Verification techniques have been applied to the design of secure protocols for decades. However, relatively few efforts have been made to ensure that verified designs are also implemented securely. Static code verification techniques offer one way to bridge the verification gap between design and implementation, but require substantial expertise and manual labor to realize in practice. In this short paper, we propose black-box runtime verification as an alternative approach to extend the security guarantees of protocol designs to their implementations. Instead of instrumenting the complete protocol implementation, our approach only requires instrumenting common cryptographic libraries and network interfaces with a runtime monitor that is automatically synthesized from the protocol specification. This lightweight technique allows the effort for instrumentation to be shared among different protocols and ensures security with presumably minimal performance overhead.