We present SADSR (security-aware adaptive DSR), a secure routing protocol for mobile ad hoc networks. SADSR authenticates the routing protocol messages using digital signatures based on asymmetric cryptography. The basic idea behind SADSR is to have multiple routes to each destination and store a local trust value for each node in the network. A trust value is assigned to each path based on trust values of the nodes which occur on that path. The paths with higher trust values are preferred for routing. We implemented our approach in ns2 simulator and compared the performance of SADSR and DSR. Our results show that in the presence of malicious nodes SADSR outperforms DSR in packet delivery ratio with an acceptable network load.