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Anonymous Communications and Tor: History and Future Challenges
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Number of users ≈ 0
Anonymous Communications and Tor:
History and Future Challenges
Remailers
Type-1 (Cypherpunk)
Sustainability
- Mix decrypts messages
- Uses PGP
Mixmaster (1998–)
- Layered encryption
- Batching and re-ordering
- Based on Chaum Mix (1981)
Who needs anonymity?
- Military personnel
- Law enforcement
- Bloggers
- Activists and whistle-blowers
- Ordinary people
Encryption doesn't work
TLS, PGP, S/MIME only hide what is being said
- Alice uploaded a gigabyte to CNN 6 hours before footage of human rights abuses were aired
- Bob, who just joined our criminal organization sent an encrypted email to the FBI a week before our boss got arrested
- Charlie keeps browsing our website of illegal material, maybe we should give him fake data?
Abuse
The Web
Equivalent systems
Nymble
Open proxies ≈ penet.fi
VPN ≈ Type-0
MixMinion ≈ Tor
Censorship resistance
Open problems
- Protocol obfuscation
- Scanning resistance
- Distribution mechanisms
Steven J. Murdoch
University of Cambridge Computer Laboratory
penet.fi (1993–1996)
- Simply stripped headers off emails sent via remailer
- Allowed replies to be sent
- Easy to use, but single point of compromise
- Shut down following compromise by CoS
Incentives
- Many users are unable to pay (tragedy of the commons)
- Giving better performance to users who contribute could reduce anonymity
- If money is changing hands, volunteers may give up
Mixminion (2002–)
- Fixed many problems
- Introduced replies
Web browsing is hard to secure
- Requires low latency
- High variability
- Low tolerance to padding
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