Due to node mobility, the ad hoc network topology is dynamical so that on-demand routing protocols are more fit than other routing protocols. Most secure on-demand routing protocols are designed that the destination or source is able to detect the attacks on routing paths after accepting routing requests or routing replies. In this paper, we present a secure on-demand source routing protocol without the assumption of a specific cryptographic system provides per-hop broadcast authentication in routing discovery phase and security in communication phase and takes effect on our trust-based ad hoc environment. Our hop by hop broadcast authentication provides forwarding routing packets with their trust levels for abstaining from unreliable or malicious nodes. Through security analysis and discussion, we characterize our mechanism and show that it is effectively and efficiently.