Using this definition of information flow security, a general security model for nondeterministic computer systems is presented. On one hand, our model is based on information flow which allows it to explicate security semantically as other information flow models. On the other hand, our model imposes concrete constraints on the internal system processes which facilitate implementation and verification in the fashion of access security models. Our model is also more general than previous state-based information flow models, e.g. allowing for concurrency among system processes, which is more suitable for distributed systems. Proving Properties of Security Protocols by Induction Lawrence C Paulson Informal justifications of security protocols involve arguing backwards that various events are impossible.
Inductive definitions can make such arguments rigorous.
There is no restriction to finite-state systems and the approach is not based on belief logics. Protocols are inductively defined as sets of traces, which may involve many interleaved protocol runs. Protocol descriptions model accidental key losses as well as attacks. The model spy can send spoof messages made up of components decrypted from previous traffic. Assertions concerning secrecy and authenticity have been proved.