The fact that Apple could in the future modify their system to permit them to read iMessages (e.g. by interposing themselves between sender and receiver using f

The fact that Apple could in the future modify their system to permit them to read iMessages (e.g. by interposing themselves between sender and receiver using fake public keys) is not really a fair basis for alleging that Tim Cook or anyone else is telling "half-truths" in respect of what Apple is currently doing. He has said they are not reading them and that, at present, they cannot read them. I'm not aware of any basis for impugning his credibility in that respect. But it remains the case that anyone seriously concerned about security should continue to guard against that possibility in the future.