Cryptographic Co-Processor ATECC508A (Qwiic) Hookup Guide

Introduction

The SparkFun Cryptographic Co-processor Breakout ATECC508A (Qwiic) takes all the great features of the Microchip ATECC508A Cryptographic Authentication Device and adds two Qwiic ports for plug and play functionality. In this tutorial we will cover the fundamentals of cryptographic authentication and how to use the ATECC508A to add a very high level of security to your projects.

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The ATECC508A is capable of many cryptographic processes. This tutorial focuses on Elliptic-curve cryptographic digital signatures (ECC) - using asymetric private/public keys. If those last few words are new to you, please read on! We will spend some time explaining in a bit.

At a very high level, the purpose of using this chip is to (1) verify that the message received actually came from the true sender and (2) verify that the data received was not tampered with. This technology is used in hyper-critical devices such as rocket launches, medical devices, two factor authentication keys (2FA), ink cartridges, garage door openers and car key FOBs.

Probably it's most important feature: this device can securely store a private ECC key. In fact, this private key will never be accessible - not even to you, the owner. It is created internally on the chip during configuration, and it can never be read from the chip (even if your de-capped the chip). Although you will never know it, you can still command the co-processor to use the secret private key to create a unique signature on some data. With this functionality, it can be used to securely authenticate a message in any kind of communication system. For example, between systems such as a node in an IoT system. Follow along, and you'll be creating 64 byte signatures (yes, bytes) and verifying them securely in no time!

Required Materials

To follow along with this tutorial, you will need the following materials that are included in the kit. You may not need everything though depending on what you have. Add it to your cart, read through the guide, and adjust the cart as necessary.

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Suggested Reading

If you aren’t familiar with the following concepts, we recommend you read over these tutorials before continuing.

Cryptographic Authentication

Cryptography is a large subject matter. There many different types of cryptographic processes, each with their own different purpose and type of math. In this tutorial, we are focusing on cryptographic authentication. On a very high level, this usually involves data, digital signatures and verification. First, we must understand what a digital signature is and how it is created. Second we must understand verification which includes the use of a private/public key pair. Let's jump into digital signatures!

Digital signatures

A digital signature is quite similar to a hand-written signature. After you write a letter, you add your signature at the bottom. Just like the hand-written signature, a digital signature is added to your data. When we say "added" we mean that it is included as a separate chunk of data. So when sending some data with a digital signature, you would send the data as one piece of data, and then you would also send the digital signature as a separate piece of data. So this is the first difference to understand: digital signatures are like hand-written signatures, except they don't live on the same piece of paper (they are a separate chunk of data).

Another big difference: to create a digital signature, you need a bit more than a pen. You actually need three things:

1. Data: This is the data you want to sign. For this co-processor, we are going to sign 32 bytes of data. This is essentially your "letter without a signature".
2. A Key: Is simply a unique chunk of data. The key lives on a protected part of the co-processors memory. It was created during configuration. We will never have access to it. The idea of a single digital key is pretty straight forward. It parallels the physical door key quite well. The chunk of data is unique, just like the grooves and cuts of a physical key are unique.
3. An Algorithm: The complex math that we will offload to the co-processor. It is a particular type of cryptographic math called Elliptic Curve Cryptography (ECC). Using our data and key, this algorithm will output a digital signature.

One more thing: digital signatures will be different when you change your message. This is pretty different than the traditional idea of a signature. When we think of hand-written signatures, we think that the entire purpose is for it to be exactly the same every time. The author should be the only one who can hold the pen like so and make that unique signature. With digital signatures we need to think a bit differently. Remember that we are sending our message (and a key) into an algorithm. This will result in a new and different signature if the message or key changes. In most cases, a digital signature is always unique from all other previous digital signatures.

So that was easy enough, right? Good. Digital signatures aren't so scary now. But what would we want to do with one of these? Verify it.

Verification

Verification of a digital signature is quite similar verifying a hand-written signature. In both cases, we want to determine if the signature is authentic. With a hand-written signature, you might just use your eyes to see if it looks correct. With a digital signature we need to use a bit more than our eyes. We need the data, the signature, a key, and an algorithm (sound familiar?). Simple enough, right? Well this is where it starts to get slightly more complex. We need to understand one more concept: the idea of key pairs.

Up until this point, we have called the "key" simply a "key", but to be more accurate, this should be called the private key. And it is part of a key pair. When we configure the co-processor it actually creates a key pair which includes two keys: one private key and one public key. These two keys work together, and they allow us to sign and verify signatures. We use the private key to sign the data, and we use the public key to verify data. This is also known as an asymetric cryptographic process.

Now that we're talking private and public key pairs, let's clearly define what we need to create a digital signature, and what we need to verify a digital signature:

From Alice to Bob

Although you can accomplish a few neat things using only one of these chips (signing data, verifying signatures, creating high-quality random numbers, etc.), the truly powerful communication security starts when you have two of them (we will refer to them as Alice and Bob).

Our Arduino library utilizes the old story of Alice, Bob and Eve. If you read up on cryptography, you will often come across these names. Alice and Bob are always trying to have a private conversation, but Eve keeps eavesdropping (and sometimes trying to impersonate Alice). So Alice and Bob start using cryptography to keep Eve out of the mix.

Side note: In a lot of traditional examples, Alice and Bob are encrypting and decrypting their messages. I want to highlight here again, that this chip utilizes a different cryptographic tool: authentication. With the ATECC508A, we can create and verify signatures. The message is still sent out in the open/public for Eve to clearly read. However, Eve will never have Alice's private key and could never create a valid signature (to authenticate the message). Therefore, Eve can never pretend to be Alice!

In our examples, Alice is sending a message to Bob. Alice can use her own co-processor to create a digital signature. She can then send her message and signature to Bob. Bob can then use his own separate co-processor to verify the message and signature.

If you are brand new to cryptography, take a minute to watch the above gif loop a couple times. It shows the basic steps necessary to have an authenticated message from Alice to Bob. The use of a private/public key pair can be a bit daunting at first sight, but after going through this tutorial, we hope it can become a piece of cake.

Hardware Overview

Power

There is a power status LED to help make sure that your Cryptographic Co-processor Breakout is getting power. You can power the board either through the polarized Qwiic connector system or the breakout pins (3.3V and GND) provided. This Qwiic system is meant to use 3.3V, be sure that you are NOT using another voltage when using the Qwiic system.

LED

The board includes a red power LED to indicate you have power plugged in properly. Note, there is a jumper on the back to disconnect this from the circuit. This is useful if you really want to conserve current consumption on your system.

ATECC508A Cryptographic Co-Processor

The co-processor on this board is the Microchip ATECC508A. It's primary features include creating/storing ECC keys, creating digital signatures and verifying them. It is also capable of doing many other cryptographic processes includeing SHA-256 hash, Diffie-Hellman Key Exchange, and high quality random number generation. For more details on the ATECC508A cryptographic chip, check out the datasheet.

Connections

We've included two qwiic connectors for plug and play operation.

It also has the pins broken out to 0.1-inch PTH headers, if you'd like a more permanent (soldered) connection to the I²C lines.

Jumpers

There are two jumpers on this board. The first, connects pull-up resistors to the I²C bus and the other connects the power to the PWR status LED.

Board Dimensions

For those interested, the basic board dimensions are shown below, all measurements are in inches and the grid spacing is 0.1". The SparkFun Cryptographic Co-processor PCB itself, measures (approximately) 1x1 inch. Additionially, we have provided a PDF of the dimensional drawing, if necessary.

Hardware Hookup

With the Qwiic connector system, assembling the hardware is fairly simple. For the examples below, all you need to do is connect your Cryptographic Co-Processor Breakout to a RedBoard Artemis with a Qwiic cable. Otherwise, you can use the I²C pins, if you don't have a Qwiic connector on your microcontroller board. Just be aware of your input voltage and any logic level shifting you may need to do. (*Don't forget to plug the Artemis into a computer with a USB-C cable.)

Note, the setup shown here is used for the configuration example and the single-board examples (1,2,3 and 5). For the more advanced examples that involve Alice and Bob (Example 4 and Example 6), you will need to setup two Artemis boards - each with their own co-processor. Additional hardware hookup instructions are included at those sections.

Software Setup

Installing Arduino

If you haven't used the Arduino IDE before, head on over to our Installing the Arduino IDE tutorial to get set up:

Getting the Arduino Library

To make Configuration and start using your Cryptographic Co-processor, we have written an Arduino Library. It currently supports only the Artemis board family. This is because some of the commands to the Co-processor require a larger I2C buffer. You have two options to install this library:

Setting up the Artemis Board

In case you haven't checked out the hookup guide for the RedBoard Artemis, we suggest reviewing it as the features are very different from your standard Arduino Uno.

Installing Artemis Board Package

This tutorial and Arduino Library support the Artemis Boards. You will need to use the Boards manager to install the necessary packages. You can visit the specific section of the Artemis tutorial here, or read the entire tutorial in the link below:

CH340 Driver Installation for the RedBoard Artemis

Don't forget, if you've never connected an CH340 device to your computer before, you may need to install drivers for the USB-to-serial converter. Check out our section on How to Install CH340 Drivers for help with the installation.

Arduino Library

We've written a library to easily get setup and start using the Cryptographic Co-processor ATECC508A. If you'd like to jump right into signing and verifying, then feel free to skip ahead to Example 1: Configuration However, it's not a bad idea to familiarize yourself a bit with the source code behind the examples, so let's take a closer look at the available functions in the library. You can install this library through the Arduino Library Manager. Search for SparkFun_Cryptographic and you should be able to install the latest version. If you prefer manually downloading the libraries from the GitHub repository, you can grab them here:

Let's get started by looking at the functions that set up the ATECC508A.

Setup

.begin() or .begin(i2caddr, TwoWire)

Communication

.wakeUp()

.idleMode()

.receiveResponseData(uint8_t length, boolean debug)

.checkCount(boolean debug)

.checkCrc(boolean debug)

.atca_calculate_crc(uint8_t length, uint8_t *data)

.sendCommand(uint8_t command_opcode, uint8_t param1, uint16_t param2, uint8_t *data, size_t length_of_data)

.read(uint8_t zone, uint16_t address, uint8_t length, boolean debug)

.write(uint8_t zone, uint16_t address, uint8_t *data, uint8_t length_of_data)

Configuration

.writeConfigSparkFun()

.lockConfig()

.lockDataAndOTP()

.lockDataSlot0()

.lock(uint8_t zone)

.readConfigZone()

.createNewKeyPair(uint16_t slot)

Sign and Verify

.createSignature(uint8_t *data, uint16_t slot)

.verifySignature(uint8_t *message, uint8_t *signature, uint8_t *publicKey)

Random Number Generator

.random(long max)

.random(long min, long max)

.getRandomByte(boolean debug)

.getRandomInt(boolean debug)

.getRandomLong(boolean debug)

.updateRandom32Bytes(boolean debug)

Example 1: Configuration

This example shows how to setup your Cryptographic Co-processor with SparkFun's standard settings. This will allow you to sign data and verify data with external signatures. The type of private keys we use in all of these examples are ECC. We have also included an example to use the random number generator and a challenge example. Beyond these functions, you may need to start with a different custom configuration.

To configure, upload Example1_Configuration.ino and open a serial terminal at 115200 baud. If communication with a fresh chip is successful, your Artemis will print out some useful information about your chip.

It will then prompt you to type a y to configure your device. Note, if you do not wish to configure your device, you can simply unplug at this time. Also, did we mention yet, that if you type a y, there's no going back.

Example 2: Sign

This example shows how to create a digital signature. To try it out, simply upload the Example2_Sign.ino, and watch your serial terminal at 115200 baud. Note, you may need to hit reset.

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 printInfo() function. As a side note, we will never know the devices private key. The private key for this 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 Artemis a few times and watch the signature values change. Same message + same private key = new signature.

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.

language:c
// 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.

language:c
//Let's create a digital signature!
atecc.createSignature(message); // by default, this uses the private key securely stored and locked in slot 0.

Well, the comments say it all, but I will mention that by sending the argument "message", we are sending a pointer to the first index (0), of the array. createSignature actually does 4 things for us under the hood:

1. Loads the message into the co-processor's memory location on the chip called tempKey.

2. Commands the co-processor to sign the contents of tempKey.

3. Receives the 64 byte signature and stores it in a public variable accessible at atecc.signature. Note, we created an instance of the ATECCX08A class with the name atecc, but you could choose something different, and then you'd need to modify how you access this signature array.

4. Prints a nice ready to compile serial debug message showing the signature. Handy for copying and pasting between code.

Example 3: Verify

This Example shows how to verify a signature. In order for the co-processor to do this, it needs three things:

1. Public Key (of the sender)
2. Message
3. Signature

If you have just completed Example2_sign, then you should remember seeing these 3 things printed out on the serial terminal. Before uploading Example3_verify.ino, please ensure you update the public key, message and signature at the top of the sketch.

Also very important: you will need to rename the publicKey[64] array at the top to publicKeyExternal[64]. This is what we will use to verify the message and signature, and so we must clarify that it is external.

Before uploading Example3_Verify.ino, we encourage you to click on the .gif below and watch a couple times. This can help show exactly what to do.

The Code

The fresh code that you see when you open up Example3_Verify.ino has place holders. Notice how all the bytes in each array is simply a bunch of 0x00s.

language:c
uint8_t publicKeyExternal[64] = {
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00
};

uint8_t message[32] = {
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00
};

uint8_t signature[64] = {
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00
};

You will need to delete these and paste in your own unique arrays. You could type them in manually, but it will be much easier to copy and paste them from the terminal output from Example 2.

Also note, when you highlight text within an Arduino serial monitor window, you must use the keyboard to actually copy them (Ctrl + C). It won't let you right-click to copy.

And the actual verification of the signature happens as a single function call. It is located at the bottom of setup().

language:c
// Let's verirfy!
if (atecc.verifySignature(message, signature, publicKeyExternal)) Serial.println("Success! Signature Verified.");
else Serial.println("Verification failure.");

atecc.verifySignature(message, signature, publicKeyExternal) is the actual call. This function will return a boolean true if all three things are good, and a false if something doesn't add up. If you change a single bit in any three of the arguments, then it won't verify.

Two nice things to thing about:

1. The only place in the world that could create the signature that will verify (using this public key) is inside your one unique co-processor. No one else in the world would ever be able to impersonate it. Pretty cool huh!

2. If any of the message was changed (even just a single bit flipped), then this verification would fail. This means that you can be very confident that the message was transmitted and received properly. In this way it is acting as a very robust checksum. It also means that if someone actually intercepted this message, they won't be able to change anything in the message. Sweet!

Example 4: From Alice to Bob

Hardware hookup

For Example 4, you will need to setup two Artemis boards with two co-processors, and connect a couple jumper wires between them. Using the Artemis Redboard, there is no soldering required for this setup.

Connect both of your Artemis boards to your computer using USB-C cables. Connect a Cryptographic Co-processor to each board using a Qwiic cable.

The board on the left is Alice. The board on the right is Bob. Connect Alice's TX1 pin to Bob's RX1 pin. Also connect GND to GND for good measure.

Note, both Alice and Bob need their own co-processor. So you're complete setup should look something like this:

Code setup

We will need to copy/paste Alice's public Key into the top of Bob's Sketch. First upload Alice's sketch to Alice, then watch her terminal at 115200. Copy her public key.

Now go over to Bob's sketch. Delete the place holder "blank" public key at the top, and paste in Alice's public key. Upload Bob's sketch to Bob.

Now watch both Alice's and Bob's terminal at 115200. Type a y into Alice's terminal, and she will send a signed message to Bob. Watch Bob's terminal. He will receive the message and verify it.

Watch this looped video to see it all happen. (click to enlarge).

Things to note about this:

1. We are now using two separate co-processors! In this example, Bob is simply using his co-processor as a verification engine. This could be accomplished by any computer that can compute ECC signature verification. But it's really quite nice to offload this calculation to a co-processor, and it will perform the calculations very fast.

2. Alice signed her message with her private key and she gave her public key to Bob. Hopefully the private vs public thing is starting to sink in.

3. Bob used an external public key (Alice's) to verify the authenticity of Alice. He could potentially name this anything he wants. And he could store lots of them, if he wanted to be able to verify messages from other senders.

4. Alice will most likely make her public key truly public and let everyone know about it. Once everyone has it, then she can send authenticated messages to anyone she likes, and they will truly know that it came from Alice.

5. It does not have to be a one-way street. The example could easily be reversed and Bob could give Alice his public key. When they both have shared their public key with the other, they can both send and verify.

The Code

As mentioned above, this example has two sketches. The purpose of splitting it up allows us to build upon the first three examples, and communicate securely between two completely separate systems.

Alice's sketch is actually quite similar to the Example2_Sign.ino, although it also sends the message and signature out it's TX1 pin.

Let's take a closer look at the important stuff within Alice's sketch:

language:c
//Let's create a digital signature!
atecc.createSignature(message); // by default, this uses the private key securely stored and locked in slot 0.

// Now let's send the message to Bob.
// this will include three things:
// (1) start header ("$$$") ASCII "$" = 0x24 HEX
// (2) message (32 bytes)
// (3) signature (64 bytes)

// start header
Serial1.print("$$$");

// message
// note, we use "Serial.write" because we are sending bytes of data (not characters)
for (int i = 0; i < sizeof(message) ; i++) Serial1.write(message[i]);

// signature
// Note, in Example4_Alice we are printing the signature we JUST created,
// and it lives inside the library as a public array called "atecc.signature"
for (int i = 0; i < sizeof(atecc.signature) ; i++) Serial1.write(atecc.signature[i]);

At the top of this code block, you can see she is using atecc.createSignature(message), just like in Example2_sign.

Then Alice sends everything to Bob, including a start "header" ($$$). This is simply used to avoid errors during transmission and helps ensure that Bob hears the entire message.

One important thing to note is that when Alice sends her message and signature to Bob, she uses the Serial1.write() function, because she is sending data (not ASCII characters).

Now let's take a closer look at the important stuff in Example4_Bob.ino. Bob's sketch is actually quite similar to Example3_Verify.ino, although he receives the message and signature on his RX1 pin.

language:c
// Delete this "blank" public key,
// copy/paste Alice's true unique public key from her terminal printout in Example4_Alice.

uint8_t AlicesPublicKey[64] = {
0xB4, 0x07, 0x88, 0x28, 0x8C, 0xFA, 0x71, 0xBA, 0x08, 0xE3, 0x38, 0xE0, 0x4A, 0x17, 0x68, 0xCC, 
0x3E, 0xCD, 0x48, 0xA8, 0x11, 0x52, 0xDD, 0x37, 0xA1, 0xC2, 0x55, 0x75, 0x81, 0xBE, 0x4E, 0x7E, 
0x78, 0x98, 0x95, 0xF6, 0x6D, 0xE7, 0x1C, 0x9A, 0x36, 0xE6, 0xB0, 0x14, 0x5D, 0x50, 0x67, 0x91, 
0x7C, 0x41, 0xB8, 0x99, 0x20, 0x75, 0x3A, 0x7D, 0xA1, 0xFB, 0xF5, 0x5E, 0x8A, 0x65, 0xF5, 0x8A
};

At the top, you need to copy in Alice's public key. Bob will need this to verify any messages and signatures he receives. Note, yours will be different than what I'm showing above.

language:c
void loop()
{
  if (Serial1.available() > 0) // listen on Serial1
  {
    // check for start header
    byte input = Serial1.read();
    //Serial.print(input, HEX);
    if (input == '$') headerCount++;
    if (headerCount == 3)
    {
      delay(100); // wait for entire message to come into Serial1 buffer (96 bytes at 9600 baud).

      headerCount = 0; // reset
      Serial.println("Message Received!");
      Serial.println();

      for (int bytes = 0 ; bytes < 32 ; bytes++) message[bytes] = Serial1.read();

      for (int bytes = 0 ; bytes < 64 ; bytes++) signature[bytes] = Serial1.read();

      printMessage();

      printSignature();

      // Let's verirfy!
      if (atecc.verifySignature(message, signature, AlicesPublicKey)) Serial.println("Success! Signature Verified.");
      else Serial.println("Verification failure.");
    }
  }
}

Above, we have Bob's entire loop(). He is listening for incoming data on his RX1 pin. If he hears the expected $$$, then he starts reading in the message and the signature, storing them in variables for later use.

Then Bob uses the atecc.verifySignature() function to see if everything is authentic. Note his third argument to this function - he is using AlicesPublicKey!

Example 5: Random

This example shows how to use the Random Number Generator on the Sparkfun Cryptographic Co-processor. It will print random numbers once a second on the serial terminal at 115200.

This example only requires 1 Artemis and 1 co-processor. If you just completed example 4, you can choose to use Alice or Bob. This example helps set the stage for Example 6, so it's a good idea to check it out and see how the ATECC508A does random numbers - particularly its ability to create 32 bytes of random data!

Note, this chip is a bit more capable than the built-in Arduino function random().

• random(max)
• random(min, max)

It has a basic random(min, max). This will return a random number of type long. Note, it works very similarly to the built-in Arduino random() function, you can send it a single argument as a max, or you can send it two (as min and max).

It also has the following 3 other functions that can be useful in other applications.

• getRandomByte()
• getRandomInt()
• getRandomLong()

Each of these functions return a random number of the type written into the name.

And lastly...

• updateRandom32Bytes() will create 32 bytes of random data and store it in atecc.random32Bytes[].

After calling updateRandom32Bytes() then your random 32 bytes of data are available at a public variable within the library instance. If your instance was named atecc as in the SparkFun examples, this array would be atecc.random32Bytes[]. This can be useful as a challenge or time-to-live-token (aka NONCE) to send to another device.

Example 6: Challenge

This example shows how to setup a "challenge and response" for authentication between two systems. This is one way to add more security to your communication channel. More specifically, it prevents attackers from intercepting a message and sending it at a later time. This doesn't seem like such a bad thing, but timing of a message is sometimes equally as important as the message itself. Once such interception attack was called the RollJam, and could be used to maliciously open garage doors and unlock cars. After completing this example, you will be able to defend your projects against this type of attack!

Hardware Hookup

For Example6_Challenge, you will need to setup two Artemis boards (each with their own co-processors) and connect a few jumper wires between Alice and Bob.

Connect the following pins like so:

Note, you're setup will also need to include a co-processor on each side connected via qwiic cables, and should look something like this:

Code Setup

Like Example 4, this also requires two unique sketches and setups. You will need to use both Example6_Challenge_Alice.ino and Example6_Challenge_Bob.ino.

Again, you will need to copy Alice's public key from her serial terminal, and then paste it into the top of Bob's sketch. Then upload Bob's sketch and watch both terminals.

For any new authentication cycle, Alice will initiate. User must reset Alice and send a "y" over serial at 115200. Bob will create a new random array of 32 bytes (this will be called a token - aka NONCE). It is also known as a "time-to-live token", because it will become invalid after a set amount of time. Bob sends the token to Alice. Alice will sign the token using her private ECC key, then send the signature to Bob. Bob will use the token, the signature, and Alice's Public Key to verify everything.

By creating a new random token, Bob now has the ability to control how long he thinks that token should be valid. This means that if an attacker intercepted the message, and they tried to send it later, it would no longer be valid.

Bob will also invalidate the token after a set amount of time. For our example it will be 150ms. This prevents any attacker from intercepting the message, and hanging on to it for later use. So if Alice doesn't respond within the set window of time (150ms), then Bob will clear out the token, and Alice must ask for another.

Because the token is unique every time, that means that Alice's signature will be unique every time. This prevents an attacker from trying to impersonate Alice by recording communications, and then later sending one.

Troubleshooting

For extra guidance, checkout the product video, which also includes the examples, laid out in this tutorial.

Resources and Going Further

Now that you've sent signed message between two systems, you are ready to integrate some security into your projects! In these examples we have used hard-wired serial messages between two Arduinos. That communication channel could be anything: Bluetooth, RFM69s, Wifi and the internet, you name it! Good luck!

• Schematic (PDF)
• Eagle Files (ZIP)
• Github (Hardware)
• Github (Arduino Library)
• Microchip ATECC508A DataSheet (PDF)
• CryptoAuthLib - Microchip CryptoAuthentication Library (includes python support)
• Board Dimensions (PDF) or (PNG)
• Product Video

Additional Documentation on the Cryptographic Standards (linked from datasheet):

• SHA-256 Algorithm
• HMAC Algorithm
• Elliptic Curve Digital Signature Algorithm (ECDSA)
• Elliptic Curve Diffie-Hellman (ECDH) Key Agreement (Revision 2)
• Elliptic Curve Diffie-Hellman (ECDH) Key Agreement (Revision 2- Draft)
• Diversified Keys
• NIST CAVP certification of the RNG

Need inspiration? Check out some of the Qwiic or IoT related tutorials!