It’s not a secret. It’s on their website. Note: the Open Technology Fund is the CIA. Just like Radio Free Asia (or Radio Free X, they’re all CIA-run appendages of the US state department) which the fund grew out of. The US government very often funds technologies and startups that have the potential surveillance applications (among other things) and Signal was one of them. The people calling this a conspiracy theory have no idea what they are talking about, but that’s not uncommon when it comes to Americans and swallowing their own propaganda whole.