brucker.ea:verification:2005 ArticleInAPeriodical Heidelberg Springer-Verlag 2005 International Journal on Software Tools for Technology (STTT) 7 3 233-247 BruckerAchimD WolffBurkhart A Verification Approach for Applied System Security We present a method for the security analysis of realistic models over off-the-shelf systems and their configuration by formal, machine-checked proofs. The presentation follows a large case study based on a formal security analysis of a CVS-Server architecture. The analysis is based on an abstract architecture (enforcing a role-based access control), which is refined to an implementation architecture (based on the usual discretionary access control provided by the \posix environment). Both architectures serve as a skeleton to formulate access control and confidentiality properties. Both the abstract and the implementation architecture are specified in the language Z. Based on a logical embedding of Z into Isabelle/HOL, we provide formal, machine-checked proofs for consistency properties of the specification, for the correctness of the refinement, and for security properties.