5 October 2013
NSA Informed on Tor by Roger Dingledine
Talk by Roger Dingledine of Torproject.org at the NSA
By Washington Post Staff, Published: October 4
Below are the National Security Agencys notes from a talk given by
Roger Dingledine, director and one of the original developers of Torproject.org,
at the agency in November 2007.
[The original document was not provided by Washington Post.]
DYNAMIC PAGE HIGHEST POSSIBLE CLASSIFICATION
TOP SECRET // COMINT // REL TO USA, AUS, CAN, GBR, NZL
Roger Dingledine at NSA NOV 2007
* 1 (U) Talk by Roger Dingledine at NSA, 11/01/2007 at R&E (Sponsored
by NSA RT)
o 1.1 (U) Who are TOR Customers?
o 1.2 (U) Anonymity System Concepts
o 1.3 (U) TOR Issues
(U) Talk by Roger Dingledine at NSA, 11/01/2007 at R&E (Sponsored
by NSA RT)
(U) Roger Dingledine, now of Torproject.org, was one of the principle inventors
or TOR. Current usage statistics quoted are 200K users and 1K servers. When
asked about trends, he had no concrete data - Being a non-profit open-source
effort, the collector of statistics has not been active recently.
(U) The obligatory Anonymity is not equal to Cryptography and
Anonymity is not equal to Steganography admonishments were given
(U) Who are TOR Customers?
(U) Mr. Dingledine mentioned that the way TOR is spun is dependent on who
the spinee is. Using the typical (in the cryptography world),
Alice and Bob as communicants, he described several Alices:
(U) 1. Blogger Alice, who wants to be able to write to a blog in an anonymous
(U) 2. 8 yr. old Alice, who wants to be able to post to sites for children
in a way insuring her true name and location are not discovered.
(U) 3. Sick Alice, who want to research information on her illness on the
Internet while not enabling anyone to determine her true name and location.
(U) 4. Consumer Alice, who wants to research possible purchases without having
a database of her marketing habits being built without (or with her weak)
(U) 5. Oppressed Alice, who lives in a repressive country (no or limited
free speech) and wants to talk about things contrary to her governments
positions. The countries he used as examples were France, Germany (prohibitions
on fascist writings?) and the US (not sure what he meant here?).
(U) 6. Turning to Business Alice, we had examples of companies
not wanting to give up their business secrets to competitors via their Internet
usage patterns. An anecdote was given of some business getting a different
HTML page displayed when the same URL was accessed with and without TOR.
(U) 7. Law Enforcement Alice was concerned with the ability of
anonymous agents/informants to really main anonymous when contacting their
law enforcement ties.
(U) Anonymity System Concepts
(U) Running ones own anonymity service vs. Using a 3rd party service: If
one uses ones own service, its pretty obvious who the user is :-)
(U) Low Latency Anonymity Service vs. High Latency Anonymity Service: The
difference is in how paranoid someone really is. In a Low Latency Anonymity
Service (all common proxies, TOR, others), there is a rerouting through some
number of proxies, but there is no attempt to reorder packets or artificially
introduce latencies. The result is something which can be used for most web
and instant messaging / chat applications with only minimal notice of delays
by the user. In a high latency service, proxies attempt to randomly reorder
an delay packet so that it is harder to track traffic. Such systems are really
only useful for such protocols as email.
U) The most recent and advanced High Latency anonymity service was the
/*MixMinion*/ family of open source projects. Mr. Dingledine was one of the
key developers of these. His opinion is that the very limited utility of
such projects has caused them to wither on the vine. He does *not* see any
major development in such services for other than research in the forseeable
future. Another key point is that the degree of anonymity in any system is
proportional to the number of users. If noone is using any of the high latency
systems, why bother. This proportionality is one of the ideas Mr. Dingledine
refers to as a /tension/ in the world of anonymity systems.
(U) TOR Issues
(U) The short description of TOR for the reader is as follows: The user,
via his/her TOR client, queries one of 5 directory servers for the current
list of TOR nodes. Using metrics such as availability and bandwidth in
conjunction with random choice, a set of 3 proxies is chosen for a
circuit. It is this circuit which is used, with a unique layer
of encryption on each link, for anonymous Internet interactions.
(U) The lifetime of a circuit, a tuneable parameter, is another /tension/,
this one specific to TOR. The longer the circuit life, the more various traffic
that may transit it, forming a knowable relationship between the traffic
streams. Too short of a lifetime means too much time/CPU is spent building
circuits. The original default lifetime was 30 seconds but is now 10 minutes.
Everything is tweakable in TOR, so a user if free to choose his/her own circuit
lifetime. But this is dangerous, as a unique circuit lifetime could easily
become a user identification feature :-).
(U) Mr. Dingeldine was asked about the concrete choice of a 3-long circuit.
This is unlikely to change soon, as it appears to be a very suitable tradeoff.
(U) The mention of SOCKS proxies, such as /*Privoxy*/ as a bump in the chain
before TOR was mentioned. These proxies can intercept and cleanup things
such as cookies to further help anonymity.
(U) The current owner of TOR is torproject.org, a US registerd
501(C) non-profit organization, of which Mr. Dingledine is a principal. In
addition to specific technology issues such as scaling, other categories
of work are:
(U) 1. Usability (Targetting the ability of other than tech-savvy users to
embrace the technology)
2. Incentives (Trying to get more people to run TOR servers)
3. Design for Scalability/Decentralization
3a. Regarding scalability of the TOR network, Mr. Dingledine proffered the
guess that 2000-3000 is a rough upper limit on the number of nodes in the
pool before a new topology may be advised.
3b. Decentralization means less reliance on a very small set of trusted Directory
Servers (curently 5)
4. Continued research on attacks and the mitigation thereof.
5. Continued provision of documentation and user technical support.