As much as I love Tor -- or at least, find it useful -- that's a horrible misconception.
You're trusting a bunch of stuff, in using Tor. There's no way to know what share of relays are malicious. Or how many undisclosed vulnerabilities are in active use. Or whether at least some Tor Project staff are failing to disclose malicious relays and vulnerabilities.
You just don't know.
That doesn't mean you avoid using Tor. Because, in theory, there are no better options. But it does mean that you use it carefully.
For example, always hit an entry guard through at least a VPN. Better, through nested VPN chains. And use firewall rules to prevent leaks. Not just Tor browser in Windows.
I suppose you are correct, Tor is not 100% trust free. But with a VPN, all trust is placed in a single party. With Tor, trust is divided between nodes - connecting to a single malicious node won't hurt you. You don't have to trust the software either, since you can read the source code to ensure trust is divided properly. But even with an open-source VPN client, you have to trust the server.
> Always hit an entry guard through at least a VPN.
That's a horrible misconception. There is no added benefit to using Tor over a VPN. It only worsens the risk - you're essentially creating a permanent entry node with a money trail.
Well, there are normally seven hops for that, not just three. So malicious relays are less problematic.
But then there's the risk from undisclosed vulnerabilities. In early 2014, CMU researchers deanonymized an unknown number of Tor users and onion sites using the "relay early" bug. The bug allowed relays to communicate covertly in the process of circuit establishment. So malicious relays run by CMU could identify each other, and cooperate to deanonymize circuits.
And then the FBI subpoenaed all their data. It took over at least one onion site (Playpen) and then pushed its NIT malware to perhaps hundreds of users. Who were then arrested and prosecuted.
So when did the Tor Project learn about the "relay early" bug? They claim that they didn't know, and didn't notice the suspicious relay activity, until after the CMU people went public. But how do we know? Indeed, from what I've seen of the FoIA production about the Tor Project, I'm not so confident that they don't cooperate with the FBI etc.
As far as I know, even when you use hidden services it is enough for the 1st and the 3rd to be malicious in order to de-anonymise a user. The tor security is barely enough (if it is enough at all) - there is no reason to believe that the FBI/FSB/etc don't have enough relays up in order to de-anonymise most users. I2P is much better in that regard.
Heck, until recently the tor team used 80-bit truncated sha-1, 1024-bit rsa, and 128-bit AES for their traffic, not to mention that the tor browser ships with javascript enabled by default.
In theory, I don't see how entry and exit are enough to deanonymize. They don't even know that they're in the same circuit unless they have a covert channel (like relay early) or manage traffic correlation during the ~10 minute circuit lifetime.
And then, using onion services, there are two three-relay circuits that meet at a rendezvous point. One picked by the onion, and the other by the user. So even deanonymizing one of those circuits would be insufficient.
But that's all theoretical. In practice, there are likely undisclosed vulnerabilities. Perhaps lots of them.
I do agree that the Tor browser standalone is rather a joke. Especially if it's in Windows. You at least want to be using Whonix. And if you really care, Whonix in Qubes.
> They don't even know that they're in the same circuit unless they have a covert channel (like relay early) or manage traffic correlation during the ~10 minute circuit lifetime.
No reason to think that they would not do that.
> And then, using onion services, there are two three-relay circuits that meet at a rendezvous point. One picked by the onion, and the other by the user. So even deanonymizing one of those circuits would be insufficient.
It would be sufficient to de-anonymise one of the parties.
> In practice, there are likely undisclosed vulnerabilities. Perhaps lots of them.
My point is that you do not need an undisclosed vulnerability to break tor if you have enough resources.
One major threat factor that Tor doesn't have a bulletproof solution to, and likely never will, is correlation attacks. It's been shown to be plausible that by observing the timing and size of packets, even without knowing the contents, is enough to determine that two relays are part of the same circuit.
Well, any system that relies on tunneling is vulnerable to correlation attacks. And drilling down by looking at traffic between autonomous systems. Unless it uses chaff to maintain constant throughput.
But will doing that be worth it to find someone like me? I doubt it. I'm just a hobbyist and writer.
You're trusting a bunch of stuff, in using Tor. There's no way to know what share of relays are malicious. Or how many undisclosed vulnerabilities are in active use. Or whether at least some Tor Project staff are failing to disclose malicious relays and vulnerabilities.
You just don't know.
That doesn't mean you avoid using Tor. Because, in theory, there are no better options. But it does mean that you use it carefully.
For example, always hit an entry guard through at least a VPN. Better, through nested VPN chains. And use firewall rules to prevent leaks. Not just Tor browser in Windows.