Tor: a quick overview Roger Dingledine The Tor Project https://torproject.org/ 1 What is Tor? ● Online anonymity software and network ● Open source, freely available ● Community of researchers, developers, users, and relay operators 2 The Tor Project, Inc. ● 501(c)(3) non-profit organization dedicated to the research and development of tools for online anonymity and privacy 3 Estimated 300,000 daily Tor users 4 Threat model: what can the attacker do? Alice Anonymity network Bob watch Alice! watch (or be!) Bob! Control part of the network! 5 Anonymity isn©t cryptography: Cryptography just protects contents. “Hi, Bob!” “Hi, Bob!” Alice <gibberish> attacker Bob 6 Anonymity isn©t just wishful thinking... “You can't prove it was me!” “Promise you won't look!” “Promise you won't remember!” “Promise you won't tell!” “I didn't write my name on it!” “Isn't the Internet already anonymous?” 7 Anonymity serves different interests for different user groups. Anonymity “It's privacy!” Private citizens 8 Anonymity serves different interests for different user groups. Anonymity Businesses “It's network security!” “It's privacy!” Private citizens 9 Anonymity serves different interests for different user groups. “It's traffic-analysis resistance!” Governments Anonymity Businesses “It's network security!” “It's privacy!” Private citizens 10 Anonymity serves different interests for different user groups. Human rights “It's reachability!” “It's traffic-analysis activists resistance!” Governments Anonymity Businesses “It's network security!” “It's privacy!” Private citizens 11 Regular citizens don't want to be watched and tracked. Blogger Hostile Bob “I sell the logs.” Alice 8-year-old Incompetent Bob “Oops, I lost the logs.” Alice The AOL fiasco Sick Indifferent Bob “Hey, they aren't Alice my secrets.” Name, address, Consumer age, friends, (the network can track too) Alice interests (medical, financial, etc), Union unpopular opinions, member illegal opinions.... 12 Law enforcement needs anonymity to get the job done. Investigated “Why is alice.localpolice.gov reading suspect my website?” Officer Sting “Why no, alice.localpolice.gov! Alice target I would never sell counterfeits on ebay!” Organized “Is my family safe if I Crime go after these guys?” Witness/informer Anonymous “Are they really going to ensure Alice tips my anonymity?” 13 Businesses need to protect trade secrets ... and their customers “Oh, your employees are reading Competitor our patents/jobs page/product sheets?” “Hey, it's Alice! Give her the 'Alice' version!” Competitor AliceCorp “Wanna buy a list of Alice's suppliers? Compromised What about her customers? network What about her engineering department's favorite search terms?” 14 Governments need anonymity for their security “What will you bid for a list of Baghdad Untrusted IP addresses that get email from .gov?” Agent ISP Alice “Somebody in that hotel room just checked his Navy.mil mail!” Compromised “What does FBI Google for?” service “Do I really want to reveal my internal network topology?” Coalition Shared “Do I want all my partners to know member network extent/pattern of my comms with other Alice Defense in partners? Depth “What about insiders?” 15 Governments need anonymity for their security “How can I securely and quickly Homeland exchange vital info with every security sheriff's dept and Hazmat transporter network Govt. without bringing them into my secure web server network? Bob “Do I want every SIPRNET node to Defense in know where all the traffic on it is headed?” Depth “Can I hide where my MLS chat Hidden server/my automated regrader is?” Services Can my servers resist DDoS and physical attack even by authorized users?” 16 Journalists and activists need Tor for their personal safety Monitoring “Did you just post to that website?” ISP Activist/ Whistleblower Alice “Where are the bloggers connecting from?” Monitored “I run livejournal and track my users” website “Of course I tell China about my users” “What does the Global Voices website Filtered say today?” Blocked website “I want to tell people what's going on Alice in my country” Monitored “I think they're watching. I'm not even network going to try.” 17 18 You can't get anonymity on your own: private solutions are ineffective... Citizen Alice's small ... “One of the 25 users Alice anonymity net on AliceNet.” Officer Municipal Investigated Alice anonymity net suspect “Looks like a cop.” AliceCorp AliceCorp “It's somebody at anonymity net Competitor AliceCorp!” 19 ... so, anonymity loves company! Citizen ... “???” Alice Officer Investigated Alice Shared suspect “???” anonymity net AliceCorp Competitor “???” 20 Yes, bad people need anonymity too. But they are already doing well. Compromised botnet Stolen mobile phones Evil Criminal Alice Open wireless nets ..... 21 Current situation: Bad people on the Internet are doing fine Trojans Viruses Exploits Botnets Zombies Espionage DDoS Spam Phishing Extortion 22 The simplest designs use a single relay to hide connections. Bob1 Alice1 E(Bob3,“X”) “Y” Relay Alice2 E(Bob1, “Y”) “Z” Bob2 “X” Alice3 E(Bob2, “Z”) Bob3 (example: some commercial proxy providers) 23 One relay is a single point of failure. Bob1 Alice1 E(Bob3,“X”) “Y” Evil Alice2 E(Bob1, “Y”) Relay “Z” Bob2 “X” Alice3 E(Bob2, “Z”) Bob3 24 ... or a single point of bypass. Bob1 Alice1 E(Bob3,“X”) “Y” Irrelevant Alice2 E(Bob1, “Y”) Relay “Z” Bob2 “X” Alice3 E(Bob2, “Z”) Bob3 Timing analysis bridges all connections through relay ⇒ An attractive fat target 25 So, add multiple relays so that no single one can betray Alice. Alice Bob R1 R3 R4 R5 R2 26 A corrupt first hop can tell that Alice is talking, but not to whom. Alice Bob R1 R3 R4 R5 R2 27 A corrupt final hop can tell that somebody is talking to Bob, but not who. Alice Bob R1 R3 R4 R5 R2 28 Alice makes a session key with R1 ...And then tunnels to R2...and to R3 Alice Bob R1 R3 Bob2 R4 R5 R2 29 Snooping on Exit Relays ● Lots of press in 2007 about people watching traffic coming out of Tor. ● If you want end-to-end encryption (like https), then you need to get it separately. ● Tor hides your location; it doesn't magically encrypt all traffic on the Internet. ● Though Tor does protect from your local network. 30 Javascript, cookies, history, etc ● Javascript refresh attack ● Cookies, History, browser window size, user-agent, language, http auth, ... ● Mike Perry's Torbutton extension for Firefox fixes many of these, but not all 31 Flash is dangerous too ● Some apps are bad at obeying their proxy settings. ● Adobe PDF plugin. Flash. Other plugins. Extensions. Especially Windows stuff: did you know that Microsoft Word is a network app? 32 Choose how to install it ● Tor Browser Bundle: standalone Windows exe with Tor, Vidalia, Firefox, Torbutton, Polipo, e.g. for USB stick ● Vidalia bundle: Windows/OSX installer ● Tor VM: Transparent proxy for Windows ● “Net installer” via our secure updater ● Incognito Linux LiveCD 33 Usability for relay operators is key. ● Rate limiting: shouldn't eat too much bandwidth ● Exit policies: not everyone is willing to emit arbitrary traffic. allow 18.0.0.0/8:* allow *:22 allow *:80 reject *:* 34 35 36 The basic Tor design uses a simple centralized directory protocol. cache S1 Trusted directory Alice S2 Alice downloads Trusted directory consensus and cache descriptors from anywhere Authorities S3 Servers publish publish a consensus self-signed list of all descriptors descriptors. 37 Governments and other firewalls can just block the whole Tor network. S Alice S X S Alice X S 38 Alice Alice Alice Blocked Alice User Alice R3 Blocked Alice R4 User Bob Alice Blocked R2 User Alice R1 Blocked Alice User Alice Alice Blocked Alice User Alice Alice 39 40 Problem: Abusive users get the whole network blocked. Nice /. Alice X Tor network Jerk X Alice wikipedia X Some IRC networks Minimize scope of blocking? 41 Some abuses we©ve seen ● Ransom note via Hotmail ● Spam via Google Groups ● IRC jerks → DDoS on Tor relay ● Somebody downloads a Vin Diesel movie ● Wikipedia, Slashdot block posts 42 Tor is only a piece of the puzzle ● Assume the users aren't attacked by their hardware and software – No spyware installed, no cameras watching their screens, etc ● Assume the users can fetch a genuine copy of Tor: from a friend, via PGP signatures, etc. 43 Community ● Many tools make a big splash in the press – Censors need to feel in control; publicity removes the appearance of control ● Increase community diversity – Strong social network ● Funding – Donations, grants, contracts 44 3-Year Development Roadmap ● Improve Performance ● Client Safety ● Ease of Use and Understanding ● Core Research & Development https://torproject.org/press/ for details 45 Lessons? ● 1) Bad people don't need Tor. They're doing fine. ● 2) Honest people need more security/privacy/anonymity. ● 3) Law enforcement can benefit from it too. ● 4) Tor is not unbreakable. 46 Suggestions: Run a Tor node ● General Caveat: All advice is that of a theory guy with a PhD in Philosophical Logic That said... ● Run a Tor node (preferably on a firewall) – enclave communications to/from Tor protected – CAVEAT: An adversary that watches everything on your internet connection and the other end will see who communicates with that Tor node 47 Suggestion: Know your network ● Most exit nodes run by people who want to defend: democracy, privacy, consumers, crime victims, dissidents, bloggers, etc. – most do this on principle: at varying risk to themselves and their property – please be aware of impact on volunteer operators of watching/interacting with bad guys over Tor network – please be aware of Tor (and open relays and botnets) if only identifier you have to investigate is a network address – Talk to me or Tor Project whenever you can 48 Suggestions: Know your adversary ● Destination adversary: lock down applications, etc.