AS_REP question

[NetSteady]

I'm actually speaking about the enc-part of the Kerberos packet itself,
not in the ticket. Is this the part you were speaking of?

Our problem is that we're trying to validate the password for the user
when we receive the AS-REP packet, but for some reason, we cannot find
where to get the encryption key for the enc-part. We've read the RFCs
(many many times) and are still having issues finding this.

Suggestions?