In this work, we use our proposed UML-based HW/SW co-design platform (UCoP) to implement a reconfigurable cryptographic system for network multimedia applications. The UCoP is categorized into three reusable models, including software application, hardware configuration and system management models. Through the use of the reusable models, the proposed dynamically partially reconfigurable system can be easily implemented in UCoP. Furthermore, the direct interaction with the real system architecture in UCoP is very helpful to designers in validating and analyzing system correctness and performance at a high-level, which can significantly reduce system development efforts. We compare the use of UCoP with a lower-bound estimation method by implementing a network multimedia application with the data encryption/decryption. According to our experiment results, we can clearly see how UCoP plays a key role in helping designers to develop dynamically partially reconfigurable systems with hard real-time constraints.