Groups of prime order

[Joanna Orzechowska]

Hi CP's!

Hope someone would be so kind to help me wiht this:

Is it weaker to use arithmetic mod (p-1), and hence all Zp, when 
suggested to work in a group of prime order q?

This question is connected with discrete log signature protocols such 
as that in Pedersen's "Improved privacy in Wallets with Observers" or 
Schnorr's.

I would appreciate any help ASAP, since I'm in a hurry.
Please, answer me by personal mail since I'm not subscribed to the 
CPs list now.

Thanks and best wishes from Poland.

            Joanna