  We propose a new simple \emph{trace} logic that can be used to specify
\emph{local security properties}, i.e. security properties that refer to a
single participant of the protocol specification. Our technique allows a
protocol designer to provide a formal specification of the desired security
properties, and integrate it naturally into the design process of cryptographic
protocols. Furthermore, the logic can be used for formal verification. We
illustrate the utility of our technique by exposing new attacks on the well
studied protocol TMN.
