Appendix B. Defaults, Constraints, and Extensions for Certificates and CRLs
468
• The object identifier (OID) for the extension. This identifier uniquely identifies the extension. It
also determines the ASN.1 type of value in the value field and how the value is interpreted. When
an extension appears in a CRL, the OID appears as the extension ID field (
extnID
) and the
corresponding ASN.1 encoded structure appears as the value of the octet string (
extnValue
);
examples are shown in
Example B.3, “Sample Pretty-Print Certificate Extensions”
.
• A flag or Boolean field called
critical
.
The
true
or
false
value assigned to this field indicates whether the extension is critical or
noncritical to the CRL.
• If the extension is critical and the CRL is sent to an application that does not understand the
extension based on the extension's ID, the application must reject the CRL.
• If the extension is not critical and the CRL is sent to an application that does not understand the
extension based on the extension's ID, the application can ignore the extension and accept the
CRL.
• An octet string containing the DER encoding of the value of the extension.
The application receiving the CRL checks the extension ID to determine if it can recognize the ID. If it
can, it uses the extension ID to determine the type of value used.
B.4.1.2. Sample CRL and CRL Entry Extensions
The following is an example of an X.509 CRL version 2 extension. The Certificate System can display
CRLs in readable pretty-print format, as shown here. As shown in the example, CRL extensions
appear in sequence and only one instance of a particular extension may appear per CRL; for example,
a CRL may contain only one Authority Key Identifier extension. However, CRL-entry extensions
appear in appropriate entries in the CRL.
Certificate Revocation List:
Data:
Version: v2
Signature Algorithm: SHA1withRSA - 1.2.840.113549.1.1.5
Issuer: CN=Certificate Authority,O=Example Domain
This Update: Wednesday, July 29, 2009 8:59:48 AM GMT-08:00
Next Update: Friday, July 31, 2009 8:59:48 AM GMT-08:00
Revoked Certificates: 1-3 of 3
Serial Number: 0x11
Revocation Date: Thursday, July 23, 2009 10:07:15 AM GMT-08:00
Extensions:
Identifier: Revocation Reason - 2.5.29.21
Critical: no
Reason: Privilege_Withdrawn
Serial Number: 0x1A
Revocation Date: Wednesday, July 29, 2009 8:50:11 AM GMT-08:00
Extensions:
Identifier: Revocation Reason - 2.5.29.21
Critical: no
Reason: Certificate_Hold
Identifier: Invalidity Date - 2.5.29.24
Critical: no
Invalidity Date: Sun Jul 26 23:00:00 GMT-08:00 2009
Serial Number: 0x19
Revocation Date: Wednesday, July 29, 2009 8:50:49 AM GMT-08:00
Extensions:
Identifier: Revocation Reason - 2.5.29.21
Summary of Contents for CERTIFICATE SYSTEM 8.0 - ADMINISTRATION
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