SNMPv3 UCD and router (CISCO)

Hi,
I have searched through the archive and still not clear on a couple of
issues. I am starting work on writing a client using UCD SNMP to query
CISCO router using SNMPv3 for info.
The problem is that a number of things are not clear to me and I was
hoping somebody would clarify these issues. 
The way I understand things the keys for authentication and privacy both
need to be set up on the router (they may be generated by the router not
sure), but they also need to be set in the code  to both
session.securityAuthKey and session.securityPrivKey could be assigned
keys that would be the same as on the router?
Or do these get generated based on the passphrases passed in to
generate_KU? but then how is CISCO router supposed to decrypt it?
However CISCO documentation suggests "The security keys used for
authenticating and encrypting SNMPv3 packets are generated as a function
of the authoritative SNMP engine's engine ID and user passwords."
 
DO I understand this correctly that UCD library will generate
msgAuthoritativeEngineID for me? So at the end of the day the only
things that I should care about as paramterst to UCD APIs are keys, and
user name as well as the target and things I am inquiring about?
Any information and help is greatly appreciated.