1. Publius A Robust, Tamper Evident, Censorship Resistant WWW Based Publishing System
Lorrie Cranor
AT&T Labs
Avi Rubin
AT&T Labs
Marc Waldman
New York University

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

3. Why Publish Anonymously?
Political Dissent
“Whistleblowing”
Radical Ideas

4. Related Work Connection Based Anonymity
Hide identity of requestor
Anonymizing proxies (for example Anonymizer.com)
Freedom (Zero-Knowledge Systems)
Crowds (AT&T Labs-Research)
Location or Author Based Anonymity
Hide identity of author or WWW server
USENET Eternity System
Freenet
Intermemory
Rewebber

5. Publius Design Goals Censorship Resistant Tamper Evident
Source Anonymous
Updateable
Host Content Deniability
Fault tolerant
Persistent
Extensible
Freely Available

6. 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

7. 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:

8. 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

9. 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

10. Threats & Limitations Share deletion or corruption
Update file deletion or corruption
Denial of service attacks
Threats to publisher anonymity
“Rubber-hose cryptanalysis”

11. Publius trial Trial began August 7 and will last at least two months
Over 40 individuals and organizations in several countries volunteered to host Publius servers
Over a dozen public Publius proxies
Complete source code for servers and proxies has been released
Code has been configured to accept files no larger than 100K
Users have given us lots of good suggestions for improvements; so far no major problems
System designed for censorship resistance, but much current interest in intellectual property issues

12. For more information See the Publius web site
Download code and technical paper
Read about Publius in the news
Configure your browser to use a Publius proxy
View sample Publius content