Sunday, August 3, 2014

On Nation States and the Limits of Anonymity - Tor

As a general rule, society has a preference for accountability.  For this reason, governments discourage anonymity.  Among the exceptions to this rule is citizen communications in resistance to government.  In this context, governments in general, and police states in particular, abhor anonymity.

Tor (formerly TOR ("The Onion Router")) is a tool for providing anonymity in the Internet.  It uses thousands of contributed routers, communicating using nested encryption, along a randomly selected path, such that when the communication finally appears in the clear, it cannot be traced back to its origin.  It raises the general problem of attribution in the Internet to a whole new level.  Its uses range from hiding browsing activity from routine state surveillance to hiding criminal or revolutionary communications.  

The following news item recently appeared:

 --Russian Government Seeking Technology to Break Tor Anonymity (July 25 & 28, 2014) 
The Russian government is offering a 3.9 million rubles (US $109,500) contract for a technology that can be used to identify Tor users. Tor was initially developed by the US Naval Research Laboratory and DARPA, but is now developed by The Tor Project, a non-profit organization. Tor is used by journalists and others who need to keep their identities hidden for their own safety; it is also used by criminals for the same purposes. The entrance fee for the competition is 195,000 rubles (US $5,500).

In my role as a member of the editorial board of SANS Newsbites, I made the observation that:

"In his most recent novel, Richard Clarke implied that NSA had targeted and broken TOR."

A reader responded in part:

"...more out of curiosity, didn’t the NSA have trouble cracking TOR, and at best, could only identify ingress and egress points?  As told by Team, anyway."

Now you have a context for this post.  I responded to him as follows:

Thanks for your note.  It allows me to know that the comment did what I had hoped it would do, i.e., raise questions.

I was deliberately vague and cited a questionable authority.

My working hypothesis, the advice I give my clients, is that nation states, at least wealthy ones, can read any message that they want to, rarely in near real time.  However, they cannot read every message that they want to.  Incidentally, that is why they store every cryptogram they see.  Decryption is expensive but storage is cheap.  The cost of decryption is falling but not nearly as fast as that of storage.  

When applied to Tor and anonymity, my assumption is similar.  I assume that nation states can identify the origin of any message that they want to, again, probably not in near real time.  However, they cannot identify the source of every message that they want to.   Again, that is why they require acres of storage.   Like breaking ciphers, breaking Tor is expensive.  However, given their resources and determination, it would be foolish to bet one’s life that they cannot do it.   They know the protocol better than anyone and they own some of the routers.

If you think about it, your question implies a point in time.  However, my guidance assumes that what they cannot do today, they will be able to do tomorrow.  Cheap storage buys them time.  It took them fifty years to crack Venona but they never gave up.

As with crypto, the resistance of Tor to nation states depends in part upon how much it is used.  The more they have to deal with, the less efficient they are.  Therefore, one wants to encourage its use while discouraging anyone from betting their life on it.

The net is that Tor is adequate to provide individual privacy.  It is probably adequate for most political discourse, at least in democratic states.  It becomes problematic when fomenting revolution or disclosing state secrets in authoritarian, or even wealthy but vindictive, countries.  

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