A method for securing the execution of a session with a data processor, such as a smart card, under the control of at least two entities, such as servers. Session numbers and session keys are transmitted to the entities. The session number and key are applied to an algorithm in the data processor and the respective entity to produce a result and signature. The results and the signatures are transmitted to the data processor. A session corresponding to the results from the data processor is executed when the signatures are identical to the results. In another embodiment, one of the entities receives a delegation of a third entity to authorize execution of the session.