A useful paradigm of system development is that of stepwise 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 We use the secrecy property to uncover a previously unpublished flaw in a proposed variant of TLS, propose a correction and prove it secure.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.