The API key is an symmetric key, described & generated here:
http://yubico.com/developers/api/
shared secretly on your client SDK side and on Yubico validation server side. So when you receive an OTP validation response from Yubico validation server. So you will be able to verify the "signature" to make
sure it is a legit response.
You can see from the PHP client example in:
http://code.google.com/p/php-yubico/sou ... Yubico.php
But the signature is optional, though we recommend production deployments to use it & check it.
> Can this remote authentication script verify any Yubikey?
The Yubico validation server will verify OTP from any Yubikey. But if you are NOT the issuer of that key, you don't have the API key to verify the signature. You can only validate the OTP is OK or not.
If you are opt for the details, the src of the validation server is at:
http://yubico.com/developers/srv/
Say if you issue 500 keys to your users, all of them can be associated under your client ID so you can verify their validation responses from Yubico.
Paul
