Security protocols are short programs aiming at securing
communications over a network. They are widely used in our everyday
life. Their verification using symbolic models has shown its interest
for detecting attacks and proving security properties. In particular,
several automatic tools have been developed and are used to
efficiently detect flaws. In this talk, we will first review results
and techniques that allow automatic analysis of security protocols.
In a second part, we will present recent results that demonstrate that
formal abstract models used for verification are actually sound with
respect to much richer models that considers issues of complexity and
probability. As a consequence, it is possible to derive strong, clear
security guarantees still keeping the simplicity of reasoning in
symbolic models.