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Lightweight Authentication for Email (and Web?) Ben Adida ben@mit.edu PAW/DIG Meeting June 30th, 2005 (joint work with Susan Hohenberger and Ronald L. Rivest) Distributed Phishing Friends and Colleagues Jakobsson & Young 2005


  1. Lightweight Authentication for Email (and Web?) Ben Adida ben@mit.edu PAW/DIG Meeting June 30th, 2005 (joint work with Susan Hohenberger and Ronald L. Rivest)

  2. Distributed Phishing • Friends and Colleagues • Jakobsson & Young 2005

  3. Review SMTP Today DNS foo.com 2 MX MX Record mail.foo.com wonderland.com mail.foo.com outgoing incoming 3 mail server mail server 4 1 Alice Bob

  4. Review No Proof of Origin phish.com ? wonderland.com mail.foo.com outgoing incoming mail server mail server Alice Bob

  5. Review ID-Based Crypto "bob@foo.com" keyserver MPK MSK PK bob SK bob Alice Bob

  6. New ID-based Domains MPK foo.com MPK wonderland . com wonderland.com foo.com keyserver keyserver MSK wonderland . com MSK foo.com SK bob @ foo . com SK alice @ wonderland . com Alice Bob

  7. DNS to distribute New Master Public Keys DNS wonderland.com MPK wonderland . com Publish foo.com MPK foo . com wonderland.com key server MSK wonderland . com [DomainKeys]

  8. Email-Based New Authentication SK alice @ wonderland . com wonderland.com wonderland.com keyserver incoming MSK wonderland . com mail server [Gar2003] Alice

  9. Tweaks & Optimizations • Key Revocation - expiration date in the ID string: “ ben@mit.edu - 2005-04-26” • Domain Policies immediate deletion of spoofed emails. • Alternate Keyserver bootstrap individual users. Different Trust.

  10. Repudiability Alice Bob Eve Repudiability is about Privacy

  11. Ad-Hoc Group Sigs From: Alice To: Bob Subject: Account Your monthly balance is available at: http://wonderbank.com Signed: Alice or Bob

  12. Hijacking Keys for AHGS I signed this message, OR I have your secret key - Signature or Encryption key - Factoring-, DL-, BM-based algorithms - All known keypairs work! [AHR2005]

  13. Putting it All Together [AHR2005] DNS wonderbank.com MPK bank 1 1 PUBLISH PUBLISH foo.com MPK foo wonderbank.com foo.com key server key server MPK foo 3 6 MPK bank SK A 2 4 "bob@foo.com" PK B 9 From: Alice To: Bob Subject: Account 7 "alice@wonderbank.com" Your monthly balance is available at: http://wonderbank.com Alice Bob Signed: Alice or Bob PK A Wonderbank.com foo.com 5 8 Network Network

  14. Web Authentication? Request for Resource Web Server Request for Authentication PK Alice Signature on Nonce, Repudiable Against PK

  15. Questions?

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