Mobile devices with wireless network capabilities can be associated to form ad hoc networks to share resources; however, such an association of devices requires authentication. At present, PIN is the common authentication method, but in many cases, small devices may not have input interfaces to accommodate PIN entry. We therefore design a gesture-based authentication scheme, called GesturePIN, for associating multiple mobile devices; our solution provides the advantage of being adaptable to any PIN authentication systems. We have also conducted a quantitative user study to understand the speed and accuracy of people using our gesture-based system compared to using PIN.