4<- index


5 CRL and CRL Extensions Profile

As discussed above, one goal of this X.509 v2 CRL profile is to foster the creation of an interoperable and reusable Internet PKI. To achieve this goal, guidelines for the use of extensions are specified, and some assumptions are made about the nature of information included in the CRL.

CRLs may be used in a wide range of applications and environments covering a broad spectrum of interoperability goals and an even broader spectrum of operational and assurance requirements. This profile establishes a common baseline for generic applications requiring broad interoperability. The profile defines a set of information that can be expected in every CRL. Also, the profile defines common locations within the CRL for frequently used attributes as well as common representations for these attributes.

CRL issuers issue CRLs. In general, the CRL issuer is the CA. CAs publish CRLs to provide status information about the certificates they issued. However, a CA may delegate this responsibility to another trusted authority. Whenever the CRL issuer is not the CA that issued the certificates, the CRL is referred to as an indirect CRL.

Each CRL has a particular scope. The CRL scope is the set of certificates that could appear on a given CRL. For example, the scope could be "all certificates issued by CA X", "all CA certificates issued by CA X", "all certificates issued by CA X that have been revoked for reasons of key compromise and CA compromise", or could be a set of certificates based on arbitrary local information, such as "all certificates issued to the NIST employees located in Boulder".

A complete CRL lists all unexpired certificates, within its scope, that have been revoked for one of the revocation reasons covered by the CRL scope. The CRL issuer MAY also generate delta CRLs. A delta CRL only lists those certificates, within its scope, whose revocation status has changed since the issuance of a referenced complete CRL. The referenced complete CRL is referred to as a base CRL. The scope of a delta CRL MUST be the same as the base CRL that it references.

This profile does not define any private Internet CRL extensions or CRL entry extensions.

Environments with additional or special purpose requirements may build on this profile or may replace it.

Conforming CAs are not required to issue CRLs if other revocation or certificate status mechanisms are provided. When CRLs are issued, the CRLs MUST be version 2 CRLs, include the date by which the next CRL will be issued in the nextUpdate field (section 5.1.2.5), include the CRL number extension (section 5.2.3), and include the authority key identifier extension (section 5.2.1). Conforming applications that support CRLs are REQUIRED to process both version 1 and version 2 complete CRLs that provide revocation information for all certificates issued by one CA. Conforming applications are NOT REQUIRED to support processing of delta CRLs, indirect CRLs, or CRLs with a scope other than all certificates issued by one CA.

5.1 CRL Fields

The X.509 v2 CRL syntax is as follows. For signature calculation, the data that is to be signed is ASN.1 DER encoded. ASN.1 DER encoding is a tag, length, value encoding system for each element.

CertificateList ::= SEQUENCE {

tbsCertList TBSCertList,
signatureAlgorithm AlgorithmIdentifier,
signatureValue BIT STRING }

TBSCertList ::= SEQUENCE {

version Version OPTIONAL, -- if present, MUST be v2
signature AlgorithmIdentifier,
issuer Name,
thisUpdate Time,
nextUpdate Time OPTIONAL,
revokedCertificates SEQUENCE OF SEQUENCE {

userCertificate CertificateSerialNumber,
revocationDate Time,
crlEntryExtensions Extensions OPTIONAL -- if present, MUST be v2 } OPTIONAL,

crlExtensions [0] EXPLICIT Extensions OPTIONAL -- if present, MUST be v2 }

-- Version, Time, CertificateSerialNumber, and Extensions -- are all defined in the ASN.1 in section 4.1

-- AlgorithmIdentifier is defined in section 4.1.1.2

The following items describe the use of the X.509 v2 CRL in the Internet PKI.

5.1.1 CertificateList Fields

The CertificateList is a SEQUENCE of three required fields. The fields are described in detail in the following subsections.

5.1.1.1 tbsCertList

The first field in the sequence is the tbsCertList. This field is itself a sequence containing the name of the issuer, issue date, issue date of the next list, the optional list of revoked certificates, and optional CRL extensions. When there are no revoked certificates, the revoked certificates list is absent. When one or more certificates are revoked, each entry on the revoked certificate list is defined by a sequence of user certificate serial number, revocation date, and optional CRL entry extensions.

5.1.1.2 signatureAlgorithm

The signatureAlgorithm field contains the algorithm identifier for the algorithm used by the CRL issuer to sign the CertificateList. The field is of type AlgorithmIdentifier, which is defined in section 4.1.1.2. [PKIXALGS] lists the supported algorithms for this specification, but other signature algorithms MAY also be supported.

This field MUST contain the same algorithm identifier as the signature field in the sequence tbsCertList (section 5.1.2.2).

5.1.1.3 signatureValue

The signatureValue field contains a digital signature computed upon the ASN.1 DER encoded tbsCertList. The ASN.1 DER encoded tbsCertList is used as the input to the signature function. This signature value is encoded as a BIT STRING and included in the CRL signatureValue field. The details of this process are specified for each of the supported algorithms in [PKIXALGS].

CAs that are also CRL issuers MAY use one private key to digitally sign certificates and CRLs, or MAY use separate private keys to digitally sign certificates and CRLs. When separate private keys are employed, each of the public keys associated with these private keys is placed in a separate certificate, one with the keyCertSign bit set in the key usage extension, and one with the cRLSign bit set in the key usage extension (section 4.2.1.3). When separate private keys are employed, certificates issued by the CA contain one authority key identifier, and the corresponding CRLs contain a different authority key identifier. The use of separate CA certificates for validation of certificate signatures and CRL signatures can offer improved security characteristics; however, it imposes a burden on applications, and it might limit interoperability. Many applications construct a certification path, and then validate the certification path (section 6). CRL checking in turn requires a separate certification path to be constructed and validated for the CA's CRL signature validation certificate. Applications that perform CRL checking MUST support certification path validation when certificates and CRLs are digitally signed with the same CA private key. These applications SHOULD support certification path validation when certificates and CRLs are digitally signed with different CA private keys.

5.1.2 Certificate List "To Be Signed"

The certificate list to be signed, or TBSCertList, is a sequence of required and optional fields. The required fields identify the CRL issuer, the algorithm used to sign the CRL, the date and time the CRL was issued, and the date and time by which the CRL issuer will issue the next CRL.

Optional fields include lists of revoked certificates and CRL extensions. The revoked certificate list is optional to support the case where a CA has not revoked any unexpired certificates that it has issued. The profile requires conforming CRL issuers to use the CRL number and authority key identifier CRL extensions in all CRLs issued.

5.1.2.1 Version

This optional field describes the version of the encoded CRL. When extensions are used, as required by this profile, this field MUST be present and MUST specify version 2 (the integer value is 1).

5.1.2.2 Signature

This field contains the algorithm identifier for the algorithm used to sign the CRL. [PKIXALGS] lists OIDs for the most popular signature algorithms used in the Internet PKI.

This field MUST contain the same algorithm identifier as the signatureAlgorithm field in the sequence CertificateList (section 5.1.1.2).

5.1.2.3 Issuer Name

The issuer name identifies the entity who has signed and issued the CRL. The issuer identity is carried in the issuer name field. Alternative name forms may also appear in the issuerAltName extension (section 5.2.2). The issuer name field MUST contain an X.500 distinguished name (DN). The issuer name field is defined as the X.501 type Name, and MUST follow the encoding rules for the issuer name field in the certificate (section 4.1.2.4).

5.1.2.4 This Update

This field indicates the issue date of this CRL. ThisUpdate may be encoded as UTCTime or GeneralizedTime.

CRL issuers conforming to this profile MUST encode thisUpdate as UTCTime for dates through the year 2049. CRL issuers conforming to this profile MUST encode thisUpdate as GeneralizedTime for dates in the year 2050 or later.

Where encoded as UTCTime, thisUpdate MUST be specified and interpreted as defined in section 4.1.2.5.1. Where encoded as GeneralizedTime, thisUpdate MUST be specified and interpreted as defined in section 4.1.2.5.2.

5.1.2.5 Next Update

This field indicates the date by which the next CRL will be issued. The next CRL could be issued before the indicated date, but it will not be issued any later than the indicated date. CRL issuers SHOULD issue CRLs with a nextUpdate time equal to or later than all previous CRLs. nextUpdate may be encoded as UTCTime or GeneralizedTime.

This profile requires inclusion of nextUpdate in all CRLs issued by conforming CRL issuers. Note that the ASN.1 syntax of TBSCertList describes this field as OPTIONAL, which is consistent with the ASN.1 structure defined in [X.509]. The behavior of clients processing CRLs which omit nextUpdate is not specified by this profile.

CRL issuers conforming to this profile MUST encode nextUpdate as UTCTime for dates through the year 2049. CRL issuers conforming to this profile MUST encode nextUpdate as GeneralizedTime for dates in the year 2050 or later.

Where encoded as UTCTime, nextUpdate MUST be specified and interpreted as defined in section 4.1.2.5.1. Where encoded as GeneralizedTime, nextUpdate MUST be specified and interpreted as defined in section 4.1.2.5.2.

5.1.2.6 Revoked Certificates

When there are no revoked certificates, the revoked certificates list MUST be absent. Otherwise, revoked certificates are listed by their serial numbers. Certificates revoked by the CA are uniquely identified by the certificate serial number. The date on which the revocation occurred is specified. The time for revocationDate MUST be expressed as described in section 5.1.2.4. Additional information may be supplied in CRL entry extensions; CRL entry extensions are discussed in section 5.3.

5.1.2.7 Extensions

This field may only appear if the version is 2 (section 5.1.2.1). If present, this field is a sequence of one or more CRL extensions. CRL extensions are discussed in section 5.2.

5.2 CRL Extensions

The extensions defined by ANSI X9, ISO/IEC, and ITU-T for X.509 v2 CRLs [X.509] [X9.55] provide methods for associating additional attributes with CRLs. The X.509 v2 CRL format also allows communities to define private extensions to carry information unique to those communities. Each extension in a CRL may be designated as critical or non-critical. A CRL validation MUST fail if it encounters a critical extension which it does not know how to process. However, an unrecognized non-critical extension may be ignored. The following subsections present those extensions used within Internet CRLs. Communities may elect to include extensions in CRLs which are not defined in this specification. However, caution should be exercised in adopting any critical extensions in CRLs which might be used in a general context.

Conforming CRL issuers are REQUIRED to include the authority key identifier (section 5.2.1) and the CRL number (section 5.2.3) extensions in all CRLs issued.

5.2.1 Authority Key Identifier

The authority key identifier extension provides a means of identifying the public key corresponding to the private key used to sign a CRL. The identification can be based on either the key identifier (the subject key identifier in the CRL signer's certificate) or on the issuer name and serial number. This extension is especially useful where an issuer has more than one signing key, either due to multiple concurrent key pairs or due to changeover.

Conforming CRL issuers MUST use the key identifier method, and MUST include this extension in all CRLs issued.

The syntax for this CRL extension is defined in section 4.2.1.1.

5.2.2 Issuer Alternative Name

The issuer alternative names extension allows additional identities to be associated with the issuer of the CRL. Defined options include an rfc822 name (electronic mail address), a DNS name, an IP address, and a URI. Multiple instances of a name and multiple name forms may be included. Whenever such identities are used, the issuer alternative name extension MUST be used; however, a DNS name MAY be represented in the issuer field using the domainComponent attribute as described in section 4.1.2.4.

The issuerAltName extension SHOULD NOT be marked critical.

The OID and syntax for this CRL extension are defined in section 4.2.1.8.

5.2.3 CRL Number

The CRL number is a non-critical CRL extension which conveys a monotonically increasing sequence number for a given CRL scope and CRL issuer. This extension allows users to easily determine when a particular CRL supersedes another CRL. CRL numbers also support the identification of complementary complete CRLs and delta CRLs. CRL issuers conforming to this profile MUST include this extension in all CRLs.

If a CRL issuer generates delta CRLs in addition to complete CRLs for a given scope, the complete CRLs and delta CRLs MUST share one numbering sequence. If a delta CRL and a complete CRL that cover the same scope are issued at the same time, they MUST have the same CRL number and provide the same revocation information. That is, the combination of the delta CRL and an acceptable complete CRL MUST provide the same revocation information as the simultaneously issued complete CRL.

If a CRL issuer generates two CRLs (two complete CRLs, two delta CRLs, or a complete CRL and a delta CRL) for the same scope at different times, the two CRLs MUST NOT have the same CRL number. That is, if the this update field (section 5.1.2.4) in the two CRLs are not identical, the CRL numbers MUST be different.

Given the requirements above, CRL numbers can be expected to contain long integers. CRL verifiers MUST be able to handle CRLNumber values up to 20 octets. Conformant CRL issuers MUST NOT use CRLNumber values longer than 20 octets.

id-ce-cRLNumber OBJECT IDENTIFIER ::= { id-ce 20 }

CRLNumber ::= INTEGER (0..MAX)

5.2.4 Delta CRL Indicator

The delta CRL indicator is a critical CRL extension that identifies a CRL as being a delta CRL. Delta CRLs contain updates to revocation information previously distributed, rather than all the information that would appear in a complete CRL. The use of delta CRLs can significantly reduce network load and processing time in some environments. Delta CRLs are generally smaller than the CRLs they update, so applications that obtain delta CRLs consume less network bandwidth than applications that obtain the corresponding complete CRLs. Applications which store revocation information in a format other than the CRL structure can add new revocation information to the local database without reprocessing information.

The delta CRL indicator extension contains the single value of type BaseCRLNumber. The CRL number identifies the CRL, complete for a given scope, that was used as the starting point in the generation of this delta CRL. A conforming CRL issuer MUST publish the referenced base CRL as a complete CRL. The delta CRL contains all updates to the revocation status for that same scope. The combination of a delta CRL plus the referenced base CRL is equivalent to a complete CRL, for the applicable scope, at the time of publication of the delta CRL.

When a conforming CRL issuer generates a delta CRL, the delta CRL MUST include a critical delta CRL indicator extension.

When a delta CRL is issued, it MUST cover the same set of reasons and the same set of certificates that were covered by the base CRL it references. That is, the scope of the delta CRL MUST be the same as the scope of the complete CRL referenced as the base. The referenced base CRL and the delta CRL MUST omit the issuing distribution point extension or contain identical issuing distribution point extensions. Further, the CRL issuer MUST use the same private key to sign the delta CRL and any complete CRL that it can be used to update.

An application that supports delta CRLs can construct a CRL that is complete for a given scope by combining a delta CRL for that scope with either an issued CRL that is complete for that scope or a locally constructed CRL that is complete for that scope.

When a delta CRL is combined with a complete CRL or a locally constructed CRL, the resulting locally constructed CRL has the CRL number specified in the CRL number extension found in the delta CRL used in its construction. In addition, the resulting locally constructed CRL has the thisUpdate and nextUpdate times specified in the corresponding fields of the delta CRL used in its construction. In addition, the locally constructed CRL inherits the issuing distribution point from the delta CRL.

A complete CRL and a delta CRL MAY be combined if the following four conditions are satisfied:

(a) The complete CRL and delta CRL have the same issuer.

(b) The complete CRL and delta CRL have the same scope. The two CRLs have the same scope if either of the following conditions are met:

(1) The issuingDistributionPoint extension is omitted from both the complete CRL and the delta CRL.

(2) The issuingDistributionPoint extension is present in both the complete CRL and the delta CRL, and the values for each of the fields in the extensions are the same in both CRLs.

(c) The CRL number of the complete CRL is equal to or greater than the BaseCRLNumber specified in the delta CRL. That is, the complete CRL contains (at a minimum) all the revocation information held by the referenced base CRL.

(d) The CRL number of the complete CRL is less than the CRL number of the delta CRL. That is, the delta CRL follows the complete CRL in the numbering sequence.

CRL issuers MUST ensure that the combination of a delta CRL and any appropriate complete CRL accurately reflects the current revocation status. The CRL issuer MUST include an entry in the delta CRL for each certificate within the scope of the delta CRL whose status has changed since the generation of the referenced base CRL:

(a) If the certificate is revoked for a reason included in the scope of the CRL, list the certificate as revoked.

(b) If the certificate is valid and was listed on the referenced base CRL or any subsequent CRL with reason code certificateHold, and the reason code certificateHold is included in the scope of the CRL, list the certificate with the reason code removeFromCRL.

(c) If the certificate is revoked for a reason outside the scope of the CRL, but the certificate was listed on the referenced base CRL or any subsequent CRL with a reason code included in the scope of this CRL, list the certificate as revoked but omit the reason code.

(d) If the certificate is revoked for a reason outside the scope of the CRL and the certificate was neither listed on the referenced base CRL nor any subsequent CRL with a reason code included in the scope of this CRL, do not list the certificate on this CRL.

The status of a certificate is considered to have changed if it is revoked, placed on hold, released from hold, or if its revocation reason changes.

It is appropriate to list a certificate with reason code removeFromCRL on a delta CRL even if the certificate was not on hold in the referenced base CRL. If the certificate was placed on hold in any CRL issued after the base but before this delta CRL and then released from hold, it MUST be listed on the delta CRL with revocation reason removeFromCRL.

A CRL issuer MAY optionally list a certificate on a delta CRL with reason code removeFromCRL if the notAfter time specified in the certificate precedes the thisUpdate time specified in the delta CRL and the certificate was listed on the referenced base CRL or in any CRL issued after the base but before this delta CRL.

If a certificate revocation notice first appears on a delta CRL, then it is possible for the certificate validity period to expire before the next complete CRL for the same scope is issued. In this case, the revocation notice MUST be included in all subsequent delta CRLs until the revocation notice is included on at least one explicitly issued complete CRL for this scope.

An application that supports delta CRLs MUST be able to construct a current complete CRL by combining a previously issued complete CRL and the most current delta CRL. An application that supports delta CRLs MAY also be able to construct a current complete CRL by combining a previously locally constructed complete CRL and the current delta CRL. A delta CRL is considered to be the current one if the current time is between the times contained in the thisUpdate and nextUpdate fields. Under some circumstances, the CRL issuer may publish one or more delta CRLs before indicated by the nextUpdate field. If more than one current delta CRL for a given scope is encountered, the application SHOULD consider the one with the latest value in thisUpdate to be the most current one.

id-ce-deltaCRLIndicator OBJECT IDENTIFIER ::= { id-ce 27 }

BaseCRLNumber ::= CRLNumber

5.2.5 Issuing Distribution Point

The issuing distribution point is a critical CRL extension that identifies the CRL distribution point and scope for a particular CRL, and it indicates whether the CRL covers revocation for end entity certificates only, CA certificates only, attribute certificates only,

or a limited set of reason codes. Although the extension is critical, conforming implementations are not required to support this extension.

The CRL is signed using the CRL issuer's private key. CRL Distribution Points do not have their own key pairs. If the CRL is stored in the X.500 Directory, it is stored in the Directory entry corresponding to the CRL distribution point, which may be different than the Directory entry of the CRL issuer.

The reason codes associated with a distribution point MUST be specified in onlySomeReasons. If onlySomeReasons does not appear, the distribution point MUST contain revocations for all reason codes. CAs may use CRL distribution points to partition the CRL on the basis of compromise and routine revocation. In this case, the revocations with reason code keyCompromise (1), cACompromise (2), and aACompromise (8) appear in one distribution point, and the revocations with other reason codes appear in another distribution point.

If the distributionPoint field is present and contains a URI, the following semantics MUST be assumed: the object is a pointer to the most current CRL issued by this CRL issuer. The URI schemes ftp, http, mailto [RFC1738] and ldap [RFC1778] are defined for this purpose. The URI MUST be an absolute pathname, not a relative pathname, and MUST specify the host.

If the distributionPoint field is absent, the CRL MUST contain entries for all revoked unexpired certificates issued by the CRL issuer, if any, within the scope of the CRL.

The CRL issuer MUST assert the indirectCRL boolean, if the scope of the CRL includes certificates issued by authorities other than the CRL issuer. The authority responsible for each entry is indicated by the certificate issuer CRL entry extension (section 5.3.4).

id-ce-issuingDistributionPoint OBJECT IDENTIFIER ::= { id-ce 28 }

issuingDistributionPoint ::= SEQUENCE {

distributionPoint [0] DistributionPointName OPTIONAL,
onlyContainsUserCerts [1] BOOLEAN DEFAULT FALSE,
onlyContainsCACerts [2] BOOLEAN DEFAULT FALSE,
onlySomeReasons [3] ReasonFlags OPTIONAL,
indirectCRL [4] BOOLEAN DEFAULT FALSE,
onlyContainsAttributeCerts [5] BOOLEAN DEFAULT FALSE }

5.2.6 Freshest CRL (a.k.a. Delta CRL Distribution Point)

The freshest CRL extension identifies how delta CRL information for this complete CRL is obtained. The extension MUST be non-critical. This extension MUST NOT appear in delta CRLs.

The same syntax is used for this extension as the cRLDistributionPoints certificate extension, and is described in section 4.2.1.14. However, only the distribution point field is meaningful in this context. The reasons and CRLIssuer fields MUST be omitted from this CRL extension.

Each distribution point name provides the location at which a delta CRL for this complete CRL can be found. The scope of these delta CRLs MUST be the same as the scope of this complete CRL. The contents of this CRL extension are only used to locate delta CRLs; the contents are not used to validate the CRL or the referenced delta CRLs. The encoding conventions defined for distribution points in section 4.2.1.14 apply to this extension.

id-ce-freshestCRL OBJECT IDENTIFIER ::= { id-ce 46 }

FreshestCRL ::= CRLDistributionPoints

5.3 CRL Entry Extensions

The CRL entry extensions defined by ISO/IEC, ITU-T, and ANSI X9 for X.509 v2 CRLs provide methods for associating additional attributes with CRL entries [X.509] [X9.55]. The X.509 v2 CRL format also allows communities to define private CRL entry extensions to carry information unique to those communities. Each extension in a CRL entry may be designated as critical or non-critical. A CRL validation MUST fail if it encounters a critical CRL entry extension which it does not know how to process. However, an unrecognized non- critical CRL entry extension may be ignored. The following subsections present recommended extensions used within Internet CRL entries and standard locations for information. Communities may elect to use additional CRL entry extensions; however, caution should be exercised in adopting any critical extensions in CRL entries which might be used in a general context.

All CRL entry extensions used in this specification are non-critical. Support for these extensions is optional for conforming CRL issuers and applications. However, CRL issuers SHOULD include reason codes (section 5.3.1) and invalidity dates (section 5.3.3) whenever this information is available.

5.3.1 Reason Code

The reasonCode is a non-critical CRL entry extension that identifies the reason for the certificate revocation. CRL issuers are strongly encouraged to include meaningful reason codes in CRL entries; however, the reason code CRL entry extension SHOULD be absent instead of using the unspecified (0) reasonCode value.

id-ce-cRLReason OBJECT IDENTIFIER ::= { id-ce 21 }

-- reasonCode ::= { CRLReason }

CRLReason ::= ENUMERATED {

unspecified (0),
keyCompromise (1),
cACompromise (2),
affiliationChanged (3),
superseded (4),
cessationOfOperation (5),
certificateHold (6),
removeFromCRL (8),
privilegeWithdrawn (9),
aACompromise (10) }

5.3.2 Hold Instruction Code

The hold instruction code is a non-critical CRL entry extension that provides a registered instruction identifier which indicates the action to be taken after encountering a certificate that has been placed on hold.

id-ce-holdInstructionCode OBJECT IDENTIFIER ::= { id-ce 23 }

holdInstructionCode ::= OBJECT IDENTIFIER

The following instruction codes have been defined. Conforming applications that process this extension MUST recognize the following instruction codes.

holdInstruction OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) x9-57(10040) 2 }

id-holdinstruction-none OBJECT IDENTIFIER ::= {holdInstruction 1}
id-holdinstruction-callissuer OBJECT IDENTIFIER ::= {holdInstruction 2}
id-holdinstruction-reject OBJECT IDENTIFIER ::= {holdInstruction 3}

Conforming applications which encounter an id-holdinstruction- callissuer MUST call the certificate issuer or reject the certificate. Conforming applications which encounter an id- holdinstruction-reject MUST reject the certificate. The hold instruction id-holdinstruction-none is semantically equivalent to the absence of a holdInstructionCode, and its use is strongly deprecated for the Internet PKI.

5.3.3 Invalidity Date

The invalidity date is a non-critical CRL entry extension that provides the date on which it is known or suspected that the private key was compromised or that the certificate otherwise became invalid. This date may be earlier than the revocation date in the CRL entry, which is the date at which the CA processed the revocation. When a revocation is first posted by a CRL issuer in a CRL, the invalidity date may precede the date of issue of earlier CRLs, but the revocation date SHOULD NOT precede the date of issue of earlier CRLs. Whenever this information is available, CRL issuers are strongly encouraged to share it with CRL users.

The GeneralizedTime values included in this field MUST be expressed in Greenwich Mean Time (Zulu), and MUST be specified and interpreted as defined in section 4.1.2.5.2.

id-ce-invalidityDate OBJECT IDENTIFIER ::= { id-ce 24 }

invalidityDate ::= GeneralizedTime

5.3.4 Certificate Issuer

This CRL entry extension identifies the certificate issuer associated with an entry in an indirect CRL, that is, a CRL that has the indirectCRL indicator set in its issuing distribution point extension. If this extension is not present on the first entry in an indirect CRL, the certificate issuer defaults to the CRL issuer. On subsequent entries in an indirect CRL, if this extension is not present, the certificate issuer for the entry is the same as that for the preceding entry. This field is defined as follows:

id-ce-certificateIssuer OBJECT IDENTIFIER ::= { id-ce 29 }

certificateIssuer ::= GeneralNames

If used by conforming CRL issuers, this extension MUST always be critical. If an implementation ignored this extension it could not correctly attribute CRL entries to certificates. This specification RECOMMENDS that implementations recognize this extension.


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