We propose a framework for constructing secure systems at the architectural level. This framework is composed of an implementation-oriented formalization of a system?s architecture, which we call the formal implementation model, along with a method for the construction of a system based on elementary analysis, implementation, and synthesis steps. Using this framework, security vulnerabilities can be avoided by constraining the architecture of a system to those architectures that can be rigorously argued to implement all corresponding functional and security requirements, and no other. Furthermore, the framework enables the verification and validation of system correctness by enforcing traceability of final system components to their corresponding design, architecture, and requirement work products.