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Edits to edits. Revert change to central gutter width; cut back down to under 15 pages.

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Nick Mathewson 2003-11-05 01:58:07 +00:00
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doc/latex8.sty
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@ -59,8 +59,8 @@
% set dimensions of columns, gap between columns, and paragraph indent % set dimensions of columns, gap between columns, and paragraph indent
\setlength{\textheight}{8.875in} \setlength{\textheight}{8.875in}
\setlength{\textwidth}{6.875in} \setlength{\textwidth}{6.875in}
%\setlength{\columnsep}{0.3125in} \setlength{\columnsep}{0.3125in}
\setlength{\columnsep}{0.26in} %\setlength{\columnsep}{0.26in}
\setlength{\topmargin}{0in} \setlength{\topmargin}{0in}
\setlength{\headheight}{0in} \setlength{\headheight}{0in}
\setlength{\headsep}{.5in} \setlength{\headsep}{.5in}

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doc/tor-design.tex
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@ -124,7 +124,7 @@ assumed padding between ORs, and in
later designs added padding between onion proxies (users) and ORs later designs added padding between onion proxies (users) and ORs
\cite{or-ih96,or-jsac98}. Tradeoffs between padding protection \cite{or-ih96,or-jsac98}. Tradeoffs between padding protection
and cost were discussed, and \emph{traffic shaping} algorithms were and cost were discussed, and \emph{traffic shaping} algorithms were
theorized \cite{or-pet00} that provide good security without expensive theorized \cite{or-pet00} to provide good security without expensive
padding, but no concrete padding scheme was suggested. padding, but no concrete padding scheme was suggested.
Recent research \cite{econymics} Recent research \cite{econymics}
and deployment experience \cite{freedom21-security} suggest that this and deployment experience \cite{freedom21-security} suggest that this
@ -1242,8 +1242,7 @@ points, informs him of her rendezvous point, and then waits for him
to connect to the rendezvous point. This extra level of indirection to connect to the rendezvous point. This extra level of indirection
helps Bob's introduction points avoid problems associated with serving helps Bob's introduction points avoid problems associated with serving
unpopular files directly (for example, if Bob serves unpopular files directly (for example, if Bob serves
material that the introduction point's neighbors find objectionable, material that the introduction point's community finds objectionable,
%XXX neighbors is a technical term
or if Bob's service tends to get attacked by network vandals). or if Bob's service tends to get attacked by network vandals).
The extra level of indirection also allows Bob to respond to some requests The extra level of indirection also allows Bob to respond to some requests
and ignore others. and ignore others.
@ -1256,9 +1255,7 @@ application integration is described more fully below.
\item Bob chooses some introduction points, and advertises them on \item Bob chooses some introduction points, and advertises them on
the DHT. He can add more later. the DHT. He can add more later.
\item Bob builds a circuit to each of his introduction points, \item Bob builds a circuit to each of his introduction points,
and waits. No data is yet transmitted. and waits. No more data is transmitted before the first request.
% XXX what do we mean No data? Bob obviously tells the IP about
% his hash-of-public key, auth scheme, etc
\item Alice learns about Bob's service out of band (perhaps Bob told her, \item Alice learns about Bob's service out of band (perhaps Bob told her,
or she found it on a website). She retrieves the details of Bob's or she found it on a website). She retrieves the details of Bob's
service from the DHT. service from the DHT.
@ -1272,7 +1269,7 @@ application integration is described more fully below.
first half of a DH first half of a DH
handshake. The introduction point sends the message to Bob. handshake. The introduction point sends the message to Bob.
\item If Bob wants to talk to Alice, he builds a circuit to Alice's \item If Bob wants to talk to Alice, he builds a circuit to Alice's
RP and provides the rendezvous cookie, the second half of the DH RP and sends the rendezvous cookie, the second half of the DH
handshake, and a hash of the session handshake, and a hash of the session
key they now share. By the same argument as in key they now share. By the same argument as in
Section~\ref{subsubsec:constructing-a-circuit}, Alice knows she Section~\ref{subsubsec:constructing-a-circuit}, Alice knows she
@ -1342,13 +1339,13 @@ those users can switch to accessing Bob's service via
the Tor rendezvous system. the Tor rendezvous system.
Since Bob's introduction points might themselves be subject to DoS he Since Bob's introduction points might themselves be subject to DoS he
could be faced with a choice between keeping many could have to choose between keeping many
introduction connections open or risking such an attack. In this case, introduction connections open or risking such an attack. In this case,
similar to the authentication tokens, he can provide selected users he can provide selected users
with a current list and/or future schedule of introduction points that with a current list and/or future schedule of introduction points that
are not advertised in the DHT\@. This is most likely to be practical are not advertised in the DHT\@. This is most likely to be practical
if there is a relatively stable and large group of introduction points if there is a relatively stable and large group of introduction points
generally available. Alternatively, Bob could give secret public keys available. Alternatively, Bob could give secret public keys
to selected users for consulting the DHT\@. All of these approaches to selected users for consulting the DHT\@. All of these approaches
have the advantage of limiting exposure even when have the advantage of limiting exposure even when
some of the selected high-priority users collude in the DoS\@. some of the selected high-priority users collude in the DoS\@.
@ -1460,11 +1457,11 @@ been shown to be effective against SafeWeb \cite{hintz-pet02}.
%possibility that multiple streams are exiting the circuit at %possibility that multiple streams are exiting the circuit at
%different places concurrently. %different places concurrently.
% XXX How does that help? Roger and I don't know. -NM % XXX How does that help? Roger and I don't know. -NM
It may slightly less effective against Tor, since It may be less effective against Tor, since
fingerprinting will be limited to fingerprinting will be limited to
the granularity of cells, currently 256 bytes. Further potential the granularity of cells, currently 256 bytes. Further potential
defenses include defenses include
larger cell sizes and/or minimal padding schemes to group websites larger cell sizes and/or padding schemes to group websites
into large sets. But this remains an open problem. Link into large sets. But this remains an open problem. Link
padding or long-range dummies may also make fingerprints harder to padding or long-range dummies may also make fingerprints harder to
detect.\footnote{Note that detect.\footnote{Note that
@ -1681,10 +1678,10 @@ blocking of valid requests, however, he should periodically test the
introduction point by sending it introduction requests, and making introduction point by sending it introduction requests, and making
sure he receives them. sure he receives them.
\emph{Compromise a rendezvous point.} Controlling a rendezvous \emph{Compromise a rendezvous point.} A rendezvous
point gains an attacker no more than controlling any other OR along point is no more sensitive than any other OR on
a circuit, since all data passing through the rendezvous is protected a circuit, since all data passing through the rendezvous is encrypted
by the session key shared by the client and server. with a session key shared by Alice and Bob.
\Section{Open Questions in Low-latency Anonymity} \Section{Open Questions in Low-latency Anonymity}
\label{sec:maintaining-anonymity} \label{sec:maintaining-anonymity}
@ -1747,8 +1744,8 @@ by batching and re-ordering packets, but it is unclear whether this could
improve anonymity without introducing so much latency as to render the improve anonymity without introducing so much latency as to render the
network unusable. network unusable.
A cascade topology may better defend against traffic confirmation by a A cascade topology may better defend against traffic confirmation by
large adversary through aggregating users, and making padding and aggregating users, and making padding and
mixing more affordable. Does the hydra topology (many input nodes, mixing more affordable. Does the hydra topology (many input nodes,
few output nodes) work better against some adversaries? Are we going few output nodes) work better against some adversaries? Are we going
to get a hydra anyway because most nodes will be middleman nodes? to get a hydra anyway because most nodes will be middleman nodes?
@ -1819,11 +1816,11 @@ and possibly better anonymity \cite{econymics}. More nodes means increased
scalability, and more users can mean more anonymity. We need to continue scalability, and more users can mean more anonymity. We need to continue
examining the incentive structures for participating in Tor. examining the incentive structures for participating in Tor.
\emph{Cover traffic:} Currently Tor avoids cover traffic because its costs \emph{Cover traffic:} Currently Tor omits cover traffic because its costs
in performance and bandwidth are clear, whereas its security benefits are in performance and bandwidth are clear, whereas its security benefits are
not well understood. We must pursue more research on both link-level cover not well understood. We must pursue more research on link-level cover
traffic and long-range cover traffic to determine some simple padding traffic and long-range cover traffic to determine whether some simple padding
schemes that offer provable protection against our chosen adversary. method offers provable protection against our chosen adversary.
%%\emph{Offer two relay cell sizes:} Traffic on the Internet tends to be %%\emph{Offer two relay cell sizes:} Traffic on the Internet tends to be
%%large for bulk transfers and small for interactive traffic. One cell %%large for bulk transfers and small for interactive traffic. One cell
@ -1837,10 +1834,9 @@ On the other hand, forward security is weakened because caches
constitute a record of retrieved files. We must find the right constitute a record of retrieved files. We must find the right
balance between usability and security. balance between usability and security.
\emph{Better directory distribution:} %Directory retrieval presents \emph{Better directory distribution:}
%a scaling problem, since
Clients currently download a description of Clients currently download a description of
the entire network state every 15 minutes. As the state grows larger the entire network every 15 minutes. As the state grows larger
and clients more numerous, we may need a solution in which and clients more numerous, we may need a solution in which
clients receive incremental updates to directory state. clients receive incremental updates to directory state.
More generally, we must find more More generally, we must find more