[Help-gnutls] Question regarding TLS with PSK

[Frank Eberle]

Hello,

I've to write an application which requires a secured communication 
channel. To keep the user's effort minimal I want to use pre-shared keys 
for authentication.
Now my question: In my understanding when using PSK-DH the client is 
authenticated when connecting to the server, but is the server also 
authenticated against the client?
Or in other words: When an attacker replaces the server by his own 
implementation is the client able to recognize this? Or do I have to use 
a server certificate to achieve this.

Best regards

Frank