1. Document update - what has happened since GGF11
OCSP Requirements
Document update - what has happened since GGF11

2. Refreshener OCSP = Online Certificate Status Protocol (RFC2560)
“Removes” burden of wide-area CRL distribution and update
Clients still have to do path validation!
Clients still have to know about all CAs!
Reasonably lightweight request/response protocol carried over HTTP(S)

3. Trust model alternatives supported by the RFC
CA signs responses
Authorized Responder
Dedicated OCSP signing key certified by issuing CA
Trusted Responder
Explicit, configured trust
We propose to use a combination of #2 and #3, for a variety of reasons

4. Our OCSP service architecture
site/organization boundary CA
CRL cache CA
OCSP client CA
Trusted Responder
OCSP
client
Trusted Responder
Authorized Responder
Authorized Responder

5. Revocation status of OCSP responder?
Don’t
OCSP-no-check extension
Shortlived certificates
Can be applied to any frequently validated certificate!

6. CA requirements
SHOULD include service locator of authorized responder(s) in all issued certificates
SHOULD certify authorized responders with ocsp-nocheck and OCSPSigning extensions
SHOULD make sure authorized responders are updated immediately after e.g. CRL update.

7. Client Requirements Network connectivity Response caching Nonce
Duh... but a strong motivation for trusted responder at site/org perimeter
Response caching
SHOULD
If used, MUST be possible to limit
Nonce
SHOULD NOT

8. Trusted Responder architecture (NON-normative)
Other Responder
CRL cache
(Re-)sign external responses?
OCSP cache
OCSP Responder
OCSP client
Responder interface
request

9. Server requirements Signature key protection
RECOMMEND use of HW
SHOULD support for handling multiple signature certificates
One per CA (Authorized responder)
Transponder mode
Do not resign responses, just forward them
Preserves Authorized responder signature

10. Handling errors and “Unknown” responses
Not covered by RFC
Our suggestion:
Interpret Unknown or error as “try next revocation source”
If no next, treat it as Revoked with permission onHold
... unless otherwise configured (avoid DoS)

11. Responder(s) location discovery
Via Service Locator (AIA extension)
MUST
Via Local configuration
SHOULD be able to handle per-issuer granularity and provide a default
Local configuration has precedence

12. Revocation sources
MUST be able to handle both locally cached CRLs and querying OCSP responders
Configurable which one to prefer over the other
Different deployment scenarios

13. Next steps
Open issues

14. Hierarchies CA Sub CA Result: Good Signature: ... CertChain: R1: CA
Responder
Sub CA
R2: SCA Responder
Result: Good Signature: ... CertChain:
Subject=R2
Issuer=SCA ocsp-nocheck
Subject=SCA
Issuer=CA AIA={R1}
OCSP
client
Trusted Responder
Subject=John
Issuer=SCA AIA={R2}
Issuer=SCA Serial#=1234 AIA={R2}

15. When should a trusted responder resign an OCSP response?
Always
Only if response is from non-authorized responder
Never

16. HTTP or HTTPS? Responses are signed Error messages are not
Suggestion: HTTP