Wireless reprogramming in a Wireless Sensor Network (WSN) is the process of uploading a new code image or relevant commands to sensor nodes or changing the functionality of existing code. As a WSN is usually deployed in hostile environments, so for security reasons every code update must be authenticate to prevent an opponent from installing malicious code in the network. A Secure and Distributed Reprogramming Protocol (SDRP) is the first distributed reprogramming protocol for WSNs. SDRP is based on distributed reprogramming approach that allows multiple authorized network users to simultaneously and directly reprogram sensor nodes without involving the base station.