Impossible! If the Iranians knew that we were reading their mail, they would never let us know that they knew. They would continue to use the codes, but instead of sending accurate messages they would use those channels for disinformation against us.How clever! The only problem: Disinformation campaigns of this sort are difficult to pull off and hence, extremely rare. Two Cold War examples come to mind. After the Russians discovered our infamous spy tunnel in Berlin, they continued to carry on normal communications for several months. Likewise, when the US discovered that the Moscow Embassy had been bugged in the 1980s, Secretary of State George Shultz decided simply to conduct business as usual rather than carry out a disinformation campaign.