To achieve the security requirements we established in Section 3 we have designed and implemented two security building blocks: SNEPand TESLA. SNEPprovides data confidentiality, two-party data authentication, integrity, and freshness. TESLAprovides authentication for data broadcast. We bootstrap the security for both mechanisms with a shared secret key between each node and the base station (see Section 2). We demonstrate in Section 8 how we can extend the trust to node-to-node interactions from the node-to-base-station trust.