Method and means for modifying gases or fumes fed through a filter, from its inlet side to its outlet side, submitted to an electric plasma having its maximum plasma density at the filter’s inlet side. The method comprises the first and the second party agreeing on a pseudo random mapping depending on a shared key k, Fk, mapping at least x to y, and the first party modifying the messages by replacing x by y in each message M, D). This aspect of the method allows the user to control the drive state transition and inject errors on the inbound and outbound drive traffics.