tor-webwml.git

@@ -456,44 +456,66 @@ director for information on making grants or major donations.

 used for?</a></h3>

 <p>

-Every Tor relay has a public decryption key (rotated once a

-week). When the Tor clients establish circuits, at each step they <a

-href="<svnsandbox>doc/design-paper/tor-design.html#subsec:circuits">demand

-that the Tor relay prove knowledge of its private key</a>. That way

+Tor uses a variety of different keys, with three goals in mind: 1)

+encryption (inside the Tor network), 2) authentication so you know you're

+talking to the relays you meant to talk to, and 3) signatures to make

+sure all users know the same set of relays.

+</p>

+

+<p>

+<b>Encryption</b>: first, all connections in Tor use TLS link encryption,

+so observers can't look inside to see which circuit a given cell is

+intended for. Further, the Tor client establishes an ephemeral encryption

+key with each relay in the circuit, so only the exit relay can read

+the cells. Both sides discard the circuit key when the circuit ends,

+so logging traffic and then breaking into the relay to discover the key

+won't work.

+</p>

+

+<p>

+<b>Authentication</b>:

+Every Tor relay has a public decryption key called the "onion key".

+When the Tor client establishes circuits, at each step it <a

+href="<svnsandbox>doc/design-paper/tor-design.html#subsec:circuits">demands

+that the Tor relay prove knowledge of its onion key</a>. That way

 the first node in the path can't just spoof the rest of the path.

+Each relay rotates its onion key once a week.

 </p>

 <p>

+<b>Coordination</b>:

 How do clients know what the relays are, and how do they know that they

-have the right keys for them? The directory servers provide a signed list

-of all the approved relays, and in that list are a set of self-signed

-certificates from each relay, specifying their keys, locations, exit

-policies, and so on. So unless the adversary can control a directory

-server (and starting in Tor 0.1.1.x, a threshold of the directory

-servers), he can't trick the Tor client into using other Tor relays.

+have the right keys for them? Each relay has a long-term public signing

+key called the "identity key". Each directory authority additionally has a

+"directory signing key". The directory authorities provide a signed list

+of all the known relays, and in that list are a set of certificates from

+each relay (self-signed by their identity key) specifying their keys,

+locations, exit policies, and so on. So unless the adversary can control

+a threshold of the directory authorities, he can't trick the Tor client

+into using other Tor relays.

 </p>

 <p>

-How do clients know what the directory servers are? The list comes with

-the Tor distribution. It hard-codes their locations and their public

-keys. So the only way to trick the user into using a fake Tor network

+How do clients know what the directory authorities are? The Tor software

+comes with a built-in list of location and public key for each directory

+authority. So the only way to trick users into using a fake Tor network

 is to give them a specially modified version of the software.

 </p>

 <p>

 How do users know they've got the right software? When we distribute

 the source code or a package, we digitally sign it with <a

-href="http://www.gnupg.org/">GNU Privacy Guard</a>. Also see the <a

+href="http://www.gnupg.org/">GNU Privacy Guard</a>. See the <a

 href="https://wiki.torproject.org/noreply/TheOnionRouter/VerifyingSignatures">instructions

 on how to check Tor's signatures</a>.

 </p>

 <p>

-In order to be absolutely certain that it's signed by the developers,

-you need to have met them in person and gotten a copy of their key

-fingerprint, or you need to know somebody who has. If you're concerned

-about an attack on this level, we recommend you get involved with the

-security community and start meeting people.

+In order to be certain that it's really signed by us, you need to have

+met us in person and gotten a copy of our GPG key fingerprint, or you

+need to know somebody who has. If you're concerned about an attack on

+this level, we recommend you get involved with the security community

+and start meeting people.

 </p>

 <hr />