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Anonymity and Privacy Enhancing Technologies

Anonymity and Privacy Enhancing Technologies. Week 10 - November 2, 4. Cartoon dogs are anonymous on the Internet. Real dogs are anonymous on the Internet too!. The Internet can’t be censored. “The Net treats censorship as damage and routes around it.” - John Gillmore.

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Anonymity and Privacy Enhancing Technologies

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  1. Anonymity and Privacy Enhancing Technologies Week 10 - November 2, 4

  2. Cartoon dogs are anonymous on the Internet

  3. Real dogs are anonymous on the Internet too!

  4. The Internet can’t be censored “The Net treats censorship as damage and routes around it.” - John Gillmore

  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. 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. Request Request Reply Reply 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 Client Server

  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. 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. msg dest,msg B, C kC kB kA kC dest,msg C kC kB dest,msg kX = encrypted with public key of Mix X Mixes [Chaum81] Sender Destination Mix C Mix A Mix B Sender routes message randomly through network of “Mixes”, using layered public-key encryption.

  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. Crowds Crowd members Web servers 3 1 6 5 5 1 2 6 3 2 4 4

  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. 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. Publius design goals • Censorship resistant • Tamper evident • Source anonymous • Updateable • Deniable • Fault tolerant • Persistent • Extensible • Freely Available

  16. Publius Overview Publishers Servers Retrievers • Publius Content – Static content (HTML, images, PDF, etc) • Publishers – Post Publius content • Servers – Host Publius content • Retrievers – Browse Publius content

  17. Publishing a Publius document Publishers Servers • 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

  18. Retrieving a Publius document Publishers Servers Retrievers • 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

  19. Publius proxies Publishers Servers Retrievers PROXY PROXY • 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

  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. 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. 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. 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. Anonymizing agent Regulatoryandself-regulatoryframework Cookie cutter Secure channel Regulatoryandself-regulatoryframework P3P user agent Privacy tools The Internet User Service

  25. Anonymity tool applications • Communication • Publishing • Payments • Voting • Surveys • Credentials

  26. Homework 10 discussion • http://lorrie.cranor.org/courses/fa04/hw10.html

  27. Homework 11 • http://lorrie.cranor.org/courses/fa04/hw11.html

  28. Guest speaker • Ann Cavoukian

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