Wireless Sensor Networks (WSNs) are being used for many applications ranging from mobile target surveillance to intelligent home networking. The data transmitted by those applications are sensitive. Then due to the weakness of the radio links, appropriate protection mechanisms are needed to prevent attackers from exploiting those lacks of security. In this paper we present a solution to authenticate the nodes and protect the sent data. We investigate the use of secure tunnels as a solution to improve the protection of WSNs. We propose a tunneling scheme that conforms to the security requirements of WSNs while having less computational and network overhead. A set of experiments has been conducted to assess the performance of the proposed scheme with regard to traditional tunnels built using the IPSec protocol. We found that our protocol considerably reduces the number of transmitted messages as well as the computational load, which makes it suitable for WSNs.