Isn’t Signal at least partially funded by the agency?
What part of non-profit and open-source do you not understand?
Review the source, build it yourself, be happy. It uses well-known assymetric encryption algorithms. Not much your agency could really do here even if they harvest all the traffic from the server.
Was my fucking question about the integrity of the algorithms they use, or was it about who’s been funding the product? Because a quick web search will show you that they did in fact fund it at one point.