7 ms·

Is Tor Safe? Think Again.

47 points by Aetius 16y ago

wmf 16y ago
From 2006/2007.
- AndrewS 16y ago
  Given the direction in which governments seem to be moving, it's probably more relevant now than it was then.
  - chunkybacon 16y ago
    Too paranoid to upvote and comment from my normal account...
  - eftpotrm 16y ago
    Speaking for the US and UK, I'd hardly call what we had in '06 particularly liberal. DHS in particular springs to mind...
shaddi 16y ago
Some good points here. A couple thoughts: - If, for some reason that I can't really conceive of, you wanted to connect to a far-away access point, you'd need a highly directional antenna (due to RF physics). Doing this actually makes direction finding extremely challenging, for the same reason you can't see a laser from the side (unless it's super high power and has something to reflect off of, which is unlikely to be the case in the wifi scenario). - End-to-end encryption plus an anonymization mechanism like Tor seems to me to be pretty impervious to attackers, assuming the implementation of your encryption and anonymization are both correct (which, admittedly, is a big if, but is not a /fundamental/ issue; you could envision a system engineered to be correct). If you have a secure, trust-worthy, out-of-band mechanism for exchanging keys with whoever you want to talk to, even if someone owns the infrastructure you're using they won't be able to decrypt your communication, or know who the source and destination are if you're using an anonymization mechanism. This also assumes you trust the person you're communicating with, etc. I'd love for someone to correct my understanding of this if I'm wrong.
- deleted 16y ago
  [deleted]
- wmf 16y ago
  If you first track down the location of the access point, then you know the directional antenna is pointed at you. From there, the direction finding is easy. I think a major part of the rant is that Tor isn't provably secure against yet-to-be-discovered attacks, and several attacks against Tor have been discovered (and fixed) over its history.
  - shaddi 16y ago
    Right, but the idea behind direction finding is that you can triangulate the position of the transmitter. If you just have a bearing you have to search over a large area -- these links could be many kilometers long. Not saying it's impossible, but using highly directional antennas makes direction finding much more difficult.
- ehsanul 16y ago
  I'm no security expert, but I don't think you even need an out-of-band key exchange mechanism. Just use public key cryptography [1], as used in SSH/TLS/PGP/GPG. [1] http://en.wikipedia.org/wiki/Public-key_cryptography http://en.wikipedia.org/wiki/Public-key_cryptography
  - deleted 16y ago
    [deleted]
  - DougBTX 16y ago
    I was about to write this response, but I see that it is more clearly written in the wikipedia article already: Another potential security vulnerability in using asymmetric keys is the possibility of a man-in-the-middle attack, in which communication of public keys is intercepted by a third party and modified to provide different public keys instead. Encrypted messages and responses must also be intercepted, decrypted and re-encrypted by the attacker using the correct public keys for different communication segments in all instances to avoid suspicion. This attack may seem to be difficult to implement in practice, but it's not impossible when using insecure media (e.g. public networks such as the Internet or wireless communications). A malicious staff member at Alice or Bob's ISP might find it quite easy to carry out. In the earlier postal analogy, Alice would have to have a way to make sure that the lock on the returned packet really belongs to Bob before she removes her lock and sends the packet back. Otherwise the lock could have been put on the packet by a corrupt postal worker pretending to be Bob to Alice. The workaround is to either exchange the public keys out of band, or distribute a certificate which can be used to verify public keys out of band.
sown 16y ago
So what about for hidden tor services?
- wmf 16y ago
  I think one of the points of the rant is that you have no way to know whether Tor is safe or not; if Tor is compromised then you might as well assume that it's completely compromised, including hidden services.
- x12x12x12 16y ago
  Assuming you trust that hidden service? I imagine if all the nodes between you and that service had gone rogue, it would be possible to positively identify that you (or the Tor client IP at the entry point) communicated with that service, at what time, and generally how much was sent back and forth.
x12x12x12 16y ago
Security can succeed by making an attack economically or logistically impractical. You have to consider when using any such system: 1. What would it cost the adversary to pull off a successful attack to reveal your identity? Would it be worth it to the attacker to do so? 2. Are there easier, more obvious targets? I would say it's a possible useful tool of increasing that cost for a potential adversary above their threshold of resources and motivation. If I'm wrong, tell me where I posted this from, and I'll go hide in the woods.
- corin_ 16y ago
  Naturally depends on who you're trying to hide from. This article seems to have been written from the point of view of "the CIA are watching me", not "I don't want someone to hack my facebook profile". And based on that logic, you have to assume that the CIA (or whatever agency) won't chose who to spy on based on who will cost them the least money.
  - pyre 16y ago
    The CIA won't choose to spend $1billion+ to spy on a single person unless they are really important.
    - wladimir 16y ago
      Most of the things he mentions are very cheap to pull off, though. Proxy honeypots, sniffing ISP internet connections, querying IPs, email surveillance -- the infrastructure is already in place they just have to type some commands. Cost: $0. On the other hand, actions that require actually sending men in suits and vans filled surveillance equipment can be costly. If they're doing that, you know you're in big trouble.
      - mootothemax 16y ago
        Most of the things he mentions are very cheap to pull off, though. Proxy honeypots, sniffing ISP internet connections, querying IPs, email surveillance -- the infrastructure is already in place they just have to type some commands. Cost: $0. I'm sorry but I have to jump in here - you're writing off an awful lost of resources under the banner of "they just have to type some commands."
jwhitlark 16y ago
When four people sit down to talk conspiracy, three are government agents, and the fourth is a fool.
ZoFreX 16y ago
Between the terrible grammar, grade school sentence structure, needless paranoia, senseless rambling and overall [citation needed]-ness of the article, I'm afraid I didn't really get the point. I thought it was going to explain why Tor is unsafe, yet it just made some broad speculative points and finished with a final jab in Tor's direction with no strength or conviction behind it.
iuguy 16y ago
I'll try to be careful with my words here (to avoid ambiguity more than anything else), but there are different programmes in different countries that provide different degrees of interception. In the UK we have the Regulation of Investigatory Powers Act 2000, which amongst other things forces service providers to keep logs of Internet activity for the police. These logs are typically of the order of IP address and connection type, not the actual data itself. This applies to pretty much all Internet access coming out of the UK somewhere along the line. Beyond the police there are means of intercepting specific Internet traffic. It's easier for me to talk about US interception capabilities at that level though (as it's more publicised). The FBI, NSA, CIA and (if IIRC but they might be colluding with another agency) the DHS all have their own independent capabilities for broad sweeps and targeted surveillance. These capabilities are exercised according to remit. The agencies have information sharing agreements with each other, and the relevant agencies have international sharing agreements with their counterparts e.g. UKUSA intelligence sharing agreements etc. If you want anonymity, you have to understand what you're trying to protect yourself from and (if possible) your adversary's capabilities. Having worked in countries with significant local interception capabilities that I do want to protect against, usually a properly configured VPN or SSH tunnel to a safe country is about as good as you're going to get without getting into government crypto (and if you're using government crypto in a hostile environment like that you're probably breaching some rule somewhere anyway). As to the question of whether or not Tor is safe, I assumed it was public knowledge that various countries' intelligence services ran monitored exit nodes for quite a while. I've seen malicious Tor exit nodes in investigations and have known people who've set them up for the express purpose of monitoring them.
unicornporn 16y ago
Not that the post actually brought up the Tor concept, but... I hate it when people diss the Tor concept by making the assumption that all uses of Tor requires an exit point. It doesn't. See torchat as an example. https://code.google.com/p/torchat/ https://code.google.com/p/torchat/

47 points by Aetius 16y ago

wmf 16y ago

From 2006/2007.

AndrewS 16y ago
Given the direction in which governments seem to be moving, it's probably more relevant now than it was then.
- chunkybacon 16y ago
  Too paranoid to upvote and comment from my normal account...
- eftpotrm 16y ago
  Speaking for the US and UK, I'd hardly call what we had in '06 particularly liberal. DHS in particular springs to mind...

shaddi 16y ago

Some good points here. A couple thoughts: - If, for some reason that I can't really conceive of, you wanted to connect to a far-away access point, you'd need a highly directional antenna (due to RF physics). Doing this actually makes direction finding extremely challenging, for the same reason you can't see a laser from the side (unless it's super high power and has something to reflect off of, which is unlikely to be the case in the wifi scenario). - End-to-end encryption plus an anonymization mechanism like Tor seems to me to be pretty impervious to attackers, assuming the implementation of your encryption and anonymization are both correct (which, admittedly, is a big if, but is not a /fundamental/ issue; you could envision a system engineered to be correct). If you have a secure, trust-worthy, out-of-band mechanism for exchanging keys with whoever you want to talk to, even if someone owns the infrastructure you're using they won't be able to decrypt your communication, or know who the source and destination are if you're using an anonymization mechanism. This also assumes you trust the person you're communicating with, etc. I'd love for someone to correct my understanding of this if I'm wrong.

deleted 16y ago
[deleted]
wmf 16y ago
If you first track down the location of the access point, then you know the directional antenna is pointed at you. From there, the direction finding is easy. I think a major part of the rant is that Tor isn't provably secure against yet-to-be-discovered attacks, and several attacks against Tor have been discovered (and fixed) over its history.
- shaddi 16y ago
  Right, but the idea behind direction finding is that you can triangulate the position of the transmitter. If you just have a bearing you have to search over a large area -- these links could be many kilometers long. Not saying it's impossible, but using highly directional antennas makes direction finding much more difficult.
ehsanul 16y ago
I'm no security expert, but I don't think you even need an out-of-band key exchange mechanism. Just use public key cryptography [1], as used in SSH/TLS/PGP/GPG. [1] http://en.wikipedia.org/wiki/Public-key_cryptography http://en.wikipedia.org/wiki/Public-key_cryptography
- deleted 16y ago
  [deleted]
- DougBTX 16y ago
  I was about to write this response, but I see that it is more clearly written in the wikipedia article already: Another potential security vulnerability in using asymmetric keys is the possibility of a man-in-the-middle attack, in which communication of public keys is intercepted by a third party and modified to provide different public keys instead. Encrypted messages and responses must also be intercepted, decrypted and re-encrypted by the attacker using the correct public keys for different communication segments in all instances to avoid suspicion. This attack may seem to be difficult to implement in practice, but it's not impossible when using insecure media (e.g. public networks such as the Internet or wireless communications). A malicious staff member at Alice or Bob's ISP might find it quite easy to carry out. In the earlier postal analogy, Alice would have to have a way to make sure that the lock on the returned packet really belongs to Bob before she removes her lock and sends the packet back. Otherwise the lock could have been put on the packet by a corrupt postal worker pretending to be Bob to Alice. The workaround is to either exchange the public keys out of band, or distribute a certificate which can be used to verify public keys out of band.

sown 16y ago

So what about for hidden tor services?

wmf 16y ago
I think one of the points of the rant is that you have no way to know whether Tor is safe or not; if Tor is compromised then you might as well assume that it's completely compromised, including hidden services.
x12x12x12 16y ago
Assuming you trust that hidden service? I imagine if all the nodes between you and that service had gone rogue, it would be possible to positively identify that you (or the Tor client IP at the entry point) communicated with that service, at what time, and generally how much was sent back and forth.

x12x12x12 16y ago

Security can succeed by making an attack economically or logistically impractical. You have to consider when using any such system: 1. What would it cost the adversary to pull off a successful attack to reveal your identity? Would it be worth it to the attacker to do so? 2. Are there easier, more obvious targets? I would say it's a possible useful tool of increasing that cost for a potential adversary above their threshold of resources and motivation. If I'm wrong, tell me where I posted this from, and I'll go hide in the woods.

corin_ 16y ago
Naturally depends on who you're trying to hide from. This article seems to have been written from the point of view of "the CIA are watching me", not "I don't want someone to hack my facebook profile". And based on that logic, you have to assume that the CIA (or whatever agency) won't chose who to spy on based on who will cost them the least money.
- pyre 16y ago
  The CIA won't choose to spend $1billion+ to spy on a single person unless they are really important.
  - wladimir 16y ago
    Most of the things he mentions are very cheap to pull off, though. Proxy honeypots, sniffing ISP internet connections, querying IPs, email surveillance -- the infrastructure is already in place they just have to type some commands. Cost: $0. On the other hand, actions that require actually sending men in suits and vans filled surveillance equipment can be costly. If they're doing that, you know you're in big trouble.
    - mootothemax 16y ago
      Most of the things he mentions are very cheap to pull off, though. Proxy honeypots, sniffing ISP internet connections, querying IPs, email surveillance -- the infrastructure is already in place they just have to type some commands. Cost: $0. I'm sorry but I have to jump in here - you're writing off an awful lost of resources under the banner of "they just have to type some commands."

jwhitlark 16y ago

When four people sit down to talk conspiracy, three are government agents, and the fourth is a fool.

ZoFreX 16y ago

Between the terrible grammar, grade school sentence structure, needless paranoia, senseless rambling and overall [citation needed]-ness of the article, I'm afraid I didn't really get the point. I thought it was going to explain why Tor is unsafe, yet it just made some broad speculative points and finished with a final jab in Tor's direction with no strength or conviction behind it.

iuguy 16y ago

I'll try to be careful with my words here (to avoid ambiguity more than anything else), but there are different programmes in different countries that provide different degrees of interception. In the UK we have the Regulation of Investigatory Powers Act 2000, which amongst other things forces service providers to keep logs of Internet activity for the police. These logs are typically of the order of IP address and connection type, not the actual data itself. This applies to pretty much all Internet access coming out of the UK somewhere along the line. Beyond the police there are means of intercepting specific Internet traffic. It's easier for me to talk about US interception capabilities at that level though (as it's more publicised). The FBI, NSA, CIA and (if IIRC but they might be colluding with another agency) the DHS all have their own independent capabilities for broad sweeps and targeted surveillance. These capabilities are exercised according to remit. The agencies have information sharing agreements with each other, and the relevant agencies have international sharing agreements with their counterparts e.g. UKUSA intelligence sharing agreements etc. If you want anonymity, you have to understand what you're trying to protect yourself from and (if possible) your adversary's capabilities. Having worked in countries with significant local interception capabilities that I do want to protect against, usually a properly configured VPN or SSH tunnel to a safe country is about as good as you're going to get without getting into government crypto (and if you're using government crypto in a hostile environment like that you're probably breaching some rule somewhere anyway). As to the question of whether or not Tor is safe, I assumed it was public knowledge that various countries' intelligence services ran monitored exit nodes for quite a while. I've seen malicious Tor exit nodes in investigations and have known people who've set them up for the express purpose of monitoring them.

unicornporn 16y ago

Not that the post actually brought up the Tor concept, but... I hate it when people diss the Tor concept by making the assumption that all uses of Tor requires an exit point. It doesn't. See torchat as an example. https://code.google.com/p/torchat/ https://code.google.com/p/torchat/