Abstract : Cryptographic protocols are small concurrent programs designed to guarantee the security of exchanges between participants using non secure medium. Establishing the correctness of these protocols is crucial. Unfortunately, the existence of cryptographic primitives such as encryption is not sufficient to ensure security. The security of exchanges is ensured by cryptographic protocols which are notoriously error prone. To verify such protocols, a line of research consists in considering encryption as a black box and assuming that an adversary can't learn anything from an encrypted message except if he has the key. This is called the perfect cryptography assumption. In this thesis, we relax the perfect cryptography assumption by taking into account some algebraic properties of cryptographic primitives. We give decision procedures for the security problem in presence of several algebraic operators.