Security of wireless sensor network (WSN) is always considered a critical issue and has a number of considerations that separate them from traditional wireless sensor network. First, sensor devices are typically vulnerable to physical compromise. Second, they have significant power and processing constraints. Third, the most critical security issue is protecting the aggregate output of the system, even if individual nodes may be compromised. While a variety of security techniques are being developed and lots of researches are going on security fields. In this paper we have proposed a new technique to provide data authentication and privacy in faster, scalable and cost effective way.