1. Perspectives: Improving SSH- Style Host Authentication with Multi-Path Probing Analysis and Comments Gregory T. Hoffer CS7123 – Research Seminar (Dr. Qi Tian)

2. Overview  Project Description  Problem  Objective  Design  Security Analysis  Future Work

3. Project Description  Problem  SSL requires shared secret to be exchanged  Diffie-Hellman key exchange subject to MITM attack.

4. Project Description  SSL Certificate Acceptance (Tofu)

5. Project Description  Certificate Authority (CA)  List embedded in client  Certificate Revocation checks

6. Project Description  Problem Summary  Rely upon the user’s discretion to determine if unauthenticated key is valid  Key authentication is based upon “known good” list of trusted certs (“centralized trust brokers”), which have been shown to be insecure ( http://nakedsecurity.sophos.com/2011/03/24/fraudulent-certificates-issued- by-comodo-is-it-time-to-rethink-who-we-trust/ ) http://nakedsecurity.sophos.com/2011/03/24/fraudulent-certificates-issued- by-comodo-is-it-time-to-rethink-who-we-trust/  Certificate Revocation not always in use, and itself susceptible to attack or becoming stale.

7. Project Description  Objective  Create modular notary network  Tolerate internal failures  Tolerate compromises

8. Project Description  Design  Network of notaries  Each notary monitors and records keys requested/sent, cryptographically signed.  Multiple “Vantage Points” to provide fault tolerance, rigor against compromise of single (or few) notaries.  Data redundancy by “shadowed” copies of notary data.

9. Project Description Source: “With SSL, who can you really trust?”, 2011, Network World. (http://www.networkworld.c om/news/2011/081811- ssl-249874.html?page=2)http://www.networkworld.c om/news/2011/081811- ssl-249874.html?page=2

10. Security Analysis  MitM attacks provide client with false public key.  Assume attacks are either  Localized to a particular network scope, or  Of a limited duration  Data Redundancy helps clients detect malicious notaries  Bootstrapping the observations?  How to secure client operation (e.g. Plugins)?  How to manage notary trust?

11. Future Work Description Notary-Aware Services Additional Protocols DNSSEC Performance (Client, Server)

12. Conclusion  Perspectives represents an interesting class of security in an interesting deployment – network of notaries.  While addressing some key security problems of authenticating servers, it raises other questions of security of the system. Quis custodiet ipsos custodes?

13. Questions and Discussion  Any questions or comments?

14. References  Dan Wendlandt, David G. Andersen, and Adrian Perrig. 2008. Perspectives: improving SSH-style host authentication with multi-path probing. In USENIX 2008 Annual Technical Conference on Annual Technical Conference (ATC'08). USENIX Association, Berkeley, CA, USA, 321-334  J. Sunshine, S. Egelman, H. Almuhimedi, N. Atri, L. Cranor. 2009. Crying wolf: an empirical study of SSL warning effectiveness. In Proceedings of the 18th conference on USENIX security symposium (SSYM'09). USENIX Association, Berkeley, CA, USA, 399-416.