CryptoCape Hookup Guide
This Tutorial is Retired!
This tutorial covers concepts or technologies that are no longer current. It's still here for you to read and enjoy, but may not be as useful as our newest tutorials.
jbdatko, 
CaseyTheRobot 
Elliptical Curve Generator
The ATECC108 performs the Elliptic Curve Digital Signature Algorithm (ECDSA) on the chip. This is an authentication chip, like the ATSHA204. The goal of an authentication device is to assert the integrity and identity of a communicating party. The ATECC108 uses asymmetric cryptography, which means there is a public and private key. In short, this allows you to distribute public keys and keep individual private keys secret. This is unlike the ATSHA204 where each device needs a copy of the same secret key.
Atmel AVR Library
While the datasheet is under a NDA, Atmel provides an AVR based library to interface with this chip.
Linux Driver
There is a Cryptotronix Linux driver, with examples, available on GitHub. This blog post walks through using the software and describes the current status.