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Perspectives: Improving SSH-Style Host Authentication with Multi-Path ProbingAnalysis and CommentsGregory T. Hoffer
CS7123 – Research Seminar (Dr. Qi Tian)
Overview
Project Description Problem Objective Design
Security Analysis Future Work
Project Description
Problem SSL requires shared secret to be exchanged Diffie-Hellman key exchange subject to
MITM attack.
Project Description
SSL Certificate Acceptance (Tofu)
Project Description
Certificate Authority (CA) List embedded in client Certificate Revocation checks
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/
) Certificate Revocation not always in use,
and itself susceptible to attack or becoming stale.
Project Description
Objective Create modular notary network Tolerate internal failures Tolerate compromises
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.
Project Description
Source: “With SSL, who can you really trust?”, 2011, Network World. (http://www.networkworld.com/news/2011/081811-ssl-249874.html?page=2)
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?
Future Work
Description
Notary-Aware Services
Additional Protocols
DNSSEC
Performance (Client, Server)
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?
Questions and Discussion
Any questions or comments?
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.