Inter device dependency and mutual cooperation of devices is a must in pervasive computing environment. This is to overcome the barriers posed by several shortcomings of pervasive environment including limited memory and computational capability, poor battery power etc. The knowledge of valid, authenticated devices is vital in this scenario to ensure security and privacy. At the same time we have to ensure that no malicious device is interacting with any other valid device. As an attempt to address this issue, we have modified the well known LPN (Learning Parity with Noise) based H-C (Human-Computer) [1-2] authentication protocol. In this paper, we have shown it to be feasible and realistic in the trusted device discovery mechanism of pervasive ad hoc network. Along with two separate models for both large and small networks, the paper presents several possible attack scenarios with their solutions.