whenever I discuss Tor with people who have just enough knowledge to be dangerous, I hear "yea, but it was funded by the US so it probably has a backdoor/wouldn't be funded if they couldn't read the data".
I don't agree with that, but what can you say other than "it's open source so many eyeballs are auditing it"?
Besides that, I use to say that I would not put a backdoor in the system used by my spies to communicate. It would be really dangerous for me if it fallen in the wrong hands.
Any backdoor in TOR that could remain hidden for so long would have to be a protocol flaw. Implementation changes too much to rely on an obfuscated 'bug' and anything as straightforward as your suggestion would simply be found and removed immediately.
Protocol flaws can of course be found and used by anyone.
I am no expert, but I thought the weakness of tor was that a goverment could control many of the exit nodes (combied with timing attacks to find the user?), since most users don't want to run them for fear of being arrested for whatever the users were doing on the network?
I don't agree with that, but what can you say other than "it's open source so many eyeballs are auditing it"?