@MLs
Signing is supported using both atsha204a and pure software. They are perfectly compatible so you can mix all you want.
What is important to understand is that if you use software based signing, if someone gets physical access to your node, they can dump eeprom and obtain your secret hmac key (PSK) and using that they can potentially compromise your node network.
The benefit of a atsha is that the key is securely stored and cannot be extracted from the chip. At least it is according to Atmel. So if you plan to put your node "outside" it is recommended to use atsha. On your gateway it is less important as you would typically have your gateway placed "securely". If you do not, then your network would be compromised as an attacker could tap in to the communication between gateway and controller, which is not secured.
This limitation is not accidental. Supporting security between gateway and controller mean a dependency which would limit the ability to support a wide range of controllers and is therefore undesirable. And personally I don't really see a usecase for it anyway as gateways generally are placed indoors and are hooked up to a LAN in one way or another.
