pursue hashes.

The Code

Now lets take a quick look at the important parts of the example code. There are two things worthy of note:

At the very top, we define the message we want to sign.

// array to hold our 32 bytes of message. Note, it must be 32 bytes, no more or less.

uint8_t message[32] = {

0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0A, 0x0B, 0x0C, 0x0D, 0x0E, 0x0F

,

0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18, 0x19, 0x1A, 0x1B, 0x1C, 0x1D, 0x1E, 0x1F

};

Not much to say here, other than it's a nice array of 32 unsigned 8 bit integers. We chose to make the values

simply count from 0 to 32, but these could really be anything.