5 ms·

What happens if NSA starts operating a number of Tor exit nodes and eavesdropping on the outgoing traffic? What prevents them from doing so?

mitchty 13y ago
They start capturing lots of data. And nothing prevents them from doing so.
- noerps 13y ago
  They are donating bandwidth, which is always scarce.
doomrobo 13y ago
Nothing, but they would still not know where the traffic is coming from. The "Onion" defined in the Tor protocol is unwrapped layer by layer by each node. So the NSA has a choice where no option would help them too much: 1. Be the first node you access and be able to see your IP but not your traffic 2. Be the last node and be able to see your traffic but not your IP 3. Be a middle node and see neither
- sdfjkl 13y ago
  Can't they do both 1 and 2 and correlate the information?
  - dllthomas 13y ago
    Yes. Which is why we need to keep a lot of nodes running, and part of why Tor hidden services are a good thing.
  - doomrobo 13y ago
    I don't believe that's possible. If they have two nodes then they're still not a part of a defined path. For instance, someone can go through their entrance node and come out someone else's exit node and vice-versa. The NSA would have no idea who is going through where and shouldn't be able to correlate the data.
- marvin 13y ago
  What happens if you are logged into one of the services where the NSA has "direct access to the servers"?
  - dllthomas 13y ago
    That's covered in the diagram.
theboss 13y ago
Security professionals have hypothesized many attacks against the anonymity of the tor onion and what you describe is pretty close to one of them. If the NSA was to create tons Tor nodes (enter, exit, and relay), the onion may be broken. Tor is by no means perfect. It is only obfuscating. It is easy to see how this is broken if you click the TOR button on this thing and then imagine the TOR nodes say NSA on them. I think it is more fun to imagine security this way (extremely challenging and like you are protecting yourself from the perfect attacker, and the NSA is a good face to put on the perfect attacker). People don't realize how much trust they are putting in their hosting provider, cell carrier, etc.etc. It's insane.
- derrida 13y ago
  Run a node to stop this attack working!
- stephen_g 13y ago
  There isn't really such category as a tor 'enter' node. Any node can be the first node of the chain, but it has no idea whether it is the first or one in the middle of the chain. Essentially, it's as if the 'entrance node' is running on your computer. That means that no node knows the source of the traffic, and only the exit node knows the destination. For the NSA to effectively monitor Tor, they'd need to run a large proportion of the nodes - one paper thought it would require an attacker to run at least one third of the network.
  - theboss 13y ago
    Yes but one third is doable for a perfect attacker with 'unlimited resources'. It would be really interesting to determine how much this would cost
  - deadairspace 13y ago
    Do you have a link to said paper by any chance?
  - dweinus 13y ago
    If the NSA has the logs of ISPs that carry one third of the world's traffic, couldn't they execute the attack without running any Tor nodes? Or am I misunderstanding the onion protocol?
ams6110 13y ago
Frankly, I think you have to assume that the NSA is already doing this. I also think you have to assume they have the private keys for every major CA in the world.
- farmdawgnation 13y ago
  Worth noting: Having the private keys for all the CA's in the world just means that they could launch a man-in-the-middle attack against a secure service. (Which would be easy for a rudimentary traceroute to detect.) Not that they could decrypt SSL traffic talking directly to my server, for example. The susceptibility to this kind of attack is a big part of the knock that a lot of people have against HTTPS. It's generally been ignored as "too hard to pull off" - but it's also generally been assumed that your own government won't bother recording your communications without probable cause. Anyway, unless they were targeting a specific service (which they usually aren't, they usually target a person) it would require too much effort to set this up for all the secure services they use.

mitchty 13y ago

They start capturing lots of data. And nothing prevents them from doing so.

noerps 13y ago
They are donating bandwidth, which is always scarce.

doomrobo 13y ago

Nothing, but they would still not know where the traffic is coming from. The "Onion" defined in the Tor protocol is unwrapped layer by layer by each node. So the NSA has a choice where no option would help them too much: 1. Be the first node you access and be able to see your IP but not your traffic 2. Be the last node and be able to see your traffic but not your IP 3. Be a middle node and see neither

sdfjkl 13y ago
Can't they do both 1 and 2 and correlate the information?
- dllthomas 13y ago
  Yes. Which is why we need to keep a lot of nodes running, and part of why Tor hidden services are a good thing.
- doomrobo 13y ago
  I don't believe that's possible. If they have two nodes then they're still not a part of a defined path. For instance, someone can go through their entrance node and come out someone else's exit node and vice-versa. The NSA would have no idea who is going through where and shouldn't be able to correlate the data.
marvin 13y ago
What happens if you are logged into one of the services where the NSA has "direct access to the servers"?
- dllthomas 13y ago
  That's covered in the diagram.

theboss 13y ago

Security professionals have hypothesized many attacks against the anonymity of the tor onion and what you describe is pretty close to one of them. If the NSA was to create tons Tor nodes (enter, exit, and relay), the onion may be broken. Tor is by no means perfect. It is only obfuscating. It is easy to see how this is broken if you click the TOR button on this thing and then imagine the TOR nodes say NSA on them. I think it is more fun to imagine security this way (extremely challenging and like you are protecting yourself from the perfect attacker, and the NSA is a good face to put on the perfect attacker). People don't realize how much trust they are putting in their hosting provider, cell carrier, etc.etc. It's insane.

derrida 13y ago
Run a node to stop this attack working!
stephen_g 13y ago
There isn't really such category as a tor 'enter' node. Any node can be the first node of the chain, but it has no idea whether it is the first or one in the middle of the chain. Essentially, it's as if the 'entrance node' is running on your computer. That means that no node knows the source of the traffic, and only the exit node knows the destination. For the NSA to effectively monitor Tor, they'd need to run a large proportion of the nodes - one paper thought it would require an attacker to run at least one third of the network.
- theboss 13y ago
  Yes but one third is doable for a perfect attacker with 'unlimited resources'. It would be really interesting to determine how much this would cost
- deadairspace 13y ago
  Do you have a link to said paper by any chance?
- dweinus 13y ago
  If the NSA has the logs of ISPs that carry one third of the world's traffic, couldn't they execute the attack without running any Tor nodes? Or am I misunderstanding the onion protocol?

ams6110 13y ago

Frankly, I think you have to assume that the NSA is already doing this. I also think you have to assume they have the private keys for every major CA in the world.

farmdawgnation 13y ago
Worth noting: Having the private keys for all the CA's in the world just means that they could launch a man-in-the-middle attack against a secure service. (Which would be easy for a rudimentary traceroute to detect.) Not that they could decrypt SSL traffic talking directly to my server, for example. The susceptibility to this kind of attack is a big part of the knock that a lot of people have against HTTPS. It's generally been ignored as "too hard to pull off" - but it's also generally been assumed that your own government won't bother recording your communications without probable cause. Anyway, unless they were targeting a specific service (which they usually aren't, they usually target a person) it would require too much effort to set this up for all the secure services they use.