Personalization sketch for ATSHA204

This sketch is used to personalize the ATSHA204 crypto
circuit.
This is required in order to use the device for secure
communication.

The sketch also supports random key generation.

To personalize a ATSHA204 device, do the following:
1. Ensure the correct pin is used for the ATSHA204.
2. Execute the sketch without other changes to verify
   that it can communicate properly with the device.
3g. For a device used in a gateway:
    Enable LOCK_CONFIGURATION to lock the configuration
    and enable random key generation as well as key storage.
4g. Execute the sketch to lock the configuration and obtain
    a unique key. Be sure to note down the key printed in the
    UART log as it has been stored in the chip and will never
    be accessible again (a new key is calculated on subsequent
    runs).
    The key can still be changed.
5g. Enable SKIP_KEY_STORAGE to prevent generating new random
    keys on sketch re-execution.
3n. For a device used as a node:
    Enable USER_KEY_DATA and enter your private key data
    in user_key_data.
    Then enable LOCK_CONFIGURATION to lock the configuration
4n. Execute the sketch to lock the configuration and store
    the user-supplied key.
5n. Optionally: Enable SKIP_KEY_STORAGE to prevent re-writing
    the user supplied key on sketch re-execution.
6.  Optionally: Enable LOCK_DATA to prevent the key to be
    changed.

Author: fallberg