[embolism]

No modern computer can be constructed by an individual without trusting a corporation not to have coopted some part of the system. Therefore no communication system can exist that meets your criteria. (E.g. Because the CPU could be compromised)

Your argument is the equivalent of 'we can't trust any corporation'. It's a coherent position to take but it is extreme and doesn't lead to meaningful discussions about what is possible.

[jmillikin]

  > Therefore no communication system can exist that meets
  > your criteria. (E.g. Because the CPU could be compromised)

For the purposes of this discussion it's reasonable to assume that consumer hardware does not contain backdoors, because such extensive compromise of the computing infrastructure would require conspiracy on a massive scale (approximately every electronics manufacturer in the world).

[embolism]

Then you haven't explained how Apple could join another device to the encryption session without the user's password.