Wireless sensor networks (WSN) are envisioned to consist of large numbers of minimum capacity devices operating in demanding real-world environments. These issues, together with the inherent problems of wireless communication, make security an especially difficult problem. Many WSN also need to operate under real-time constraints. We discuss three routing protocols for WSN that have good real-time performance properties: SPEED, RAP and IGF. We suggest extensions to these protocols that improve their security properties. Denial of service is another key problem facing WSN. We discuss a highly decentralized algorithm for the detection and mapping of jammed regions of a WSN. The solution is robust to failures and can operate on partial information (a type of anytime algorithm). We conclude by considering several potential future directions for security solutions, including: secure groups based on relaxed semantics, exploiting physical properties, exploiting time validity intervals for data, and the interaction between security and privacy.