  We propose a methodology for verifying security properties of network
protocols at design level. It can be separated in two main parts: context and
requirements analysis and informal verification; and formal representation and
procedural verification. It is an iterative process where the early steps are
simpler than the last ones. Therefore, the effort required for detecting flaws
is proportional to the complexity of the associated attack. Thus, we avoid
wasting valuable resources for simple flaws that can be detected early in the
verification process. In order to illustrate the advantages provided by our
methodology, we also analyze three real protocols.

Cryptography and Security