Secrecy-preserving refinement

Abstract

A useful paradigm of system development is that of step-wise refinement. In contrast to other system properties, many security properties proposed in the literature are not preserved under refinement (refinement paradox). We present work towards a framework for stepwise development of secure systems by showing a notion of secrecy (that follows a standard approach) to be preserved by standard refinement operators in the specification framework Focus (extended with cryptographic primitives). We also give a rely/guarantee version of the secrecy property and show preservation by refinement. We use the secrecy property to uncover a previously unpublished flaw in a proposed variant of TLS, propose a correction and prove it secure. We give an abstract specification of a secure channel satisfying secrecy and refine it to a more concrete specification that by the preservation result thus also satisfies secrecy. © Springer-Verlag Berlin Heidelberg 2001.