3<- index


4 Certificate and Certificate Extensions Profile

This section presents a profile for public key certificates that will foster interoperability and a reusable PKI. This section is based upon the X.509 v3 certificate format and the standard certificate extensions defined in [X.509]. The ISO/IEC and ITU-T documents use the 1997 version of ASN.1; while this document uses the 1988 ASN.1 syntax, the encoded certificate and standard extensions are equivalent. This section also defines private extensions required to support a PKI for the Internet community.

Certificates may be used in a wide range of applications and environments covering a broad spectrum of interoperability goals and a broader spectrum of operational and assurance requirements. The goal of this document is to establish a common baseline for generic applications requiring broad interoperability and limited special purpose requirements. In particular, the emphasis will be on supporting the use of X.509 v3 certificates for informal Internet electronic mail, IPsec, and WWW applications.

4.1 Basic Certificate Fields

The X.509 v3 certificate basic syntax is as follows. For signature calculation, the data that is to be signed is encoded using the ASN.1 distinguished encoding rules (DER) [X.690]. ASN.1 DER encoding is a tag, length, value encoding system for each element.

Certificate ::= SEQUENCE {

tbsCertificate TBSCertificate,
signatureAlgorithm AlgorithmIdentifier,
signatureValue BIT STRING }

TBSCertificate ::= SEQUENCE {

version [0] EXPLICIT Version DEFAULT v1,
serialNumber CertificateSerialNumber,
signature AlgorithmIdentifier,
issuer Name,
validity Validity,
subject Name,
subjectPublicKeyInfo SubjectPublicKeyInfo,
issuerUniqueID [1] IMPLICIT UniqueIdentifier OPTIONAL, -- If present, version MUST be v2 or v3
subjectUniqueID [2] IMPLICIT UniqueIdentifier OPTIONAL, -- If present, version MUST be v2 or v3
extensions [3] EXPLICIT Extensions OPTIONAL -- If present, version MUST be v3 }

Version ::= INTEGER { v1(0), v2(1), v3(2) }

CertificateSerialNumber ::= INTEGER

Validity ::= SEQUENCE {

notBefore Time, notAfter Time }

Time ::= CHOICE {

utcTime UTCTime, generalTime GeneralizedTime }

UniqueIdentifier ::= BIT STRING

SubjectPublicKeyInfo ::= SEQUENCE {

algorithm AlgorithmIdentifier, subjectPublicKey BIT STRING }

Extensions ::= SEQUENCE SIZE (1..MAX) OF Extension

Extension ::= SEQUENCE {

extnID OBJECT IDENTIFIER,
critical BOOLEAN DEFAULT FALSE,
extnValue OCTET STRING }

The following items describe the X.509 v3 certificate for use in the Internet.

4.1.1 Certificate Fields

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

4.1.1.1 tbsCertificate

The field contains the names of the subject and issuer, a public key associated with the subject, a validity period, and other associated information. The fields are described in detail in section 4.1.2; the tbsCertificate usually includes extensions which are described in section 4.2.

4.1.1.2 signatureAlgorithm

The signatureAlgorithm field contains the identifier for the cryptographic algorithm used by the CA to sign this certificate. [PKIXALGS] lists supported signature algorithms, but other signature algorithms MAY also be supported.

An algorithm identifier is defined by the following ASN.1 structure:

AlgorithmIdentifier ::= SEQUENCE {

algorithm OBJECT IDENTIFIER,
parameters ANY DEFINED BY algorithm OPTIONAL }

The algorithm identifier is used to identify a cryptographic algorithm. The OBJECT IDENTIFIER component identifies the algorithm (such as DSA with SHA-1). The contents of the optional parameters field will vary according to the algorithm identified.

This field MUST contain the same algorithm identifier as the signature field in the sequence tbsCertificate (section 4.1.2.3).

4.1.1.3 signatureValue

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

By generating this signature, a CA certifies the validity of the information in the tbsCertificate field. In particular, the CA certifies the binding between the public key material and the subject of the certificate.

4.1.2 TBSCertificate

The sequence TBSCertificate contains information associated with the subject of the certificate and the CA who issued it. Every TBSCertificate contains the names of the subject and issuer, a public key associated with the subject, a validity period, a version number, and a serial number; some MAY contain optional unique identifier fields. The remainder of this section describes the syntax and semantics of these fields. A TBSCertificate usually includes extensions. Extensions for the Internet PKI are described in Section 4.2.

4.1.2.1 Version

This field describes the version of the encoded certificate. When extensions are used, as expected in this profile, version MUST be 3 (value is 2). If no extensions are present, but a UniqueIdentifier is present, the version SHOULD be 2 (value is 1); however version MAY be 3. If only basic fields are present, the version SHOULD be 1 (the value is omitted from the certificate as the default value); however the version MAY be 2 or 3.

Implementations SHOULD be prepared to accept any version certificate. At a minimum, conforming implementations MUST recognize version 3 certificates.

Generation of version 2 certificates is not expected by implementations based on this profile.

4.1.2.2 Serial number

The serial number MUST be a positive integer assigned by the CA to each certificate. It MUST be unique for each certificate issued by a given CA (i.e., the issuer name and serial number identify a unique certificate). CAs MUST force the serialNumber to be a non-negative integer.

Given the uniqueness requirements above, serial numbers can be expected to contain long integers. Certificate users MUST be able to handle serialNumber values up to 20 octets. Conformant CAs MUST NOT use serialNumber values longer than 20 octets.

Note: Non-conforming CAs may issue certificates with serial numbers that are negative, or zero. Certificate users SHOULD be prepared to gracefully handle such certificates.

4.1.2.3 Signature

This field contains the algorithm identifier for the algorithm used by the CA to sign the certificate.

This field MUST contain the same algorithm identifier as the signatureAlgorithm field in the sequence Certificate (section 4.1.1.2). The contents of the optional parameters field will vary according to the algorithm identified. [PKIXALGS] lists the supported signature algorithms, but other signature algorithms MAY also be supported.

4.1.2.4 Issuer

The issuer field identifies the entity who has signed and issued the certificate. The issuer field MUST contain a non-empty distinguished name (DN). The issuer field is defined as the X.501 type Name [X.501]. Name is defined by the following ASN.1 structures:

Name ::= CHOICE {

RDNSequence }

RDNSequence ::=

SEQUENCE OF RelativeDistinguishedName

RelativeDistinguishedName ::= SET OF AttributeTypeAndValue

AttributeTypeAndValue ::= SEQUENCE {

type AttributeType,
value AttributeValue }

AttributeType ::= OBJECT IDENTIFIER

AttributeValue ::= ANY DEFINED BY AttributeType

DirectoryString ::= CHOICE {

teletexString TeletexString (SIZE (1..MAX)),
printableString PrintableString (SIZE (1..MAX)),
universalString UniversalString (SIZE (1..MAX)),
utf8String UTF8String (SIZE (1..MAX)),
bmpString BMPString (SIZE (1..MAX)) }

The Name describes a hierarchical name composed of attributes, such as country name, and corresponding values, such as US. The type of the component AttributeValue is determined by the AttributeType; in general it will be a DirectoryString.

The DirectoryString type is defined as a choice of PrintableString, TeletexString, BMPString, UTF8String, and UniversalString. The UTF8String encoding [RFC 2279] is the preferred encoding, and all certificates issued after December 31, 2003 MUST use the UTF8String encoding of DirectoryString (except as noted below). Until that date, conforming CAs MUST choose from the following options when creating a distinguished name, including their own:

(a) if the character set is sufficient, the string MAY be represented as a PrintableString;

(b) failing (a), if the BMPString character set is sufficient the string MAY be represented as a BMPString; and

(c) failing (a) and (b), the string MUST be represented as a UTF8String. If (a) or (b) is satisfied, the CA MAY still choose to represent the string as a UTF8String.

Exceptions to the December 31, 2003 UTF8 encoding requirements are as follows:

(a) CAs MAY issue "name rollover" certificates to support an orderly migration to UTF8String encoding. Such certificates would include the CA's UTF8String encoded name as issuer and and the old name encoding as subject, or vice-versa.

(b) As stated in section 4.1.2.6, the subject field MUST be populated with a non-empty distinguished name matching the contents of the issuer field in all certificates issued by the subject CA regardless of encoding.

The TeletexString and UniversalString are included for backward compatibility, and SHOULD NOT be used for certificates for new subjects. However, these types MAY be used in certificates where the name was previously established. Certificate users SHOULD be prepared to receive certificates with these types.

In addition, many legacy implementations support names encoded in the ISO 8859-1 character set (Latin1String) [ISO 8859-1] but tag them as TeletexString. TeletexString encodes a larger character set than ISO 8859-1, but it encodes some characters differently. Implementations SHOULD be prepared to handle both encodings.

As noted above, distinguished names are composed of attributes. This specification does not restrict the set of attribute types that may appear in names. However, conforming implementations MUST be prepared to receive certificates with issuer names containing the set of attribute types defined below. This specification RECOMMENDS support for additional attribute types.

Standard sets of attributes have been defined in the X.500 series of specifications [X.520]. Implementations of this specification MUST be prepared to receive the following standard attribute types in issuer and subject (section 4.1.2.6) names:

* country,
* organization,
* organizational-unit,
* distinguished name qualifier,
* state or province name,
* common name (e.g., "Susan Housley"), and
* serial number.

In addition, implementations of this specification SHOULD be prepared to receive the following standard attribute types in issuer and subject names:

* locality,
* title,
* surname,
* given name,
* initials, * pseudonym, and
* generation qualifier (e.g., "Jr.", "3rd", or "IV").

The syntax and associated object identifiers (OIDs) for these attribute types are provided in the ASN.1 modules in Appendix A.

In addition, implementations of this specification MUST be prepared to receive the domainComponent attribute, as defined in [RFC 2247]. The Domain Name System (DNS) provides a hierarchical resource labeling system. This attribute provides a convenient mechanism for organizations that wish to use DNs that parallel their DNS names. This is not a replacement for the dNSName component of the

alternative name field. Implementations are not required to convert such names into DNS names. The syntax and associated OID for this attribute type is provided in the ASN.1 modules in Appendix A.

Certificate users MUST be prepared to process the issuer distinguished name and subject distinguished name (section 4.1.2.6) fields to perform name chaining for certification path validation (section 6). Name chaining is performed by matching the issuer distinguished name in one certificate with the subject name in a CA certificate.

This specification requires only a subset of the name comparison functionality specified in the X.500 series of specifications. Conforming implementations are REQUIRED to implement the following name comparison rules:

(a) attribute values encoded in different types (e.g., PrintableString and BMPString) MAY be assumed to represent different strings;

(b) attribute values in types other than PrintableString are case sensitive (this permits matching of attribute values as binary objects);

(c) attribute values in PrintableString are not case sensitive (e.g., "Marianne Swanson" is the same as "MARIANNE SWANSON"); and

(d) attribute values in PrintableString are compared after removing leading and trailing white space and converting internal substrings of one or more consecutive white space characters to a single space.

These name comparison rules permit a certificate user to validate certificates issued using languages or encodings unfamiliar to the certificate user.

In addition, implementations of this specification MAY use these comparison rules to process unfamiliar attribute types for name chaining. This allows implementations to process certificates with unfamiliar attributes in the issuer name.

Note that the comparison rules defined in the X.500 series of specifications indicate that the character sets used to encode data in distinguished names are irrelevant. The characters themselves are compared without regard to encoding. Implementations of this profile are permitted to use the comparison algorithm defined in the X.500 series. Such an implementation will recognize a superset of name matches recognized by the algorithm specified above.

4.1.2.5 Validity

The certificate validity period is the time interval during which the CA warrants that it will maintain information about the status of the certificate. The field is represented as a SEQUENCE of two dates: the date on which the certificate validity period begins (notBefore) and the date on which the certificate validity period ends (notAfter). Both notBefore and notAfter may be encoded as UTCTime or GeneralizedTime.

CAs conforming to this profile MUST always encode certificate validity dates through the year 2049 as UTCTime; certificate validity dates in 2050 or later MUST be encoded as GeneralizedTime.

The validity period for a certificate is the period of time from notBefore through notAfter, inclusive.

4.1.2.5.1 UTCTime

The universal time type, UTCTime, is a standard ASN.1 type intended for representation of dates and time. UTCTime specifies the year through the two low order digits and time is specified to the precision of one minute or one second. UTCTime includes either Z (for Zulu, or Greenwich Mean Time) or a time differential.

For the purposes of this profile, UTCTime values MUST be expressed Greenwich Mean Time (Zulu) and MUST include seconds (i.e., times are YYMMDDHHMMSSZ), even where the number of seconds is zero. Conforming systems MUST interpret the year field (YY) as follows:

Where YY is greater than or equal to 50, the year SHALL be interpreted as 19YY; and

Where YY is less than 50, the year SHALL be interpreted as 20YY.

4.1.2.5.2 GeneralizedTime

The generalized time type, GeneralizedTime, is a standard ASN.1 type for variable precision representation of time. Optionally, the GeneralizedTime field can include a representation of the time differential between local and Greenwich Mean Time.

For the purposes of this profile, GeneralizedTime values MUST be expressed Greenwich Mean Time (Zulu) and MUST include seconds (i.e., times are YYYYMMDDHHMMSSZ), even where the number of seconds is zero. GeneralizedTime values MUST NOT include fractional seconds.

4.1.2.6 Subject

The subject field identifies the entity associated with the public key stored in the subject public key field. The subject name MAY be carried in the subject field and/or the subjectAltName extension. If the subject is a CA (e.g., the basic constraints extension, as discussed in 4.2.1.10, is present and the value of cA is TRUE), then the subject field MUST be populated with a non-empty distinguished name matching the contents of the issuer field (section 4.1.2.4) in all certificates issued by the subject CA. If the subject is a CRL issuer (e.g., the key usage extension, as discussed in 4.2.1.3, is present and the value of cRLSign is TRUE) then the subject field MUST be populated with a non-empty distinguished name matching the contents of the issuer field (section 4.1.2.4) in all CRLs issued by the subject CRL issuer. If subject naming information is present only in the subjectAltName extension (e.g., a key bound only to an email address or URI), then the subject name MUST be an empty sequence and the subjectAltName extension MUST be critical.

Where it is non-empty, the subject field MUST contain an X.500 distinguished name (DN). The DN MUST be unique for each subject entity certified by the one CA as defined by the issuer name field. A CA MAY issue more than one certificate with the same DN to the same subject entity.

The subject name field is defined as the X.501 type Name. Implementation requirements for this field are those defined for the issuer field (section 4.1.2.4). When encoding attribute values of type DirectoryString, the encoding rules for the issuer field MUST be implemented. Implementations of this specification MUST be prepared to receive subject names containing the attribute types required for the issuer field. Implementations of this specification SHOULD be prepared to receive subject names containing the recommended attribute types for the issuer field. The syntax and associated object identifiers (OIDs) for these attribute types are provided in the ASN.1 modules in Appendix A. Implementations of this specification MAY use these comparison rules to process unfamiliar attribute types (i.e., for name chaining). This allows implementations to process certificates with unfamiliar attributes in the subject name.

In addition, legacy implementations exist where an RFC 822 name is embedded in the subject distinguished name as an EmailAddress attribute. The attribute value for EmailAddress is of type IA5String to permit inclusion of the character '@', which is not part of the PrintableString character set. EmailAddress attribute values are not case sensitive (e.g., "fanfeedback@redsox.com" is the same as "FANFEEDBACK@REDSOX.COM").

Conforming implementations generating new certificates with electronic mail addresses MUST use the rfc822Name in the subject alternative name field (section 4.2.1.7) to describe such identities. Simultaneous inclusion of the EmailAddress attribute in the subject distinguished name to support legacy implementations is deprecated but permitted.

4.1.2.7 Subject Public Key Info

This field is used to carry the public key and identify the algorithm with which the key is used (e.g., RSA, DSA, or Diffie-Hellman). The algorithm is identified using the AlgorithmIdentifier structure specified in section 4.1.1.2. The object identifiers for the supported algorithms and the methods for encoding the public key materials (public key and parameters) are specified in [PKIXALGS].

4.1.2.8 Unique Identifiers

These fields MUST only appear if the version is 2 or 3 (section 4.1.2.1). These fields MUST NOT appear if the version is 1. The subject and issuer unique identifiers are present in the certificate to handle the possibility of reuse of subject and/or issuer names over time. This profile RECOMMENDS that names not be reused for different entities and that Internet certificates not make use of unique identifiers. CAs conforming to this profile SHOULD NOT generate certificates with unique identifiers. Applications conforming to this profile SHOULD be capable of parsing unique identifiers.

4.1.2.9 Extensions

This field MUST only appear if the version is 3 (section 4.1.2.1). If present, this field is a SEQUENCE of one or more certificate extensions. The format and content of certificate extensions in the Internet PKI is defined in section 4.2.

4.2 Certificate Extensions

The extensions defined for X.509 v3 certificates provide methods for associating additional attributes with users or public keys and for managing a certification hierarchy. The X.509 v3 certificate format also allows communities to define private extensions to carry information unique to those communities. Each extension in a certificate is designated as either critical or non-critical. A certificate using system MUST reject the certificate if it encounters a critical extension it does not recognize; however, a non-critical extension MAY be ignored if it is not recognized. The following sections present recommended extensions used within Internet certificates and standard locations for information. Communities may elect to use additional extensions; however, caution ought to be exercised in adopting any critical extensions in certificates which might prevent use in a general context.

Each extension includes an OID and an ASN.1 structure. When an extension appears in a certificate, the OID appears as the field extnID and the corresponding ASN.1 encoded structure is the value of the octet string extnValue. A certificate MUST NOT include more than one instance of a particular extension. For example, a certificate may contain only one authority key identifier extension (section 4.2.1.1). An extension includes the boolean critical, with a default value of FALSE. The text for each extension specifies the acceptable values for the critical field.

Conforming CAs MUST support key identifiers (sections 4.2.1.1 and 4.2.1.2), basic constraints (section 4.2.1.10), key usage (section 4.2.1.3), and certificate policies (section 4.2.1.5) extensions. If the CA issues certificates with an empty sequence for the subject field, the CA MUST support the subject alternative name extension (section 4.2.1.7). Support for the remaining extensions is OPTIONAL. Conforming CAs MAY support extensions that are not identified within this specification; certificate issuers are cautioned that marking such extensions as critical may inhibit interoperability.

At a minimum, applications conforming to this profile MUST recognize the following extensions: key usage (section 4.2.1.3), certificate policies (section 4.2.1.5), the subject alternative name (section 4.2.1.7), basic constraints (section 4.2.1.10), name constraints (section 4.2.1.11), policy constraints (section 4.2.1.12), extended key usage (section 4.2.1.13), and inhibit any-policy (section 4.2.1.15).

In addition, applications conforming to this profile SHOULD recognize the authority and subject key identifier (sections 4.2.1.1 and 4.2.1.2), and policy mapping (section 4.2.1.6) extensions.

4.2.1 Standard Extensions

This section identifies standard certificate extensions defined in [X.509] for use in the Internet PKI. Each extension is associated with an OID defined in [X.509]. These OIDs are members of the id-ce arc, which is defined by the following:

id-ce OBJECT IDENTIFIER ::= { joint-iso-ccitt(2) ds(5) 29 }

4.2.1.1 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 certificate. This extension is used where an issuer has multiple signing keys (either due to multiple concurrent key pairs or due to changeover). The identification MAY be based on either the key identifier (the subject key identifier in the issuer's certificate) or on the issuer name and serial number.

The keyIdentifier field of the authorityKeyIdentifier extension MUST be included in all certificates generated by conforming CAs to facilitate certification path construction. There is one exception; where a CA distributes its public key in the form of a "self-signed" certificate, the authority key identifier MAY be omitted. The signature on a self-signed certificate is generated with the private key associated with the certificate's subject public key. (This proves that the issuer possesses both the public and private keys.) In this case, the subject and authority key identifiers would be identical, but only the subject key identifier is needed for certification path building.

The value of the keyIdentifier field SHOULD be derived from the public key used to verify the certificate's signature or a method that generates unique values. Two common methods for generating key identifiers from the public key, and one common method for generating unique values, are described in section 4.2.1.2. Where a key identifier has not been previously established, this specification RECOMMENDS use of one of these methods for generating keyIdentifiers. Where a key identifier has been previously established, the CA SHOULD use the previously established identifier.

This profile RECOMMENDS support for the key identifier method by all certificate users.

This extension MUST NOT be marked critical.

id-ce-authorityKeyIdentifier OBJECT IDENTIFIER ::= { id-ce 35 }

AuthorityKeyIdentifier ::= SEQUENCE { keyIdentifier [0] KeyIdentifier OPTIONAL, authorityCertIssuer [1] GeneralNames OPTIONAL, authorityCertSerialNumber [2] CertificateSerialNumber OPTIONAL }

KeyIdentifier ::= OCTET STRING

4.2.1.2 Subject Key Identifier

The subject key identifier extension provides a means of identifying certificates that contain a particular public key.

To facilitate certification path construction, this extension MUST appear in all conforming CA certificates, that is, all certificates including the basic constraints extension (section 4.2.1.10) where the value of cA is TRUE. The value of the subject key identifier MUST be the value placed in the key identifier field of the Authority Key Identifier extension (section 4.2.1.1) of certificates issued by the subject of this certificate.

For CA certificates, subject key identifiers SHOULD be derived from the public key or a method that generates unique values. Two common methods for generating key identifiers from the public key are:

(1) The keyIdentifier is composed of the 160-bit SHA-1 hash of the value of the BIT STRING subjectPublicKey (excluding the tag, length, and number of unused bits).

(2) The keyIdentifier is composed of a four bit type field with the value 0100 followed by the least significant 60 bits of the SHA-1 hash of the value of the BIT STRING subjectPublicKey (excluding the tag, length, and number of unused bit string bits).

One common method for generating unique values is a monotonically increasing sequence of integers.

For end entity certificates, the subject key identifier extension provides a means for identifying certificates containing the particular public key used in an application. Where an end entity has obtained multiple certificates, especially from multiple CAs, the subject key identifier provides a means to quickly identify the set of certificates containing a particular public key. To assist applications in identifying the appropriate end entity certificate, this extension SHOULD be included in all end entity certificates.

For end entity certificates, subject key identifiers SHOULD be derived from the public key. Two common methods for generating key identifiers from the public key are identified above.

Where a key identifier has not been previously established, this specification RECOMMENDS use of one of these methods for generating keyIdentifiers. Where a key identifier has been previously established, the CA SHOULD use the previously established identifier.

This extension MUST NOT be marked critical.

id-ce-subjectKeyIdentifier OBJECT IDENTIFIER ::= { id-ce 14 }

SubjectKeyIdentifier ::= KeyIdentifier

4.2.1.3 Key Usage

The key usage extension defines the purpose (e.g., encipherment, signature, certificate signing) of the key contained in the certificate. The usage restriction might be employed when a key that could be used for more than one operation is to be restricted. For example, when an RSA key should be used only to verify signatures on objects other than public key certificates and CRLs, the digitalSignature and/or nonRepudiation bits would be asserted. Likewise, when an RSA key should be used only for key management, the keyEncipherment bit would be asserted.

This extension MUST appear in certificates that contain public keys that are used to validate digital signatures on other public key certificates or CRLs. When this extension appears, it SHOULD be marked critical.

id-ce-keyUsage OBJECT IDENTIFIER ::= { id-ce 15 }

KeyUsage ::= BIT STRING { digitalSignature (0), nonRepudiation (1), keyEncipherment (2), dataEncipherment (3), keyAgreement (4), keyCertSign (5), cRLSign (6), encipherOnly (7), decipherOnly (8) }

Bits in the KeyUsage type are used as follows:

The digitalSignature bit is asserted when the subject public key is used with a digital signature mechanism to support security services other than certificate signing (bit 5), or CRL signing (bit 6). Digital signature mechanisms are often used for entity authentication and data origin authentication with integrity.

The nonRepudiation bit is asserted when the subject public key is used to verify digital signatures used to provide a non- repudiation service which protects against the signing entity falsely denying some action, excluding certificate or CRL signing. In the case of later conflict, a reliable third party may determine the authenticity of the signed data.

Further distinctions between the digitalSignature and nonRepudiation bits may be provided in specific certificate policies.

The keyEncipherment bit is asserted when the subject public key is used for key transport. For example, when an RSA key is to be used for key management, then this bit is set.

The dataEncipherment bit is asserted when the subject public key is used for enciphering user data, other than cryptographic keys.

The keyAgreement bit is asserted when the subject public key is used for key agreement. For example, when a Diffie-Hellman key is to be used for key management, then this bit is set.

The keyCertSign bit is asserted when the subject public key is used for verifying a signature on public key certificates. If the keyCertSign bit is asserted, then the cA bit in the basic constraints extension (section 4.2.1.10) MUST also be asserted.

The cRLSign bit is asserted when the subject public key is used for verifying a signature on certificate revocation list (e.g., a CRL, delta CRL, or an ARL). This bit MUST be asserted in certificates that are used to verify signatures on CRLs.

The meaning of the encipherOnly bit is undefined in the absence of the keyAgreement bit. When the encipherOnly bit is asserted and the keyAgreement bit is also set, the subject public key may be used only for enciphering data while performing key agreement.

The meaning of the decipherOnly bit is undefined in the absence of the keyAgreement bit. When the decipherOnly bit is asserted and the keyAgreement bit is also set, the subject public key may be used only for deciphering data while performing key agreement.

This profile does not restrict the combinations of bits that may be set in an instantiation of the keyUsage extension. However, appropriate values for keyUsage extensions for particular algorithms are specified in [PKIXALGS].

4.2.1.4 Private Key Usage Period

This extension SHOULD NOT be used within the Internet PKI. CAs conforming to this profile MUST NOT generate certificates that include a critical private key usage period extension.

The private key usage period extension allows the certificate issuer to specify a different validity period for the private key than the certificate. This extension is intended for use with digital signature keys. This extension consists of two optional components, notBefore and notAfter. The private key associated with the certificate SHOULD NOT be used to sign objects before or after the times specified by the two components, respectively. CAs conforming to this profile MUST NOT generate certificates with private key usage period extensions unless at least one of the two components is present and the extension is non-critical.

Where used, notBefore and notAfter are represented as GeneralizedTime and MUST be specified and interpreted as defined in section 4.1.2.5.2.

id-ce-privateKeyUsagePeriod OBJECT IDENTIFIER ::= { id-ce 16 }

PrivateKeyUsagePeriod ::= SEQUENCE {

notBefore [0] GeneralizedTime OPTIONAL,
notAfter [1] GeneralizedTime OPTIONAL }

4.2.1.5 Certificate Policies

The certificate policies extension contains a sequence of one or more policy information terms, each of which consists of an object identifier (OID) and optional qualifiers. Optional qualifiers, which MAY be present, are not expected to change the definition of the policy.

In an end entity certificate, these policy information terms indicate the policy under which the certificate has been issued and the purposes for which the certificate may be used. In a CA certificate, these policy information terms limit the set of policies for certification paths which include this certificate. When a CA does not wish to limit the set of policies for certification paths which include this certificate, it MAY assert the special policy anyPolicy, with a value of { 2 5 29 32 0 }.

Applications with specific policy requirements are expected to have a list of those policies which they will accept and to compare the policy OIDs in the certificate to that list. If this extension is critical, the path validation software MUST be able to interpret this extension (including the optional qualifier), or MUST reject the certificate.

To promote interoperability, this profile RECOMMENDS that policy information terms consist of only an OID. Where an OID alone is insufficient, this profile strongly recommends that use of qualifiers be limited to those identified in this section. When qualifiers are used with the special policy anyPolicy, they MUST be limited to the qualifiers identified in this section.

This specification defines two policy qualifier types for use by certificate policy writers and certificate issuers. The qualifier types are the CPS Pointer and User Notice qualifiers.

The CPS Pointer qualifier contains a pointer to a Certification Practice Statement (CPS) published by the CA. The pointer is in the form of a URI. Processing requirements for this qualifier are a local matter. No action is mandated by this specification regardless of the criticality value asserted for the extension.

User notice is intended for display to a relying party when a certificate is used. The application software SHOULD display all user notices in all certificates of the certification path used, except that if a notice is duplicated only one copy need be displayed. To prevent such duplication, this qualifier SHOULD only be present in end entity certificates and CA certificates issued to other organizations.

The user notice has two optional fields: the noticeRef field and the explicitText field.

The noticeRef field, if used, names an organization and identifies, by number, a particular textual statement prepared by that organization. For example, it might identify the organization "CertsRUs" and notice number 1. In a typical implementation, the application software will have a notice file containing the current set of notices for CertsRUs; the application will extract the notice text from the file and display it. Messages MAY be multilingual, allowing the software to select the particular language message for its own environment.

An explicitText field includes the textual statement directly in the certificate. The explicitText field is a string with a maximum size of 200 characters.

If both the noticeRef and explicitText options are included in the one qualifier and if the application software can locate the notice text indicated by the noticeRef option, then that text SHOULD be displayed; otherwise, the explicitText string SHOULD be displayed.

Note: While the explicitText has a maximum size of 200 characters, some non-conforming CAs exceed this limit. Therefore, certificate users SHOULD gracefully handle explicitText with more than 200 characters.

id-ce-certificatePolicies OBJECT IDENTIFIER ::= { id-ce 32 }

anyPolicy OBJECT IDENTIFIER ::= { id-ce-certificate-policies 0 }

certificatePolicies ::= SEQUENCE SIZE (1..MAX) OF PolicyInformation

PolicyInformation ::= SEQUENCE {

policyIdentifier CertPolicyId,
policyQualifiers SEQUENCE SIZE (1..MAX) OF PolicyQualifierInfo OPTIONAL }

CertPolicyId ::= OBJECT IDENTIFIER

PolicyQualifierInfo ::= SEQUENCE {

policyQualifierId PolicyQualifierId,
qualifier ANY DEFINED BY policyQualifierId }

-- policyQualifierIds for Internet policy qualifiers

id-qt OBJECT IDENTIFIER ::= { id-pkix 2 }
id-qt-cps OBJECT IDENTIFIER ::= { id-qt 1 }
id-qt-unotice OBJECT IDENTIFIER ::= { id-qt 2 }

PolicyQualifierId ::= OBJECT IDENTIFIER ( id-qt-cps | id-qt-unotice )

Qualifier ::= CHOICE {

cPSuri CPSuri,
userNotice UserNotice }

CPSuri ::= IA5String

UserNotice ::= SEQUENCE {

noticeRef NoticeReference OPTIONAL,
explicitText DisplayText OPTIONAL}

NoticeReference ::= SEQUENCE { organization DisplayText, noticeNumbers SEQUENCE OF INTEGER }

DisplayText ::= CHOICE {

ia5String IA5String (SIZE (1..200)),
visibleString VisibleString (SIZE (1..200)),
bmpString BMPString (SIZE (1..200)),
utf8String UTF8String (SIZE (1..200)) }

4.2.1.6 Policy Mappings

This extension is used in CA certificates. It lists one or more pairs of OIDs; each pair includes an issuerDomainPolicy and a subjectDomainPolicy. The pairing indicates the issuing CA considers its issuerDomainPolicy equivalent to the subject CA's subjectDomainPolicy.

The issuing CA's users might accept an issuerDomainPolicy for certain applications. The policy mapping defines the list of policies associated with the subject CA that may be accepted as comparable to the issuerDomainPolicy.

Each issuerDomainPolicy named in the policy mapping extension SHOULD also be asserted in a certificate policies extension in the same certificate. Policies SHOULD NOT be mapped either to or from the special value anyPolicy (section 4.2.1.5).

This extension MAY be supported by CAs and/or applications, and it MUST be non-critical.

id-ce-policyMappings OBJECT IDENTIFIER ::= { id-ce 33 }

PolicyMappings ::= SEQUENCE SIZE (1..MAX) OF SEQUENCE {

issuerDomainPolicy CertPolicyId,
subjectDomainPolicy CertPolicyId }

4.2.1.7 Subject Alternative Name

The subject alternative names extension allows additional identities to be bound to the subject of the certificate. Defined options include an Internet electronic mail address, a DNS name, an IP address, and a uniform resource identifier (URI). Other options exist, including completely local definitions. Multiple name forms, and multiple instances of each name form, MAY be included. Whenever such identities are to be bound into a certificate, the subject alternative name (or issuer alternative name) extension MUST be used; however, a DNS name MAY be represented in the subject field using the domainComponent attribute as described in section 4.1.2.4.

Because the subject alternative name is considered to be definitively bound to the public key, all parts of the subject alternative name MUST be verified by the CA.

Further, if the only subject identity included in the certificate is an alternative name form (e.g., an electronic mail address), then the subject distinguished name MUST be empty (an empty sequence), and the subjectAltName extension MUST be present. If the subject field contains an empty sequence, the subjectAltName extension MUST be marked critical.

When the subjectAltName extension contains an Internet mail address, the address MUST be included as an rfc822Name. The format of an rfc822Name is an "addr-spec" as defined in RFC 822 [RFC 822]. An addr-spec has the form "local-part@domain". Note that an addr-spec has no phrase (such as a common name) before it, has no comment (text surrounded in parentheses) after it, and is not surrounded by "<" and ">". Note that while upper and lower case letters are allowed in an RFC 822 addr-spec, no significance is attached to the case.

When the subjectAltName extension contains a iPAddress, the address MUST be stored in the octet string in "network byte order," as specified in RFC 791 [RFC 791]. The least significant bit (LSB) of each octet is the LSB of the corresponding byte in the network address. For IP Version 4, as specified in RFC 791, the octet string MUST contain exactly four octets. For IP Version 6, as specified in RFC 1883, the octet string MUST contain exactly sixteen octets [RFC 1883].

When the subjectAltName extension contains a domain name system label, the domain name MUST be stored in the dNSName (an IA5String). The name MUST be in the "preferred name syntax," as specified by RFC 1034 [RFC 1034]. Note that while upper and lower case letters are allowed in domain names, no signifigance is attached to the case. In addition, while the string " " is a legal domain name, subjectAltName extensions with a dNSName of " " MUST NOT be used. Finally, the use of the DNS representation for Internet mail addresses (wpolk.nist.gov instead of wpolk@nist.gov) MUST NOT be used; such identities are to be encoded as rfc822Name.

Note: work is currently underway to specify domain names in international character sets. Such names will likely not be accommodated by IA5String. Once this work is complete, this profile will be revisited and the appropriate functionality will be added.

When the subjectAltName extension contains a URI, the name MUST be stored in the uniformResourceIdentifier (an IA5String). The name MUST NOT be a relative URL, and it MUST follow the URL syntax and encoding rules specified in [RFC 1738]. The name MUST include both a scheme (e.g., "http" or "ftp") and a scheme-specific-part. The scheme-specific-part MUST include a fully qualified domain name or IP address as the host.

As specified in [RFC 1738], the scheme name is not case-sensitive (e.g., "http" is equivalent to "HTTP"). The host part is also not case-sensitive, but other components of the scheme-specific-part may be case-sensitive. When comparing URIs, conforming implementations MUST compare the scheme and host without regard to case, but assume the remainder of the scheme-specific-part is case sensitive.

When the subjectAltName extension contains a DN in the directoryName, the DN MUST be unique for each subject entity certified by the one CA as defined by the issuer name field. A CA MAY issue more than one certificate with the same DN to the same subject entity.

The subjectAltName MAY carry additional name types through the use of the otherName field. The format and semantics of the name are indicated through the OBJECT IDENTIFIER in the type-id field. The name itself is conveyed as value field in otherName. For example, Kerberos [RFC 1510] format names can be encoded into the otherName, using using a Kerberos 5 principal name OID and a SEQUENCE of the Realm and the PrincipalName.

Subject alternative names MAY be constrained in the same manner as subject distinguished names using the name constraints extension as described in section 4.2.1.11.

If the subjectAltName extension is present, the sequence MUST contain at least one entry. Unlike the subject field, conforming CAs MUST NOT issue certificates with subjectAltNames containing empty GeneralName fields. For example, an rfc822Name is represented as an IA5String. While an empty string is a valid IA5String, such an rfc822Name is not permitted by this profile. The behavior of clients that encounter such a certificate when processing a certificication path is not defined by this profile.

Finally, the semantics of subject alternative names that include wildcard characters (e.g., as a placeholder for a set of names) are not addressed by this specification. Applications with specific requirements MAY use such names, but they must define the semantics.

id-ce-subjectAltName OBJECT IDENTIFIER ::= { id-ce 17 }

SubjectAltName ::= GeneralNames

GeneralNames ::= SEQUENCE SIZE (1..MAX) OF GeneralName

GeneralName ::= CHOICE {

otherName [0] OtherName,
rfc822Name [1] IA5String,
dNSName [2] IA5String,
x400Address [3] ORAddress,
directoryName [4] Name,
ediPartyName [5] EDIPartyName,
uniformResourceIdentifier [6] IA5String,
iPAddress [7] OCTET STRING,
registeredID [8] OBJECT IDENTIFIER }

OtherName ::= SEQUENCE {

type-id OBJECT IDENTIFIER,
value [0] EXPLICIT ANY DEFINED BY type-id }

EDIPartyName ::= SEQUENCE {

nameAssigner [0] DirectoryString OPTIONAL,
partyName [1] DirectoryString }

4.2.1.8 Issuer Alternative Names

As with 4.2.1.7, this extension is used to associate Internet style identities with the certificate issuer. Issuer alternative names MUST be encoded as in 4.2.1.7.

Where present, this extension SHOULD NOT be marked critical.

id-ce-issuerAltName OBJECT IDENTIFIER ::= { id-ce 18 }

IssuerAltName ::= GeneralNames

4.2.1.9 Subject Directory Attributes

The subject directory attributes extension is used to convey identification attributes (e.g., nationality) of the subject. The extension is defined as a sequence of one or more attributes. This extension MUST be non-critical.

id-ce-subjectDirectoryAttributes OBJECT IDENTIFIER ::= { id-ce 9 }

SubjectDirectoryAttributes ::= SEQUENCE SIZE (1..MAX) OF Attribute

4.2.1.10 Basic Constraints

The basic constraints extension identifies whether the subject of the certificate is a CA and the maximum depth of valid certification paths that include this certificate.

The cA boolean indicates whether the certified public key belongs to a CA. If the cA boolean is not asserted, then the keyCertSign bit in the key usage extension MUST NOT be asserted.

The pathLenConstraint field is meaningful only if the cA boolean is asserted and the key usage extension asserts the keyCertSign bit (section 4.2.1.3). In this case, it gives the maximum number of non- self-issued intermediate certificates that may follow this certificate in a valid certification path. A certificate is self- issued if the DNs that appear in the subject and issuer fields are identical and are not empty. (Note: The last certificate in the certification path is not an intermediate certificate, and is not included in this limit. Usually, the last certificate is an end entity certificate, but it can be a CA certificate.) A pathLenConstraint of zero indicates that only one more certificate may follow in a valid certification path. Where it appears, the pathLenConstraint field MUST be greater than or equal to zero. Where pathLenConstraint does not appear, no limit is imposed.

This extension MUST appear as a critical extension in all CA certificates that contain public keys used to validate digital signatures on certificates. This extension MAY appear as a critical or non-critical extension in CA certificates that contain public keys used exclusively for purposes other than validating digital signatures on certificates. Such CA certificates include ones that contain public keys used exclusively for validating digital signatures on CRLs and ones that contain key management public keys used with certificate enrollment protocols. This extension MAY appear as a critical or non-critical extension in end entity certificates.

CAs MUST NOT include the pathLenConstraint field unless the cA boolean is asserted and the key usage extension asserts the keyCertSign bit.

id-ce-basicConstraints OBJECT IDENTIFIER ::= { id-ce 19 }

BasicConstraints ::= SEQUENCE {

cA BOOLEAN DEFAULT FALSE,
pathLenConstraint INTEGER (0..MAX) OPTIONAL }

4.2.1.11 Name Constraints

The name constraints extension, which MUST be used only in a CA certificate, indicates a name space within which all subject names in subsequent certificates in a certification path MUST be located. Restrictions apply to the subject distinguished name and apply to subject alternative names. Restrictions apply only when the specified name form is present. If no name of the type is in the certificate, the certificate is acceptable.

Name constraints are not applied to certificates whose issuer and subject are identical (unless the certificate is the final certificate in the path). (This could prevent CAs that use name constraints from employing self-issued certificates to implement key rollover.)

Restrictions are defined in terms of permitted or excluded name subtrees. Any name matching a restriction in the excludedSubtrees field is invalid regardless of information appearing in the permittedSubtrees. This extension MUST be critical.

Within this profile, the minimum and maximum fields are not used with any name forms, thus minimum MUST be zero, and maximum MUST be absent.

For URIs, the constraint applies to the host part of the name. The constraint MAY specify a host or a domain. Examples would be "foo.bar.com"; and ".xyz.com". When the the constraint begins with a period, it MAY be expanded with one or more subdomains. That is, the constraint ".xyz.com" is satisfied by both abc.xyz.com and abc.def.xyz.com. However, the constraint ".xyz.com" is not satisfied by "xyz.com". When the constraint does not begin with a period, it specifies a host.

A name constraint for Internet mail addresses MAY specify a particular mailbox, all addresses at a particular host, or all mailboxes in a domain. To indicate a particular mailbox, the constraint is the complete mail address. For example, "root@xyz.com" indicates the root mailbox on the host "xyz.com". To indicate all Internet mail addresses on a particular host, the constraint is specified as the host name. For example, the constraint "xyz.com" is satisfied by any mail address at the host "xyz.com". To specify any address within a domain, the constraint is specified with a leading period (as with URIs). For example, ".xyz.com" indicates all the Internet mail addresses in the domain "xyz.com", but not Internet mail addresses on the host "xyz.com".

DNS name restrictions are expressed as foo.bar.com. Any DNS name that can be constructed by simply adding to the left hand side of the name satisfies the name constraint. For example, www.foo.bar.com would satisfy the constraint but foo1.bar.com would not.

Legacy implementations exist where an RFC 822 name is embedded in the subject distinguished name in an attribute of type EmailAddress (section 4.1.2.6). When rfc822 names are constrained, but the certificate does not include a subject alternative name, the rfc822 name constraint MUST be applied to the attribute of type EmailAddress in the subject distinguished name. The ASN.1 syntax for EmailAddress and the corresponding OID are supplied in Appendix A.

Restrictions of the form directoryName MUST be applied to the subject field in the certificate and to the subjectAltName extensions of type directoryName. Restrictions of the form x400Address MUST be applied to subjectAltName extensions of type x400Address.

When applying restrictions of the form directoryName, an implementation MUST compare DN attributes. At a minimum, implementations MUST perform the DN comparison rules specified in Section 4.1.2.4. CAs issuing certificates with a restriction of the form directoryName SHOULD NOT rely on implementation of the full ISO DN name comparison algorithm. This implies name restrictions MUST be stated identically to the encoding used in the subject field or subjectAltName extension.

The syntax of iPAddress MUST be as described in section 4.2.1.7 with the following additions specifically for Name Constraints. For IPv4 addresses, the ipAddress field of generalName MUST contain eight (8) octets, encoded in the style of RFC 1519 (CIDR) to represent an address range [RFC 1519]. For IPv6 addresses, the ipAddress field MUST contain 32 octets similarly encoded. For example, a name constraint for "class C" subnet 10.9.8.0 is represented as the octets 0A 09 08 00 FF FF FF 00, representing the CIDR notation 10.9.8.0/255.255.255.0.

The syntax and semantics for name constraints for otherName, ediPartyName, and registeredID are not defined by this specification.

id-ce-nameConstraints OBJECT IDENTIFIER ::= { id-ce 30 }

NameConstraints ::= SEQUENCE {

permittedSubtrees [0] GeneralSubtrees OPTIONAL,
excludedSubtrees [1] GeneralSubtrees OPTIONAL }

GeneralSubtrees ::= SEQUENCE SIZE (1..MAX) OF GeneralSubtree

GeneralSubtree ::= SEQUENCE {

base GeneralName,
minimum [0] BaseDistance DEFAULT 0,
maximum [1] BaseDistance OPTIONAL }

BaseDistance ::= INTEGER (0..MAX)

4.2.1.12 Policy Constraints

The policy constraints extension can be used in certificates issued to CAs. The policy constraints extension constrains path validation in two ways. It can be used to prohibit policy mapping or require that each certificate in a path contain an acceptable policy identifier.

If the inhibitPolicyMapping field is present, the value indicates the number of additional certificates that may appear in the path before policy mapping is no longer permitted. For example, a value of one indicates that policy mapping may be processed in certificates issued by the subject of this certificate, but not in additional certificates in the path.

If the requireExplicitPolicy field is present, the value of requireExplicitPolicy indicates the number of additional certificates that may appear in the path before an explicit policy is required for the entire path. When an explicit policy is required, it is necessary for all certificates in the path to contain an acceptable policy identifier in the certificate policies extension. An acceptable policy identifier is the identifier of a policy required by the user of the certification path or the identifier of a policy which has been declared equivalent through policy mapping.

Conforming CAs MUST NOT issue certificates where policy constraints is a empty sequence. That is, at least one of the inhibitPolicyMapping field or the requireExplicitPolicy field MUST be present. The behavior of clients that encounter a empty policy constraints field is not addressed in this profile.

This extension MAY be critical or non-critical.

id-ce-policyConstraints OBJECT IDENTIFIER ::= { id-ce 36 }

PolicyConstraints ::= SEQUENCE {

requireExplicitPolicy [0] SkipCerts OPTIONAL,
inhibitPolicyMapping [1] SkipCerts OPTIONAL }

SkipCerts ::= INTEGER (0..MAX)

4.2.1.13 Extended Key Usage

This extension indicates one or more purposes for which the certified public key may be used, in addition to or in place of the basic purposes indicated in the key usage extension. In general, this extension will appear only in end entity certificates. This extension is defined as follows:

id-ce-extKeyUsage OBJECT IDENTIFIER ::= { id-ce 37 }

ExtKeyUsageSyntax ::= SEQUENCE SIZE (1..MAX) OF KeyPurposeId

KeyPurposeId ::= OBJECT IDENTIFIER

Key purposes may be defined by any organization with a need. Object identifiers used to identify key purposes MUST be assigned in accordance with IANA or ITU-T Recommendation X.660 [X.660].

This extension MAY, at the option of the certificate issuer, be either critical or non-critical.

If the extension is present, then the certificate MUST only be used for one of the purposes indicated. If multiple purposes are indicated the application need not recognize all purposes indicated, as long as the intended purpose is present. Certificate using applications MAY require that a particular purpose be indicated in order for the certificate to be acceptable to that application.

If a CA includes extended key usages to satisfy such applications, but does not wish to restrict usages of the key, the CA can include the special keyPurposeID anyExtendedKeyUsage. If the anyExtendedKeyUsage keyPurposeID is present, the extension SHOULD NOT be critical.

If a certificate contains both a key usage extension and an extended key usage extension, then both extensions MUST be processed independently and the certificate MUST only be used for a purpose consistent with both extensions. If there is no purpose consistent with both extensions, then the certificate MUST NOT be used for any purpose.

The following key usage purposes are defined:

anyExtendedKeyUsage OBJECT IDENTIFIER ::= { id-ce-extKeyUsage 0 }

id-kp OBJECT IDENTIFIER ::= { id-pkix 3 }

id-kp-serverAuth OBJECT IDENTIFIER ::= { id-kp 1 }
-- TLS WWW server authentication
-- Key usage bits that may be consistent: digitalSignature,
-- keyEncipherment or keyAgreement

id-kp-clientAuth OBJECT IDENTIFIER ::= { id-kp 2 }
-- TLS WWW client authentication
-- Key usage bits that may be consistent: digitalSignature
-- and/or keyAgreement

id-kp-codeSigning OBJECT IDENTIFIER ::= { id-kp 3 }
-- Signing of downloadable executable code
-- Key usage bits that may be consistent: digitalSignature

id-kp-emailProtection OBJECT IDENTIFIER ::= { id-kp 4 }
-- E-mail protection
-- Key usage bits that may be consistent: digitalSignature,
-- nonRepudiation, and/or (keyEncipherment or keyAgreement)

id-kp-timeStamping OBJECT IDENTIFIER ::= { id-kp 8 }
-- Binding the hash of an object to a time
-- Key usage bits that may be consistent: digitalSignature
-- and/or nonRepudiation

id-kp-OCSPSigning OBJECT IDENTIFIER ::= { id-kp 9 }
-- Signing OCSP responses
-- Key usage bits that may be consistent: digitalSignature
-- and/or nonRepudiation

4.2.1.14 CRL Distribution Points

The CRL distribution points extension identifies how CRL information is obtained. The extension SHOULD be non-critical, but this profile RECOMMENDS support for this extension by CAs and applications. Further discussion of CRL management is contained in section 5.

The cRLDistributionPoints extension is a SEQUENCE of DistributionPoint. A DistributionPoint consists of three fields, each of which is optional: distributionPoint, reasons, and cRLIssuer. While each of these fields is optional, a DistributionPoint MUST NOT consist of only the reasons field; either distributionPoint or cRLIssuer MUST be present. If the certificate issuer is not the CRL issuer, then the cRLIssuer field MUST be present and contain the Name of the CRL issuer. If the certificate issuer is also the CRL issuer, then the cRLIssuer field MUST be omitted and the distributionPoint field MUST be present. If the distributionPoint field is omitted, cRLIssuer MUST be present and include a Name corresponding to an X.500 or LDAP directory entry where the CRL is located.

When the distributionPoint field is present, it contains either a SEQUENCE of general names or a single value, nameRelativeToCRLIssuer. If the cRLDistributionPoints extension contains a general name of type URI, the following semantics MUST be assumed: the URI is a pointer to the current CRL for the associated reasons and will be issued by the associated cRLIssuer. The expected values for the URI are those defined in 4.2.1.7. Processing rules for other values are not defined by this specification.

If the DistributionPointName contains multiple values, each name describes a different mechanism to obtain the same CRL. For example, the same CRL could be available for retrieval through both LDAP and HTTP.

If the DistributionPointName contains the single value nameRelativeToCRLIssuer, the value provides a distinguished name fragment. The fragment is appended to the X.500 distinguished name of the CRL issuer to obtain the distribution point name. If the cRLIssuer field in the DistributionPoint is present, then the name fragment is appended to the distinguished name that it contains; otherwise, the name fragment is appended to the certificate issuer distinguished name. The DistributionPointName MUST NOT use the nameRealtiveToCRLIssuer alternative when cRLIssuer contains more than one distinguished name.

If the DistributionPoint omits the reasons field, the CRL MUST include revocation information for all reasons.

The cRLIssuer identifies the entity who signs and issues the CRL. If present, the cRLIssuer MUST contain at least one an X.500 distinguished name (DN), and MAY also contain other name forms. Since the cRLIssuer is compared to the CRL issuer name, the X.501 type Name MUST follow the encoding rules for the issuer name field in the certificate (section 4.1.2.4).

id-ce-cRLDistributionPoints OBJECT IDENTIFIER ::= { id-ce 31 }

CRLDistributionPoints ::= SEQUENCE SIZE (1..MAX) OF DistributionPoint

DistributionPoint ::= SEQUENCE {

distributionPoint [0] DistributionPointName OPTIONAL,
reasons [1] ReasonFlags OPTIONAL,
cRLIssuer [2] GeneralNames OPTIONAL }

DistributionPointName ::= CHOICE {

fullName [0] GeneralNames,
nameRelativeToCRLIssuer [1] RelativeDistinguishedName }

ReasonFlags ::= BIT STRING {

unused (0),
keyCompromise (1),
cACompromise (2),
affiliationChanged (3),
superseded (4),
cessationOfOperation (5),
certificateHold (6),
privilegeWithdrawn (7),
aACompromise (8) }

4.2.1.15 Inhibit Any-Policy

The inhibit any-policy extension can be used in certificates issued to CAs. The inhibit any-policy indicates that the special anyPolicy OID, with the value { 2 5 29 32 0 }, is not considered an explicit match for other certificate policies. The value indicates the number of additional certificates that may appear in the path before anyPolicy is no longer permitted. For example, a value of one indicates that anyPolicy may be processed in certificates issued by the subject of this certificate, but not in additional certificates in the path.

This extension MUST be critical.

id-ce-inhibitAnyPolicy OBJECT IDENTIFIER ::= { id-ce 54 }

InhibitAnyPolicy ::= SkipCerts

SkipCerts ::= INTEGER (0..MAX)

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

The freshest CRL extension identifies how delta CRL information is obtained. The extension MUST be non-critical. Further discussion of CRL management is contained in section 5.

The same syntax is used for this extension and the cRLDistributionPoints extension, and is described in section 4.2.1.14. The same conventions apply to both extensions.

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

FreshestCRL ::= CRLDistributionPoints

4.2.2 Private Internet Extensions

This section defines two extensions for use in the Internet Public Key Infrastructure. These extensions may be used to direct applications to on-line information about the issuing CA or the subject. As the information may be available in multiple forms, each extension is a sequence of IA5String values, each of which represents a URI. The URI implicitly specifies the location and format of the information and the method for obtaining the information.

An object identifier is defined for the private extension. The object identifier associated with the private extension is defined under the arc id-pe within the arc id-pkix. Any future extensions defined for the Internet PKI are also expected to be defined under the arc id-pe.

id-pkix OBJECT IDENTIFIER ::=

{ iso(1) identified-organization(3) dod(6) internet(1) security(5) mechanisms(5) pkix(7) }

id-pe OBJECT IDENTIFIER ::= { id-pkix 1 }

4.2.2.1 Authority Information Access

The authority information access extension indicates how to access CA information and services for the issuer of the certificate in which the extension appears. Information and services may include on-line validation services and CA policy data. (The location of CRLs is not specified in this extension; that information is provided by the cRLDistributionPoints extension.) This extension may be included in end entity or CA certificates, and it MUST be non-critical.

id-pe-authorityInfoAccess OBJECT IDENTIFIER ::= { id-pe 1 }

AuthorityInfoAccessSyntax ::=

SEQUENCE SIZE (1..MAX) OF AccessDescription

AccessDescription ::= SEQUENCE {

accessMethod OBJECT IDENTIFIER,
accessLocation GeneralName }

id-ad OBJECT IDENTIFIER ::= { id-pkix 48 }

id-ad-caIssuers OBJECT IDENTIFIER ::= { id-ad 2 }

id-ad-ocsp OBJECT IDENTIFIER ::= { id-ad 1 }

Each entry in the sequence AuthorityInfoAccessSyntax describes the format and location of additional information provided by the CA that issued the certificate in which this extension appears. The type and format of the information is specified by the accessMethod field; the accessLocation field specifies the location of the information. The retrieval mechanism may be implied by the accessMethod or specified by accessLocation.

This profile defines two accessMethod OIDs: id-ad-caIssuers and id-ad-ocsp.

The id-ad-caIssuers OID is used when the additional information lists CAs that have issued certificates superior to the CA that issued the certificate containing this extension. The referenced CA issuers description is intended to aid certificate users in the selection of a certification path that terminates at a point trusted by the certificate user.

When id-ad-caIssuers appears as accessMethod, the accessLocation field describes the referenced description server and the access protocol to obtain the referenced description. The accessLocation field is defined as a GeneralName, which can take several forms. Where the information is available via http, ftp, or ldap, accessLocation MUST be a uniformResourceIdentifier. Where the information is available via the Directory Access Protocol (DAP), accessLocation MUST be a directoryName. The entry for that directoryName contains CA certificates in the crossCertificatePair attribute. When the information is available via electronic mail, accessLocation MUST be an rfc822Name. The semantics of other id-ad-caIssuers accessLocation name forms are not defined.

The id-ad-ocsp OID is used when revocation information for the certificate containing this extension is available using the Online Certificate Status Protocol (OCSP) [RFC 2560].

When id-ad-ocsp appears as accessMethod, the accessLocation field is the location of the OCSP responder, using the conventions defined in [RFC 2560].

Additional access descriptors may be defined in other PKIX specifications.

4.2.2.2 Subject Information Access

The subject information access extension indicates how to access information and services for the subject of the certificate in which the extension appears. When the subject is a CA, information and services may include certificate validation services and CA policy data. When the subject is an end entity, the information describes the type of services offered and how to access them. In this case, the contents of this extension are defined in the protocol specifications for the suported services. This extension may be included in subject or CA certificates, and it MUST be non-critical.

id-pe-subjectInfoAccess OBJECT IDENTIFIER ::= { id-pe 11 }

SubjectInfoAccessSyntax ::=

SEQUENCE SIZE (1..MAX) OF AccessDescription

AccessDescription ::= SEQUENCE {

accessMethod OBJECT IDENTIFIER,
accessLocation GeneralName }

Each entry in the sequence SubjectInfoAccessSyntax describes the format and location of additional information provided by the subject of the certificate in which this extension appears. The type and format of the information is specified by the accessMethod field; the accessLocation field specifies the location of the information. The retrieval mechanism may be implied by the accessMethod or specified by accessLocation.

This profile defines one access method to be used when the subject is a CA, and one access method to be used when the subject is an end entity. Additional access methods may be defined in the future in the protocol specifications for other services.

The id-ad-caRepository OID is used when the subject is a CA, and publishes its certificates and CRLs (if issued) in a repository. The accessLocation field is defined as a GeneralName, which can take several forms. Where the information is available via http, ftp, or ldap, accessLocation MUST be a uniformResourceIdentifier. Where the information is available via the directory access protocol (dap), accessLocation MUST be a directoryName. When the information is available via electronic mail, accessLocation MUST be an rfc822Name. The semantics of other name forms of of accessLocation (when accessMethod is id-ad-caRepository) are not defined by this specification.

The id-ad-timeStamping OID is used when the subject offers timestamping services using the Time Stamp Protocol defined in [PKIXTSA]. Where the timestamping services are available via http or ftp, accessLocation MUST be a uniformResourceIdentifier. Where the timestamping services are available via electronic mail, accessLocation MUST be an rfc822Name. Where timestamping services are available using TCP/IP, the dNSName or ipAddress name forms may be used. The semantics of other name forms of accessLocation (when accessMethod is id-ad-timeStamping) are not defined by this specification.

Additional access descriptors may be defined in other PKIX specifications.

id-ad OBJECT IDENTIFIER ::= { id-pkix 48 }

id-ad-caRepository OBJECT IDENTIFIER ::= { id-ad 5 }

id-ad-timeStamping OBJECT IDENTIFIER ::= { id-ad 3 }


->5