diff --git a/doc/tor-design.tex b/doc/tor-design.tex index 505117461e..72e3eeea48 100644 --- a/doc/tor-design.tex +++ b/doc/tor-design.tex @@ -268,9 +268,9 @@ open problems. Modern anonymity designs date to Chaum's Mix-Net\cite{chaum-mix} design of 1981. Chaum proposed hiding sender-recipient connections by wrapping messages in several layers of public key cryptography, and relaying them -through a path composed of Mix servers. Mix servers in turn decrypt, delay, -and re-order messages, before relay them along the path towards their -destinations. +through a path composed of ``Mixes.'' These mixes in turn decrypt, delay, +and re-order messages, before relaying them along the sender-selected +path towards their destinations. Subsequent relay-based anonymity designs have diverged in two principal directions. Some have attempted to maximize anonymity at @@ -643,33 +643,35 @@ the connection are unique enough. (This is not to say that Tor offers no resistance to traffic confirmation; it does. We defer discussion of this point and of particular attacks until Section~\ref{sec:attacks}, after we have described Tor in more detail.) +% XXX We need to say what traffic analysis is: How about... +On the other hand, we {\it do} try to prevent an attacker from +performing traffic analysis: that is, attempting to learn the communication +partners of an arbitrary user. +% XXX If that's not right, what is? It would be silly to have a +% threat model section without saying what we want to prevent the +% attacker from doing. -NM +% XXX Also, do we want to mention linkability or building profiles? -NM -\SubSection{Known attacks against low-latency anonymity systems} -\label{subsec:known-attacks} -% Should be merged into ``Threat model'' and reiterated in Attacks. -NM +Our assumptions about our adversary's capabilities imply a number of +possible attacks against users' anonymity. Our adversary might try to +mount passive attacks by observing the edges of the network and +correlating traffic entering and leaving the network: either because +of relationships in packet timing; relationships in the volume of data +sent; [XXX simple observation??]; or relationships in any externally +visible user-selected options. The adversary can also mount active +attacks by trying to compromise all the servers' keys in a +path---either through illegitimate means or through legal coercion in +unfriendly jurisdiction; by selectively DoSing trustworthy servers; by +introducing patterns into entering traffic that can later be detected; +or by modifying data entering the network and hoping that trashed data +comes out the other end. The attacker can additionally try to +decrease the network's reliability by performing antisocial activities +from reliable servers and trying to get them taken down. +% XXX Should there be more or less? Should we turn this into a +% bulleted list? Should we cut it entirely? -We discuss each of these attacks in more detail below, along with the -aspects of the Tor design that provide defense. We provide a summary -of the attacks and our defenses against them in Section~\ref{sec:attacks}. - -Passive attacks: -simple observation, -timing correlation, -size correlation, -option distinguishability, - -Active attacks: -key compromise, -iterated subpoena, -run recipient, -run a hostile node, -compromise entire path, -selectively DOS servers, -introduce timing into messages, -directory attacks, -tagging attacks, -smear attacks, -entrapment attacks +We list these attacks and more, and describe our defenses against them +in Section~\ref{sec:attacks}. %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%