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Basic constraints

This is a multi-valued extension which indicates whether a certificate is a CA certificate. The first (mandatory) name is CA followed by TRUE or FALSE. If CA is TRUE, then an optional pathlen name followed by a non-negative value can be included. For example:

basicConstraints=CA:TRUE
basicConstraints=CA:FALSE
basicConstraints=critical,CA:TRUE, pathlen:0

A CA certificate must include the basicConstraints value with the CA field set to TRUE. An end user certificate must either set CA to FALSE or exclude the extension entirely. Some software may require the inclusion of basicConstraints with CA set to FALSE for end entity certificates.

The pathlen parameter indicates the maximum number of CAs that can appear below this one in a chain. So if you have a CA with a pathlen of zero, it can only be used to sign end user certificates and not further CAs.

Key usage

Key usage is a multi-valued extension consisting of a list of names of the permitted key usages.

The supported names are: digitalSignature, nonRepudiation, keyEncipherment, dataEncipherment, keyAgreement, keyCertSign, cRLSign, encipherOnly, and decipherOnly. Examples:

keyUsage=digitalSignature, nonRepudiation
keyUsage=critical, keyCertSign

Extended key usage

This extension consists of a list of purposes for which the certificate public key can be used.

These can either be object short names or the dotted numerical form of OIDs. While any OID can be used, only certain values make sense. In particular the following PKIX, NS and MS values are meaningful:

Examples:

extendedKeyUsage=critical,codeSigning,1.2.3.4
extendedKeyUsage=serverAuth,clientAuth

Subject key identifier

This is really a string extension and can take two possible values. Either the word hash which will automatically follow the guidelines in RFC 3280 or a hex string giving the extension value to include. The use of the hex string is strongly discouraged. Example:

Authority key identifier

The authority key identifier extension permits two options, keyid and issuer: both can take the optional value always.

If the keyid option is present, an attempt is made to copy the subject key identifier from the parent certificate. If the value always is present, then an error is returned if the option fails.

The issuer option copies the issuer and serial number from the issuer certificate. This will only be done if the keyid option fails or is not included unless the always flag will always include the value. Example:

Subject alternative name

The subject alternative name extension allows various literal values to be included in the configuration file. These include email (an email address), URI (a uniform resource indicator), DNS (a DNS domain name), RID (a registered ID: OBJECT IDENTIFIER), IP (an IP address), dirName (a distinguished name), and otherName.

The email option can include a special copy value. This will automatically include any email addresses contained in the certificate subject name in the extension.

The IP address used in the IP options can be in either IPv4 or IPv6 format.

The value of dirName should point to a section containing the distinguished name to use as a set of name value pairs. Multi values AVAs can be formed by prefacing the name with a ‘+’ character.

otherName can include arbitrary data associated with an OID: the value should be the OID followed by a semicolon and the content in standard ASN1_generate_nconf(3) format. Examples:

subjectAltName=email:copy,email:[email protected],URI:http://my.url.here/
subjectAltName=IP:192.168.7.1
subjectAltName=IP:13::17
subjectAltName=email:[email protected],RID:1.2.3.4
subjectAltName=otherName:1.2.3.4;UTF8:some other identifier

subjectAltName=dirName:dir_sect

[dir_sect]
C=UK
O=My Organization
OU=My Unit
CN=My Name

Issuer alternative name

The issuer alternative name option supports all the literal options of subject alternative name. It does not support the email:copy option because that would not make sense. It does support an additional issuer:copy option that will copy all the subject alternative name values from the issuer certificate (if possible). Example:

Authority info access

The authority information access extension gives details about how to access certain information relating to the CA. Its syntax is accessOID; location where location has the same syntax as subject alternative name (except that email:copy is not supported). accessOID can be any valid OID but only certain values are meaningful, for example OCSP and caIssuers. Example:

authorityInfoAccess = OCSP;URI:http://ocsp.my.host/
authorityInfoAccess = caIssuers;URI:http://my.ca/ca.html

CRL distribution points

This is a multi-valued extension whose options can be either in name:value pair form using the same form as subject alternative name or a single value representing a section name containing all the distribution point fields.

For a name:value pair a new DistributionPoint with the fullName field set to the given value, both the cRLissuer and reasons fields are omitted in this case.

In the single option case, the section indicated contains values for each field. In this section:

If the name is fullname, the value field should contain the full name of the distribution point in the same format as subject alternative name.

If the name is relativename, then the value field should contain a section name whose contents represent a DN fragment to be placed in this field.

The name CRLIssuer, if present, should contain a value for this field in subject alternative name format.

If the name is reasons, the value field should consist of a comma separated field containing the reasons. Valid reasons are: keyCompromise, CACompromise, affiliationChanged, superseded, cessationOfOperation, certificateHold, privilegeWithdrawn, and AACompromise.

Simple examples:

crlDistributionPoints=URI:http://myhost.com/myca.crl
crlDistributionPoints=URI:http://my.com/my.crl,URI:http://oth.com/my.crl

Full distribution point example:

crlDistributionPoints=crldp1_section

[crldp1_section]
fullname=URI:http://myhost.com/myca.crl
CRLissuer=dirName:issuer_sect
reasons=keyCompromise, CACompromise

[issuer_sect]
C=UK
O=Organisation
CN=Some Name

Issuing distribution point

This extension should only appear in CRLs. It is a multi-valued extension whose syntax is similar to the "section" pointed to by the CRL distribution points extension with a few differences.

The names reasons and CRLissuer are not recognized.

The name onlysomereasons is accepted, which sets this field. The value is in the same format as the CRL distribution point reasons field.

The names onlyuser, onlyCA, onlyAA, and indirectCRL are also accepted. The values should be a boolean values (TRUE or FALSE) to indicate the value of the corresponding field. Example:

issuingDistributionPoint=critical, @idp_section

[idp_section]
fullname=URI:http://myhost.com/myca.crl
indirectCRL=TRUE
onlysomereasons=keyCompromise, CACompromise

[issuer_sect]
C=UK
O=Organisation
CN=Some Name

Certificate policies

This is a raw extension. All the fields of this extension can be set by using the appropriate syntax.

If you follow the PKIX recommendations and just use one OID, then you just include the value of that OID. Multiple OIDs can be set separated by commas, for example:

If you wish to include qualifiers, then the policy OID and qualifiers need to be specified in a separate section: this is done by using the @section syntax instead of a literal OID value.

The section referred to must include the policy OID using the name policyIdentifier. CPSuri qualifiers can be included using the syntax:

userNotice qualifiers can be set using the syntax:

The value of the userNotice qualifier is specified in the relevant section. This section can include explicitText, organization, and noticeNumbers options. explicitText and organization are text strings, and noticeNumbers is a comma separated list of numbers. The organization and noticeNumbers options (if included) must both be present. If you use the userNotice option with IE5 then you need the ia5org option at the top level to modify the encoding: otherwise it will not be interpreted properly. Example:

certificatePolicies=ia5org,1.2.3.4,1.5.6.7.8,@polsect

[polsect]
policyIdentifier = 1.3.5.8
CPS.1="http://my.host.name/"
CPS.2="http://my.your.name/"
userNotice.1=@notice

[notice]
explicitText="Explicit Text Here"
organization="Organisation Name"
noticeNumbers=1,2,3,4

The ia5org option changes the type of the organization field. In RFC 2459, it can only be of type DisplayText. In RFC 3280, IA5String is also permissible. Some software (for example some versions of MSIE) may require ia5org.

Policy constraints

This is a multi-valued extension which consists of the names requireExplicitPolicy or inhibitPolicyMapping and a non-negative integer value. At least one component must be present. Example:

Inhibit any policy

This is a string extension whose value must be a non-negative integer. Example:

Name constraints

The name constraints extension is a multi-valued extension. The name should begin with the word permitted or excluded, followed by a semicolon. The rest of the name and the value follows the syntax of subjectAltName except email:copy is not supported and the IP form should consist of an IP addresses and subnet mask separated by a slash. Examples:

nameConstraints=permitted;IP:192.168.0.0/255.255.0.0
nameConstraints=permitted;email:.somedomain.com
nameConstraints=excluded;email:.com

OCSP no check

The OCSP no check extension is a string extension, but its value is ignored. Example:

TLS Feature (aka must staple)

This is a multi-valued extension consisting of a list of TLS extension identifiers. Each identifier may be a number in the range from 0 to 65535 or a supported name. When a TLS client sends a listed extension, the TLS server is expected to include that extension in its reply.

The supported names are: status_request and status_request_v2. Example:

Netscape string extensions

Netscape comment (nsComment) is a string extension containing a comment which will be displayed when the certificate is viewed in some browsers. Example:

Other supported extensions in this category are: nsBaseUrl, nsRevocationUrl, nsCaRevocationUrl, nsRenewalUrl, nsCaPolicyUrl, and nsSslServerName.

Netscape certificate type

This is a multi-valued extensions which consists of a list of flags to be included. It was used to indicate the purposes for which a certificate could be used. The basicConstraints, keyUsage, and extended key usage extensions are now used instead.

Acceptable values for nsCertType are: client, server, email, objsign, reserved, sslCA, emailCA, objCA.