Developing Security Protocols by Refinement Sample Clauses

Developing Security Protocols by Refinement. We propose a development method for security protocols based on stepwise refinement. Our four-level refinement strategy guides the transformation of abstract security goals (Level 0) into protocols that are secure when operat- ing over an insecure channel controlled by a Dolev-Yao-style intruder (Level 3). The intermediate refinement steps successively introduce local states (Level 1), communication channels with security properties and an intruder (Level 2), and cryptographic operations realising these channels (Level 3). The abstractions used provide insights on how the protocols work and xxxxxx the development of entire families of protocols sharing a common structure and properties. In contrast to post-hoc verification methods, protocols are developed together with their correctness proofs. We have implemented our method in Isabelle/HOL and used it to develop several entity authentication and key transport protocols. We can report on progress on all fronts: we have improved our refinement strategy and protocol modelling technique, we have extended existing and added new case studies covering additional protocol features, and we have extended our theory of refinement. Regarding the refinement strategy, we have defined simpler and more general initial models for the security goals. In particular, we have defined abstract protocol-independent initial models for secrecy as well as for weak and strong authentication. We have developed a more concise representation of the intruder events that fake messages on the channels at later levels, allowing the refinement of the intruder to rely on lemmas of a standard, recurring form. We have extended the case studies of server-based key transport to cover a range of classical protocols all derived form a common Level 1 model. These include Xxxxx-Xxxxxxx’x version of Otway-Rees, Yahalom, Xxxxxxx-Xxxxxxxxx, Xxxxxxx-Xxxxx and Kerberos IV and V (the last two in progress). Finally, we have extended our theory of refinement with a notion of obser- vation (cf. [Abr10]). This allows us to prove theorems about the soundness of refinement as a method to establish the inclusion of observable traces and the preservation of already established properties by subsequent refinements. In our view, these properties are indispensable for a clear semantics of the refinement process. More details about this work can be found in [SB09].
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