1. Privacy Policy, Law and Technology Carnegie Mellon University Fall 2004 Lorrie Cranor http://lorrie.cranor.org/courses/fa04/ 1 Anonymity and Privacy Enhancing Technologies Week 10 - November 2, 4

2. Privacy Policy, Law and Technology Carnegie Mellon University Fall 2004 Lorrie Cranor http://lorrie.cranor.org/courses/fa04/ 2 Cartoon dogs are anonymous on the Internet

3. Privacy Policy, Law and Technology Carnegie Mellon University Fall 2004 Lorrie Cranor http://lorrie.cranor.org/courses/fa04/ 3 Real dogs are anonymous on the Internet too!

4. Privacy Policy, Law and Technology Carnegie Mellon University Fall 2004 Lorrie Cranor http://lorrie.cranor.org/courses/fa04/ 4 The Internet can’t be censored “The Net treats censorship as damage and routes around it.” - John Gillmore

5. Privacy Policy, Law and Technology Carnegie Mellon University Fall 2004 Lorrie Cranor http://lorrie.cranor.org/courses/fa04/ 5 Actually, none of this is true It is easy to adopt a pseudonym or a persona on the Internet, but it is difficult to be truly anonymous  Identities can usually be revealed with cooperation of ISP, local sys-admins, web logs, phone records, etc. The Internet can put up a good fight against censorship, but in the end there is still a lot of Internet censorship  Repressive governments and intellectual property lawyers have been pretty successful at getting Internet content removed

6. Privacy Policy, Law and Technology Carnegie Mellon University Fall 2004 Lorrie Cranor http://lorrie.cranor.org/courses/fa04/ 6 Degrees of anonymity Absolute privacy: adversary cannot observe communication Beyond suspicion: no user is more suspicious than any other Probable innocence: each user is more likely innocent than not Possible innocence: nontrivial probability that user is innocent Exposed (default on web): adversary learns responsible user Provably exposed: adversary can prove your actions to others More Less

7. Privacy Policy, Law and Technology Carnegie Mellon University Fall 2004 Lorrie Cranor http://lorrie.cranor.org/courses/fa04/ 7 The Anonymizer Acts as a proxy for users Hides information from end servers Sees all web traffic Adds ads to pages (free service; subscription service also available) http://www.anonymizer.com Anonymizer Request Reply ClientServer

8. Privacy Policy, Law and Technology Carnegie Mellon University Fall 2004 Lorrie Cranor http://lorrie.cranor.org/courses/fa04/ 8 Cryptography Basics Encryption algorithm  used to make content unreadable by all but the intended receivers E(plaintext,key) = ciphertext D(ciphertext,key) = plaintext Symmetric (shared) key cryptography  A single key is used is used for E and D D( E(p,k1), k1 ) = p Management of keys determines who has access to content  E.g., password encrypted email

9. Privacy Policy, Law and Technology Carnegie Mellon University Fall 2004 Lorrie Cranor http://lorrie.cranor.org/courses/fa04/ 9 Public Key Cryptography Public Key cryptography  Each key pair consists of a public and private component: k + (public key), k - (private key) D( E(p, k + ), k - ) = p D( E(p, k - ), k + ) = p Public keys are distributed (typically) through public key certificates  Anyone can communicate secretly with you if they have your certificate  E.g., SSL-base web commerce

10. Privacy Policy, Law and Technology Carnegie Mellon University Fall 2004 Lorrie Cranor http://lorrie.cranor.org/courses/fa04/ 10 B,kAkA CkBkB Mixes [Chaum81] Sender routes message randomly through network of “Mixes”, using layered public-key encryption. Mix A dest,msg kCkC CkBkB kCkC kCkC SenderDestination msg Mix C k X = encrypted with public key of Mix X Mix B

11. Privacy Policy, Law and Technology Carnegie Mellon University Fall 2004 Lorrie Cranor http://lorrie.cranor.org/courses/fa04/ 11 Crowds Users join a Crowd of other users Web requests from the crowd cannot be linked to any individual Protection from  end servers  other crowd members  system administrators  eavesdroppers First system to hide data shadow on the web without trusting a central authority http://avirubin.com/cacm.pdf

12. Privacy Policy, Law and Technology Carnegie Mellon University Fall 2004 Lorrie Cranor http://lorrie.cranor.org/courses/fa04/ 12 Crowds 1 2 6 3 5 4 3 5 1 6 2 4 Crowd membersWeb servers

13. Privacy Policy, Law and Technology Carnegie Mellon University Fall 2004 Lorrie Cranor http://lorrie.cranor.org/courses/fa04/ 13 Anonymous censorship-resistant publishing The printing press and the WWW can be powerful revolutionary tools  Political dissent  Whistle blowing  Radical ideas but those who seek to suppress revolutions have powerful tools of their own  Stop publication  Destroy published materials  Prevent distribution  Intimidate or physically or financially harm author or publisher

14. Privacy Policy, Law and Technology Carnegie Mellon University Fall 2004 Lorrie Cranor http://lorrie.cranor.org/courses/fa04/ 14 Anonymity increases censorship-resistance Reduces ability to force “voluntary” self- censorship Allows some authors to have their work taken more seriously  Reduces bias due to gender, race, ethnic background, social position, etc. Many historical examples of important anonymous publications  In the Colonies during Revolutionary War when British law prohibited writings suggesting overthrow of the government  Federalist papers

15. Privacy Policy, Law and Technology Carnegie Mellon University Fall 2004 Lorrie Cranor http://lorrie.cranor.org/courses/fa04/ 15 Publius design goals Censorship resistant Tamper evident Source anonymous Updateable Deniable Fault tolerant Persistent Extensible Freely Available

16. Privacy Policy, Law and Technology Carnegie Mellon University Fall 2004 Lorrie Cranor http://lorrie.cranor.org/courses/fa04/ 16 Publius Overview Publius Content – Static content (HTML, images, PDF, etc) Publishers – Post Publius content Servers – Host Publius content Retrievers – Browse Publius content PublishersServersRetrievers

17. Privacy Policy, Law and Technology Carnegie Mellon University Fall 2004 Lorrie Cranor http://lorrie.cranor.org/courses/fa04/ 17 Publishing a Publius document Generate secret key and use it to encrypt document Use “secret splitting” to split key into n shares  This technique has special property that only k out of n shares are needed to put the key back together Publish encrypted document and 1 share on each of n servers Generate special Publius URL that encodes the location of each share and encrypted document – example: http://!publius!/1e6adsg673h0==hgj7889340==345lsafdfg PublishersServers

18. Privacy Policy, Law and Technology Carnegie Mellon University Fall 2004 Lorrie Cranor http://lorrie.cranor.org/courses/fa04/ 18 Retrieving a Publius document Break apart URL to discover document locations Retrieve encrypted document and share from k locations Reassemble key from shares Decrypt retrieved document Check for tampering View in web browser PublishersServersRetrievers

19. Privacy Policy, Law and Technology Carnegie Mellon University Fall 2004 Lorrie Cranor http://lorrie.cranor.org/courses/fa04/ 19 Publius proxies Publius proxies running on a user’s local machine or on the network handle all the publish and retrieve operations Proxies also allow publishers to delete and update content PublishersServersRetrievers PROXYPROXY PROXYPROXY

20. Privacy Policy, Law and Technology Carnegie Mellon University Fall 2004 Lorrie Cranor http://lorrie.cranor.org/courses/fa04/ 20 Threats and limitations Attacks on server resources  100K Content Limit (easy to subvert)  Server limits # of files it will store  Possibility: use a payment scheme Threats to publisher anonymity “Rubber-Hose Cryptanalysis”  Added “don’t update” and don’t delete bit Logging, network segment eavesdropping Collaboration of servers to censor content  A feature?

21. Privacy Policy, Law and Technology Carnegie Mellon University Fall 2004 Lorrie Cranor http://lorrie.cranor.org/courses/fa04/ 21 Discussion Technology that can protect “good” speech also protects “bad” speech What if your dog does publish your secrets to the Internet and you can't do anything about it? Is building a censorship-resistant publishing system irresponsible? If a tree falls in a forest and nobody hears it….

22. Privacy Policy, Law and Technology Carnegie Mellon University Fall 2004 Lorrie Cranor http://lorrie.cranor.org/courses/fa04/ 22 For further reading Publius web site http://cs.nyu.edu/waldman/publius.html Publius chapter in Peer-to-Peer: Harnessing the Power of Disruptive Technologies edited by Andy Oram The Architecture of Robust Publishing Systems. ACM Transactions on Internet Technology 1(2):199-230 http://doi.acm.org/10.1145/502152.502154

23. Privacy Policy, Law and Technology Carnegie Mellon University Fall 2004 Lorrie Cranor http://lorrie.cranor.org/courses/fa04/ 23 Anonymous email Anonymous remailers allow people to send email anonymously Similar to anonymous web proxies  Send mail to remailer, which strips out any identifying information (very controversial)  Johan (Julf) Helsingius ~ Penet Some can be chained and work like mixes http://anon.efga.org/Remailers

24. Privacy Policy, Law and Technology Carnegie Mellon University Fall 2004 Lorrie Cranor http://lorrie.cranor.org/courses/fa04/ 24 Regulatory and self-regulatory framework ServiceUser The Internet Secure channel P3P user agent Cookie cutter Anonymizing agent Privacy tools

25. Privacy Policy, Law and Technology Carnegie Mellon University Fall 2004 Lorrie Cranor http://lorrie.cranor.org/courses/fa04/ 25 Anonymity tool applications Communication Publishing Payments Voting Surveys Credentials

26. Privacy Policy, Law and Technology Carnegie Mellon University Fall 2004 Lorrie Cranor http://lorrie.cranor.org/courses/fa04/ 26 Homework 10 discussion http://lorrie.cranor.org/courses/fa04/hw 10.html http://lorrie.cranor.org/courses/fa04/hw 10.html

27. Privacy Policy, Law and Technology Carnegie Mellon University Fall 2004 Lorrie Cranor http://lorrie.cranor.org/courses/fa04/ 27 Homework 11 http://lorrie.cranor.org/courses/fa04/hw 11.html http://lorrie.cranor.org/courses/fa04/hw 11.html

28. Privacy Policy, Law and Technology Carnegie Mellon University Fall 2004 Lorrie Cranor http://lorrie.cranor.org/courses/fa04/ 28 Guest speaker Ann Cavoukian