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@@ -574,8 +574,9 @@ for all transactions (and how to know that the pages you get have not
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been modified by the local attacker) to how to learn about a working
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bridge relay.
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-There's another catch though. We need to make sure that simply connecting
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-to a bridge relay doesn't set off red flags.
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+There's another catch though. We need to make sure that the network
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+traffic we generate by simply connecting to a bridge relay doesn't stand
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+out too much.
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%The following section describes ways to bootstrap knowledge of your first
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%bridge relay, and ways to maintain connectivity once you know a few
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@@ -633,7 +634,7 @@ in the certificate headers, yet it remains secure. Should we replace
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it with blank entries for each field, or should we research the common
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values that Firefox and Internet Explorer use and try to imitate those?
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-Lastly, Tor's TLS handshake involves sending two certificates in each
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+Worse, Tor's TLS handshake involves sending two certificates in each
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direction: one certificate contains the self-signed identity key for
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the router, and the second contains the current link key, signed by the
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identity key. We use these to authenticate that we're talking to the right
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@@ -646,6 +647,20 @@ certificates we present for each side.
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% for really, and how much work would it be to start acting like a normal
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% browser? -RD
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+Lastly, what if the adversary starts observing the network traffic even
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+more closely? Even if our TLS handshake looks innocent, our traffic timing
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+and volume still look different than a user making a secure web connection
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+to his bank. The same techniques used in the growing trend to build tools
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+to recognize encrypted Bittorrent traffic~\cite{bt-traffic-shaping}
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+could be used to identify Tor communication and recognize bridge
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+relays. Rather than trying to look like encrypted web traffic, we may be
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+better off trying to blend with some other encrypted network protocol. The
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+first step is to compare typical network behavior for a Tor client to
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+typical network behavior for various other protocols. This statistical
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+cat-and-mouse game is made more complex by the fact that Tor transports a
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+variety of protocols, and we'll want to automatically handle web browsing
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+differently from, say, instant messaging.
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+
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\subsection{Identity keys as part of addressing information}
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We have described a way for the blocked user to bootstrap into the
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Roger Dingledine