1. Systematization of Knowledge
Secure Messaging
Systematization of Knowledge
Nik Unger, Sergej Dechand,
Joseph Bonneau, Sascha Fahl, Henning Perl, Ian Goldberg, Matthew Smith

2. Increasing demand for secure messaging1
Motivation
Increasing demand for secure messaging1
1Public Perceptions of S&P in the Post-Snowden Era (Pew Internet Research)

3. Which messenger should I use?

4. Messaging specific research challenges
Relevant for Academia?
Academia vs. practice
EFF Scorecard (>100 tools)
Individual threat models and features
Messaging specific research challenges
Academic work often ignored in practice
In-the-wild approaches unknown in academia
Sparsely covered in academia but various tools in the wild

5. Evaluation criteria (academic concepts)
Our Goal
Overview
Evaluation criteria (academic concepts)
Security
Usability
Adoption
Highlight research challenges & perspectives

6. Conversation Security Transport Privacy
Problem Areas
Trust Establishment
Long-term key verification
Conversation Security
Crypto stuff
Transport Privacy
Meta-data protection

7. Conversation Security Transport Privacy
Problem Areas
Trust Establishment
Long-term key verification
Conversation Security
Crypto stuff
Transport Privacy
Meta-data protection

9. State of the art in Practice
“Trusted” third parties
Key directories
Manual verification
Mostly optional

10. Manual Verification

11. Optional Verification

12. Transparency (Academic)
“Certificate Transparency for user keys”
Practical issues
(Inattentive) end users
Key changes
Multi-device management
Privacy preservation
Key change detected
The server has published an unexpected key for you. If you haven’t re-installed this app recently, this may mean somebody is trying to intercept your communications.
Check list of devices and keys

13. Alternative Solutions
Keybase
OneName
Namecoin …

14. Conversation Security Transport Privacy
Problem Areas
Trust Establishment
Long-term key verification
Conversation Security
Crypto stuff
Transport Privacy
Meta-data protection

15. Conversation Security
Security on message level
Confidentiality, Integrity, Authentication
Forward / Backward Secrecy …
Asynchronous
Users go offline
Unreliable connections
Without user interaction

16. Forward / Backward Secrecy
Easy in the web
Most tools in practice
Without PFS
Require synchronicity
Limited forward secrecy with key derivation
Axolotl allows asynchronous PFS
Needs more academic review

17. But wait!?

18. Async. Forward Secrecy Academic approaches
Hierarchical IBE (Canetti et al. 2003)
not considered in practice
Puncturable encryption (Green, Miers S&P 2015)

19. Remaining Challenges

20. Conversation Security Transport Privacy
Problem Areas
Trust Establishment
Long-term key verification
Conversation Security
Crypto stuff
Transport Privacy
Meta-data protection

21. Little progress in practice Usability and adoption implications
Transport Privacy
Hide metadata
Little progress in practice
Few tools adopted (mostly Tor)
Usability and adoption implications
Delays
Scalability issues
SPAM / Flood abuse (dealt in Pond)
Private contact discovery

22. Survey + Systematization Unconsidered approaches in both worlds
Takeaways
Survey + Systematization
Unconsidered approaches in both worlds
Appeal for academic analysis
Similar to SSL and Android research
Security analyses
Reach out to developers
Security proofs are not enough

23. Acknowledgements
Trevor Perrin
Henry Corrigan-Gibbs

24. Credits
Special thanks to all the people who made and released these awesome resources for free:
Presentation template by SlidesCarnival
Photographs by Unsplash & Death to the Stock Photo (license)

25. CSecurity is hard
Source: GPG for Journalists - Windows edition (Edward Snowden)

26. Idea: publicly verifiable logs No user action for verification
Transparency Logs
Idea: publicly verifiable logs
No user action for verification
Certificate Transparency
Privacy issues
Deployment issues
End-user behaviour
Gossiping not specified
CONIKs3
Blockchain solutions

27. Table 2 all sovled

28. Table 3

29. Asynchronous Forward Secrecy✗ ✗ ✗ ✗ ✗ ✗ ✗ ✗ ✗ ✗ ✗ ✗ ✗

30. Axolotl (in-the-wild)
Diffie-Hellman ratcheting
Symmetric ratchet
Symmetric ratchet
Diffie-Hellman ratcheting