Security is one of the main issues of modern computer science. Nowadays more and more people use a computer to perform sensitive operations like bank transfer, Internet shopping, tax payment or even to vote. Most of these users do not have any clue how the security is achieved, therefore they totally trust their applications. These applications often use cryptographic protocols which are notoriously error prone even for experts. For instance a flaw was found in the Needham-Schroeder protocol seventeen years after its publication. These errors come from several aspects: Proofs ofsecurity of cryptographic primitives can contain some flaws. Security properties are not well specified, making it difficult to formally prove them. Assumptions on the intruder's model might be too restrictive. In this habilitation thesis we propose formal methods for verifying security of these three layers. First, we build Hoare logics for proving the security of cryptographic schemes like public encryption, encryption modes, Message Authentication Codes (MACs). We also study electronic voting protocols and wireless sensor networks (WSNs). In each one of these areas we first analyze the required security properties in order to propose a formal model. Then we develop adequate techniques for their verification.
