The demand for using wireless paradigms for performing various information and communication operations has been exploded. The opportunistic networks is a special type of delay tolerant networks proposed to operate in an emergency manner to facilitate mobile connectivity between the nodes when there is no connectivity. These emergencies are caused either by human-made or natural disasters. Opportunistic Networks depend on mobile phones and other mobile devices that carry wireless technology. This paper is an attempt to expand the opportunistic network through the authentication nodes. We propose an NTRU algorithm for node authentication in opportunistic networks .NTRU algorithm is an asymmetric post-quantum cryptosystem. This algorithm is unbreakable and robust compared to RSA and ECC cryptosystem.