Certificate Revocation Serge Egelman
Introduction What is revocation? Why do we need it? What is currently being done?
Huh? Certificates Are: Identity Personal Corporate Financial Overall Security
Why Revoke? Key Compromise Forgotten Passphrase Lost Private Key Stale Keys “PKI is only as secure as the revocation mechanism”
Current Standard Certificate Revocation Lists (CRLs) Serial Numbers PEM and DER Expiration Date Next Update Date CA Signed Should Be Publically Available.
Obtaining CRLs
Certificate Revocation List (CRL): Version 1 (0x0) Signature Algorithm: md5WithRSAEncryption Issuer: /C=US/O=RSA Data Security, Inc./OU=Secure Server Certification Authority Last Update: Jan 22 11:00: GMT Next Update: Feb 5 11:00: GMT Revoked Certificates: Serial Number: E0F79E9034FDD3D176DBB83A05 Revocation Date: Apr 2 15:03: GMT Serial Number: E434C44813CFCA5A829BF Revocation Date: Sep 17 23:48: GMT Serial Number: 0104C6A B92A015D F Revocation Date: May 15 22:03: GMT
What Are The Problems? CDP Not Specified! CDP Optional! Next Update in Two Weeks!
Among All CAs! CDP Protocols: CA NameCDP Protocol EntrustHTTP/LDAP GeoTrustHTTP GlobalSignHTTP GTE CyberTrust HTTP IPSCAHTTP Thawte VerisignHTTP
Among All CAs! CRL Lifecycles: CA NameCRL Lifecycle EntrustDaily GeoTrust10 Days GlobalSign30 Days GTE CyberTrust6 Months IPSCA30 Days Thawte30 Days Verisign14 Days
CA Market Share
There Must Be Another Way! Online Certificate Status Protocol (RFC 2560) Real-Time Three Responses Burden Moved to Server
OCSP OCSP Servers: CA Run CA Delegated Trusted Third Parties Client Knows Server Address Client Sends Serial Number Server Sends Signed Response
The Next Problem Knowing Location of Server! System Is Useless So What Can We Do?
A Solution The DNS System Referrals Client Only Needs Address of Any Server! Authority is Delegated The Service Locator Extension Specifics Undefined Not Currently Being Used Signed Response Local Responder or CA Key
So What? OCSP Can Mimic DNS Local Responders Authoritative Responders Root OCSP Servers Nothing Known About Authoritative Responder!
Key Points Every PKI Needs Revocation! CRLs Bad! OCSP Good!
Conclusion Terrorist, Terrorist, Terrorist 9/11, 9/11 God Bless America
References Ron Rivest, Can We Eliminate Certificate Revocation Lists?, Financial Cryptography, Patrick McDaniel and Aviel Rubin, A Reponse to “Can We Eliminate Certificate Revocation Lists?,” Financial Cryptography, Serge Egelman, Josh Zaritsky, and Anita Jones, Improved Certificate Revocation with OCSP. M. Myers, R. Ankney, A. Malpani, S. Galperin, and C. Adams, X.509 Internet Public Key Infrastructure: Online Certificate Status Protocol (OCSP), IETF RFC R. Housley, W. Polk, W. Ford, and D. Solo, Internet X.509 Public Key Infrastructure Certificate and CRL Profile, IETF RFC 2459.
Questions?