Lightweight Authentication for Email (and Web?) Ben Adida - PowerPoint PPT Presentation

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

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

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

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

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

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]

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

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.

Repudiability Alice Bob Eve Repudiability is about Privacy

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

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]

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

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

Questions?