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:

To create a digital signature we need:

To verify a digital signature we need:

1. Data

2. Private Key

3. Algorithm

1. Data

2. Signature

3. Public Key

4. Algorithm

Algorithm output: a new digital signature

Algorithm output: yes or no

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.

An example demonstrating the functionality of an asymmetric key pair (Alice and Bob).

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