Nathan Evans did the last talk on the first night of Defcon called De-TOR-iorate Anonymity. It had a lot of people sweating on the Tor mailing list and even generated a huge debate about whether Tor should even be attempted to be used on a multi-purpose system versus a dedicated machine or virtual machine like JanusVM or AnonymOS. The information was pretty thick to process at the time, but a few minutes later, it finally sunk in. Here's how it works.

Overview of Tor

A quick review of how Tor works. Tor is a anonymity tool that creates a circuit of proxy servers to relay connections through. For instance, in the figure below we see Alice trying to connect to Bob. Alice sends traffic to node 1, node 1 relays that traffic to node 5, node 5 relays that traffic to node 8 and node 8 finally sends the request to Bob. If Bob replies, the data travels back the direction that it came. Simple enough?

Overview of Attack

Nathan's attack would fall under the "partitioning" label as the goal of the attack is to partition the Tor network smaller and smaller until it can find the entry node the user is coming from. Because this attack assumes you have control of the exit node, obtaining the entry node confirms the second node used as a relay thus showing every node in a user's circuit. This makes Tor as anonymous as a single proxy.

Circular Circuits

Nathan found that an attacker can create looped circuits. That is Node 1 relays to Node 2 and then relays to Node 3 but at Node 3 an EXTEND command is issued so the circuit length is increased infinitely. This causes the queue of traffic waiting to be relayed to fill up and the latency to increase by a large amount.

Why it works

Doing a DoS attack and measuring the latency is not new. It was actually talked about at last year's Defcon. The difference with this attack is the attacker actually creates circular circuits so nodes are actually looping traffic back to the beginning instead of relaying properly.

This is why the attack worked:

• Tor is hard coded to only uses 3 nodes in a circuit(debatable whether or not to change)
• Tor does not provide padding to keep latency at the same rate (and never will)
• Tor allows for infinite circuit lengths (to be fixed in proposal 110)

The Attack

To attack the network, he used the following environment

1. a "Bad Exit Node" owned by the attacker
2. Tor client used to generate circular circuits (Defined as "DoS Client")
3. Web server to act as the destination and to keep track of latency (Defined as "DoS Server")
4. Normal user that is using the Bad Exit Node ("Alice")

The attack is done by a denial-of-service attack on many nodes using circular circuits discussed above. If the user's latency stays low during a circular circuit creation, then the attacker knows that the entry node is NOT one of the DoS'd relays and tries different nodes. In this case, latency is measured by injecting a javascript command to ping a web server collecting stats. The process of generating circular circuits and recording the results is repeated until the user's latency increases substantially at which time the attacker knows that the entry node is one of the three nodes used in the last DoS attack.

Example

In this figure, you can see that Alice is trying to connect to Bob via nodes 1, 5, and the Bad Exit Node that is owned by the attacker. During this time the attacker is creating circular circuits between 1, 2, and 3 which generate large amounts of traffic causing a slow down.

The Fix

Tor has been been updated at least 3 times since writing this blog. Among many other bug fixes and feature additions are the changes related to Proposal 110. This is the proposal to change Tor to handle circular circuits. The proposal splits up relay requests into "Relay" and "Relay_Early." Relay requests do not have the ability to issue the EXTEND command that is used to generate the circular circuits and Relay_Early can as these would be the beginning of the circuits.

The 0.2.0.30 version also makes an addition to block "risky" extend cells.

Relays now reject risky extend cells: if the extend cell includes a digest of all zeroes, or asks to extend back to the relay that sent the extend cell, tear down the circuit. Ideas suggested by rovv.

The fix is not complete. They are still implementing parts of proposal 110. They have to maintain backwards compatibility in case a version 1 circuit is created.

External Links

http://www.torproject.org - Tor Project Website
https://www.torproject.org/svn/trunk/doc/spec/proposals/110-avoid-infinite-circuits.txt - Details of the proposal for the fix
http://archives.seul.org/or/talk/Aug-2008/msg00148.html - just for accuracy's sake, Roger Dingledine's follow up to my explanation on the or-talk list
http://web.cs.du.edu/~natevans/ - Nathan Evan's website. Nothing there really
https://www.defcon.org/images/defcon-16/dc16-presentations/defcon-16-evans-grothoff.pdf - Original powerpoint presentation called De-Tor-iorate Anonymity
https://www.torproject.org/svn/trunk/ChangeLog - the always updating changelog of Tor

Last year was my first year at Defcon so I was sucking up as much information as possible but generally I just went to the talks and then back to the room to play with the things that I had learned.  I didn't get into the social scene very much.

This year I still attended a ton of the talks but instead of taking time to go back to the room and play, my friends and I made more of an effort to get into the Defcon social scene.

Overall Experience

Just like last year I had a blast but I think even more this year because of some of the people we met. I've seen some posts complaining about the situation at Defcon about how it was too crowded and they missed some talks because of this. It sounds to me like a lot of people have gone to things like Microsoft Events where you stand around some muffins and coffee and then sit through 2 hours of talks.Defcon hacks the conservative convention idea and takes into account the amount of hackers that have ADD.They offer 5 tracks of talks at the same time, lock picking training, wireless village, general hang outs, and more. Then when the talks are all done, there are parties all over the city. It's not cup of coffee, stand in line, polite conversation kind of gathering but rather a red bull and vodka, bum rush, punch in the face cluster of people from all over world meeting to show solidarity in the hacker community. At least that's the my ideal perspective of what Defcon should be, it may be growing in a different direction.

List of talks I attended:

• Welcome by DT & Making the DEFCON 16 Badge with Joe "Kingpin" Grand
• Clinton Wong - Web Privacy & Flash Local Shared Objects.
• Roger Dingledine -Security and anonymity vulnerabilities in Tor: past, present, and future
• Robert Ricks -New Tool for SQL Injection with DNS Exfiltration.
• Magnus Bråding -Generic, Decentralized, Unstoppable Anonymity: The Phantom Protocol.
• Eric Schmiedl -Advanced Physical Attacks: Going Beyond Social Engineering and Dumpster Diving Or, Techniques of Industrial Espionage
• Fyodor -NMAP-Scanning the Internet.
• Matt Yoder-Death Envelope: Medieval Solution to a 21st Century Problem.
• John Fitzpatrick -Virtually Hacking.
• Nathan Evans -De-TOR-iorate Anonymity
• Movie Night With DT: Premiere of "Hackers Are People Too
• Cameron Hotchkies-Under the iHood.
• Jay Beale-Owning the Users with Agent in the Middle.
• Luciano Bello & Maximiliano Bertacchini-Predictable RNG in the Vulnerable Debian OpenSSL Package, the What and the How.
• Panel: All your Sploits (and Servers) are belong to us.
• Mike Perry-365-Day:Active https cookie hijacking.
• Tony Howlett-The death of Cash: The Loss of anonymity & other danger of the cash free society.
• Ryan Trost-Evade IDS/IPS Systems using Geospatial Threat Detection.
• Rick Hill-War Ballooning-Kismet Wireless "Eye in the Sky"
• Jay Beale-They're Hacking Our Clients! Introducing Free Client-side Intrustion Prevention.
• DAVIX Visualization Workshop
• Stealing the Internet

Tor

I've been following Tor for a while now so it was interesting to go to the two Tor specific talks – both about vulnerabilities in Tor. Roger Dingledine presented a general overview of past, present, and future vulnerabilities in the Tor network and Nathan Evans went over a specific vulnerability which allowed an attacker to find out all nodes in a circuit. Both talks were interesting and I'm going to go into much more detail in future blog entries.

Sidejacking Redux

Last year, the concept of sidejacking was in its infancy. Sidejacking or session hijacking is when an attacker uses a man in the middle to steal the current session of something a user is accessing. For instance, with this attack, an attacker could steal the cookies used to authenticate a person's gmail account which would grant the attacker access to Gmail and all other Google services for the amount of time that session was valid. This year Jay Beale of the company Intel Guardians released a tool called “The Middler” which automates this process and Mike Perry of Riverbed and the Tor Project pointed out a flaw in the way that some companies have tried to protect users from this exploit.

Since last year, services like Gmail have offered SSL encryption to protect from this attack but they didn't force users to use SSL which lead to Mike Perry's talk. He pointed out an attack on a Gmail  where even though the user was using an SSL connection, the cookie could be transmitted in clear text allowing a session hijack. This was done by doing a MITM attack, using a tool to check which online service the user was using, inject a piece of html that pointed to the non-SSL encrypted version of that online service and then perform a session hijack after reading in the credentials. He even pointed out a simple fix that he has told Gmail and Yahoo about where you can set a bit in the cookie to only transmit in SSL.

War-Ballooning

One of the most fun talks that I attended was Rick Hill's War-Ballooning demonstration. They were planning on doing a live demo from the roof of the Riveria but at the last minute, some authorities decided to stop them. War-Ballooning was a development of last years idea of War-Rocketing which shot a rocket in the air and then searched for wireless signals while it parachuted to the ground. This year they took a professional balloon that was used by photographers for shooting aerial shots, attached a cooler filled with various wireless gear, and configured a orbital webcam that controlled which direction the yagi antenna was pointing. So they gave a video of the demonstration which was recorded the day before in a park five miles out of town. For added drama, they used Kismet's feature to read wireless networks out loud as it found them. They had the balloon up for ten minutes and found over 300 wireless signals as it broadcast a 7 mile radius. 30% of those were unsecured.

Hackers Are People Too - Ashley Schwartau

And how could I forget to add something about my acting debut in the documentary Hackers Are People Too which was premiered at Defcon XVI. Well ok, maybe I was on the screen for less than 2 seconds and I wasn't quoted as saying anything but hey, to be in a hacker documentary was really cool. Ashley even recognized me when I came up to her vendor booth. But enough of my vanity, the documentary was so cool and people really should pick it up to show to their friends and family and get the scarey idea of what hackers are out of their heads.

External Links

http://www.hackersarepeopletoo.com - link to the Hackers Are People Too official website (BUY BUY BUY!!!)
http://fscked.org/ - Mike Perry's website
http://www.defcon.org-Defcon
http://www.intelguardians.com/ - Intel Guardians will soon be releasing "The Middler"
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I arrived Thursday morning to Las Vegas in an attempt to do some of the pre-Defcon social events this year. We posted our room availability on the Defcon forums and picked up two roomates to help with the costs; Riot and Matt.

I reserved the "deluxe" room at the Riveria which although being nicer, doesn't have any more space than the non-deluxe. It does look much more romantic but filling it with 4 guys takes care of that feeling pretty quickly.

Badges this year include an IR port, an SD slot, and supposedly a way to shut off all TV's in a certain radius, and a transmit mode that may allow you to talk to other badges as you walk around the floor.

Ethical Hackers

Ethical Hackers was doing a get together at Hofbrauhaus, a German brew house at 8:00pm. Dan who runs the site was putting it all together and had a $500 tab for us to use. The whole event was a lot of fun and had a lot of interesting people. Timmy of Red Rock Security, Brian of Cisco, Ed of Intel Guardians, David an extreme baby sitter, Collin of Training Camp, Mike the Military Vet, Naps, and a bunch of others of whom I may have forgotten their names. Check out ChicagoCon for anyone that will be in the area. Sounds like a very worthwhile event. I think the whole get together was a success.

EFF Summit

We also grabbed a few of the guys to make it back to the EFF Summit at the top of the Monaco tower back at the Riveria. Donations were $40 to get in and included a one year membership. Once the sound system was working at around 10:30 or 11:00, some of the EFF guys went up to talk about some of the cases that were won and some of good things that the EFF does. I think it was kind of preaching to the choir but the event went pretty well.

External Links

http://www.ethicalhackers.net
Red Rock Security
ChicagoCon
Intel Guardians