1. PKI 202 – Architecture Models and CRLs
Aman Hardikar

2. Agenda
• Architecture Models
• Subordinate
• Cross certified mesh
• Bridge
• Trusted list
• Revocation
• CRL
• OCSP

3. Overview
Available at www.amanhardikar.com/mindmaps.html
Mindmap:

4. Topics Today

5. PKI Trust Models
The fundamental purpose of PKI is to represent
the trust relationship between participating
parties.
The verifier verifies the chain of trust.
Four models exist:
• Subordinate Hierarchy
• Cross Certified Mesh
• Bridge CA
• Trusted List

6. Subordinate Hierarchy
• Two or more CAs in a hierarchical relationship
• Good for single enterprise applications
• Hard to implement between enterprises

7. Cross Certified Mesh
• Each internal CA signs the other PKI’s public verification keys
• Good for dynamically changing enterprise PKI applications
• Scalability is a major issue. Need to support n(n-1) cross certifications

8. Bridge CA
• Only the Root CAs participate in the cross certification
• Solves the issues with the mesh model

9. Trusted List
• Uses a set of publicly trusted root
certificates
• Ex: Internet Browsers

10. Traditional CRLs
Relying party checks the certificate against the latest published
CRLs
Disadvantage:
Long CRLs and the number the users directly proportional to the
performance of the network.

11. Modified CRLs
• Overissued CRLs
• Segmented CRLs
• Delta CRLs
• Sliding window (overissued delta) CRLs

12. OCSP
Online Certificate Status Protocol
• Client – Server model
• Client requests status of a certificate
• Server sends a signed response back
• Advantages
• Very small request and response
• Disadvantages
• All responses need to be signed increasing the load on the server
• Clients must be online/connected to check the status

13. SSLAuditor3 Preview
Report generation code needs few fixes

14. Next Presentations
PKI Applications
SSL
S/MIME
PGP
IKE
SSLAuditor3 demo
PKI Architecture Weakness / Audit
Architecture Weaknesses
Auditing
Mitigation Procedure
Best Practices

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