Appendix B. Defaults, Constraints, and Extensions for Certificates and CRLs
464
Table B.31, “Certificate Uses and Corresponding Key Usage Bits”
summarizes the guidelines for
typical certificate uses.
If the
keyUsage
extension is present and marked critical, then it is used to enforce the usage of the
certificate and key. The extension is used to limit the usage of a key; if the extension is not present or
not critical, all types of usage are allowed.
If the
keyUsage
extension is present, critical or not, it is used to select from multiple certificates for a
given operation. For example, it is used to distinguish separate signing and encryption certificates for
users who have separate certificates and key pairs for operations.
OID
2.5.29.15
Criticality
This extension may be critical or noncritical. PKIX Part 1 recommends that it should be marked critical
if it is used.
Purpose of Certificate
Required Key Usage Bit
CA Signing
• keyCertSign
• cRLSign
SSL Client
digitalSignature
SSL Server
keyEncipherment
S/MIME Signing
digitalSignature
S/MIME Encryption
keyEncipherment
Certificate Signing
keyCertSign
Object Signing
digitalSignature
Table B.31. Certificate Uses and Corresponding Key Usage Bits
B.3.9. nameConstraints
This extension, which can used in CA certificates only, defines a name space within which all subject
names in subsequent certificates in a certification path must be located.
OID
2.5.29.30
Criticality
PKIX Part 1 requires that this extension be marked critical.
B.3.10. OCSPNocheck
The extension is meant to be included in an OCSP signing certificate. The extension tells an OCSP
client that the signing certificate can be trusted without querying the OCSP responder (since the reply
would again be signed by the OCSP responder, and the client would again request the validity status
Summary of Contents for CERTIFICATE SYSTEM 8.0 - ADMINISTRATION
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