Method for defining a filtering module suitable for filtering information, according to a predetermined security policy, between a first module adapted for processing information with a first sensitivity level, and a second module adapted for processing information with a second sensitivity level distinct from the first sensitivity level, said first and second modules being connected, in parallel with the filtering module, by a cryptographic module suitable for applying cryptographic functions, the method being comprising the following steps: - a set of filtering rules is defined, translating the predetermined security policy, in a compilable language, said filtering rules defining the properties of the information whereof transmission is allowed by the filtering module between the first and second modules; - said predefined set of rules is compiled; - said compiled set of rules is integrated into a rules database of the filtering module said method being characterized in that: - validation processing for the predefined set of rules is carried out, validating that a transmission authorization or refusal has in fact been provided by applying said set of rules to any information that may be provided at the input of the filtering module; and in that - the set of filtering rules includes at least one protocol automaton, defined by a set of states corresponding to successive steps of the implementation of a communication protocol, and events causing transitions between said states, the set of filtering rules defining static, time and dynamic properties of the information authorized to be transmitted, the validation processing for the predefined set of rules further comprises a step for validating the coherence of the rules of said set of rules, the step for validating the coherence of the rules comprises detecting at least one anomaly from among: - the existence in the set of rules of first and second rules associated with different actions, the first rule being applied on all of the objects of the second; - the existence in the set of rules of two rules associated with different actions, and each of them is applied on a subset of the objects to which the other is applied; - the existence of two rules executing the same action on the same objects. - a set of filtering rules is defined, translating the predetermined security policy, in a compilable language, said filtering rules defining the properties of the information whereof transmission is allowed by the filtering module between the first and second modules; - said predefined set of rules is compiled; - said compiled set of rules is integrated into a rules database of the filtering module said method being characterized in that: - validation processing for the predefined set of rules is carried out, validating that a transmission authorization or refusal has in fact been provided by applying said set of rules to any information that may be provided at the input of the filtering module; and in that - the set of filtering rules includes at least one protocol automaton, defined by a set of states corresponding to successive steps of the implementation of a communication protocol, and events causing transitions between said states, the set of filtering rules defining static, time and dynamic properties of the information authorized to be transmitted, the validation processing for the predefined set of rules further comprises a step for validating the coherence of the rules of said set of rules, the step for validating the coherence of the rules comprises detecting at least one anomaly from among: - the existence in the set of rules of first and second rules associated with different actions, the first rule being applied on all of the objects of the second; - the existence in the set of rules of two rules associated with different actions, and each of them is applied on a subset of the objects to which the other is applied; - the existence of two rules executing the same action on the same objects. - the existence in the set of rules of first and second rules associated with different actions, the first rule being applied on all of the objects of the second; - the existence in the set of rules of two rules associated with different actions, and each of them is applied on a subset of the objects to which the other is applied; - the existence of two rules executing the same action on the same objects.