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Publius A Robust, Tamper Evident, Censorship Resistant WWW Based Publishing System

Publius A Robust, Tamper Evident, Censorship Resistant WWW Based Publishing System. Lorrie Cranor AT&T Research. Aviel Rubin AT&T Research. Marc Waldman NYU – CS Dept. Publius. Pen name used by authors of Federalist Papers

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Publius A Robust, Tamper Evident, Censorship Resistant WWW Based Publishing System

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  1. PubliusA Robust, Tamper Evident, Censorship Resistant WWW Based Publishing System Lorrie Cranor AT&T Research Aviel Rubin AT&T Research Marc Waldman NYU – CS Dept.

  2. Publius • Pen name used by authors of Federalist Papers • Federalist Papers influential in convincing NY state voters to ratify US constitution.

  3. Why Publish Anonymously? • Political Dissent • “Whistleblowing” • Radical Ideas • Human Rights Reports

  4. Publius Design Goals • Censorship Resistant • Tamper Evident • Source Anonymous • Updateable • Host Content Deniability • Persistent • Extensible • Freely Available

  5. Related Work • Connection Based Anonymity Hide identity of requestor • Location or Author Based Anonymity Hide identity of author or WWW server

  6. Connection Based Anonymity • Anonymizer HTTP proxy URL rewrite • Proxymate Formerly LPWA HTTP Proxy Pseudonym generation www.anonymizer.com www.proxymate.com

  7. Connection Based Anonymity • Onion Router Mix Network HTTP Proxy Developed • Crowds HTTP request via Crowd Dynamic Path generation www.onion-router.net www.research.att.com/projects/crowds

  8. Onion Routing Onion 1 Onion 2 Onion 3 Onion 4 “Hello World”

  9. Connection Based Anonymity • Freedom Similar to Onion Routing Implemented at transport layer Nym creation – allows multiple pseudonyms Supports HTTP, NNTP, POP3, Telnet , etc. http://www.freedom.net

  10. Location Based Anonymity • Rewebber (aka Janus) www.rewebber.de Author & Connection Based Tool HTTP Proxy URL Rewrite using public key crypto U=http://www.cs.nyu.edu/~waldman/publius.html Ek (M)=Encrypt message M with public key k http://www.rewebber.com/surf-encrypted/Ek(U)

  11. Location Based Anonymity • Taz & Rewebber Computers with public/private key pair Each runs HTTP proxy server Encryption similar to onion-routing TAZ servers translate name.taz to address Down server = document irretrievable www.firstserver.com:100/STOPREADINGTHISANDPAYATTENTIONTOTHESPEAKER

  12. Eternity Service • Ross Anderson (Univ. of Cambridge) • Network of servers – resists DOS attacks • Fee based • Files cannot be removed or updated • Digital Libraries

  13. Eternity Systems • Usenet Eternity Scaled Down Eternity System Usenet is storage medium Formatting using PGP, SHA1 Send to alt.anonymous.messages Server caches and performs updates Connect via WWW browser

  14. Eternity Inspired Systems • Freenet “Adaptive Network” Local caching Anonymous query, retrieval • Intermemory Self-replicating persistant RAM Donate hard disk space

  15. File Sharing Systems • Napster Peer-to-peer file sharing Peers can capture IP address or peer • Gnutella Anonymous query Peer to peer file transfer, IP capture

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

  17. Publius Servers Publius Server Table www.redcross.org whitehouse.gov whitehouse.gov www.redcross.org library.fr library.fr www.nyu.edu www.nyu.edu publius.uk publius.uk

  18. Publish Operation D = Document To Publish K=Key Shamir Secret Sharing K Share1 Share2 Share3 Share4 MD5 ( D . Sharei ) / Mod 5 = Index Into Server Table Index 0 = www.redcross.org Index 3 = www.nyu.edu Store D encrypted under K, and one Share on Server

  19. Publish Overview • Servers available to store content • Encrypt document with secret key K • Secret split key K into (m,k) shares (Shamir) • Store encrypted document and share on m servers • Form URL cryptographically tied to document • Distribute URL – Publius URL http://!publius!/1e6adsg673h0=hgj7889340=yareyoureadingthis=12asbnm8945

  20. Retrieve Overview • Break apart URL to discover document locations • Retrieve encrypted document and share from k locations • Reassemble Key K from shares • Decrypt retrieved document • Check for tampering • View in WWW browser

  21. http://!publius!/MD5(D.Share1 )MD5 (D.Share2)… http://!publius!/unReaDableUrL Index = MD5(D.Share1) Mod Table_Size From www.redcross.org Get Encrypted File, Share Key = combine Shares D = Decrypt File with Key Tamper Check = MD5(D.Share1) = value in URL Retrieve Operation

  22. Tradeoffs • N = # servers with Content & Share • K = # Shares needed to reconstruct the Key • Higher N Greater availability Harder to censor • Higher K Decreased performance Greater tamper protection Possibly Easier To Censor

  23. Update and Delete Operations • Update – “update” file, MD5(password.IP) • Delete – MD5(password .IP) • Threats – Place update file on server Brute force to delete files • URL contains update bit - Don’t accept updates • Publish Option – No Delete or Update

  24. Mutually Hyperlinked Content A B Publish B, Modify A, Publish A A B Publish B First – Invalid A Link Publish A First – Invalid B Link Problem: Content cryptographically tied to URL

  25. Hyperlinked Content Solution Hyperlink A AU Publish A, B Modify A, B Update Hyperlink Hyperlink Republish A,B B BU Update A,B Update

  26. User Interface Browser Based GUI Publius Proxy Internet http://!publius!/URL http://!publius!/PUBLISH http://!publius!/UPDATE http://!publius!/DELETE Store MIME type in first three bytes of file Send correct Content-Type to browser

  27. Threats & Limitations • Share Deletion or Corruption • Update File Deletion or Corruption • Denial of Service Attacks • Threats to Publisher Anonymity • “Rubber-Hose Cryptanalysis”

  28. 3 Week Server Recruitment Period • 100 Volunteers, Test Script distributed • 53 successfully installed test script • 44 successfully installed. • Proxy - server version of client, 9 volunteers • Must trust proxy – see file, password for Publish • Sees URL for retrieve • Over 550 client requests Live Trial (8/7/2000)

  29. Contributions & Availability • Automatic Tamper Checking Mechanism • Update / Delete Method • Publishing Mutually Hyperlinked Content • 1500 Lines of Perl • Uses Crypto++ 3.2 – Crypto Library (C++)

  30. Future Work • Remove dependence on server list - URL encodes locations, tamper check • Split content - Krawczyk – Information Dispersal • CPU payment scheme (Dwork, Naor) • Automatic replication across servers - Intermemory model

  31. Publius WWW Site Source Code & Technical Paper http://cs.nyu.edu/waldman/publius

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