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=for comment openssl_manual_section:5
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x509v3_config - X509 V3 certificate extension configuration format
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Several of the OpenSSL utilities can add extensions to a certificate or
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certificate request based on the contents of a configuration file.
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Typically the application will contain an option to point to an extension
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section. Each line of the extension section takes the form:
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extension_name=[critical,] extension_options
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If B<critical> is present then the extension will be critical.
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The format of B<extension_options> depends on the value of B<extension_name>.
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There are four main types of extension: I<string> extensions, I<multi-valued>
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extensions, I<raw> and I<arbitrary> extensions.
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String extensions simply have a string which contains either the value itself
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or how it is obtained.
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nsComment="This is a Comment"
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Multi-valued extensions have a short form and a long form. The short form
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is a list of names and values:
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basicConstraints=critical,CA:true,pathlen:1
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The long form allows the values to be placed in a separate section:
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basicConstraints=critical,@bs_section
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Both forms are equivalent.
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The syntax of raw extensions is governed by the extension code: it can
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for example contain data in multiple sections. The correct syntax to
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use is defined by the extension code itself: check out the certificate
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policies extension for an example.
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If an extension type is unsupported then the I<arbitrary> extension syntax
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must be used, see the L<ARBITRARY EXTENSIONS|/"ARBITRARY EXTENSIONS"> section for more details.
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=head1 STANDARD EXTENSIONS
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The following sections describe each supported extension in detail.
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=head2 Basic Constraints.
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This is a multi valued extension which indicates whether a certificate is
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a CA certificate. The first (mandatory) name is B<CA> followed by B<TRUE> or
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B<FALSE>. If B<CA> is B<TRUE> then an optional B<pathlen> name followed by an
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non-negative value can be included.
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basicConstraints=CA:TRUE
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basicConstraints=CA:FALSE
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basicConstraints=critical,CA:TRUE, pathlen:0
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A CA certificate B<must> include the basicConstraints value with the CA field
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set to TRUE. An end user certificate must either set CA to FALSE or exclude the
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extension entirely. Some software may require the inclusion of basicConstraints
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with CA set to FALSE for end entity certificates.
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The pathlen parameter indicates the maximum number of CAs that can appear
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below this one in a chain. So if you have a CA with a pathlen of zero it can
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only be used to sign end user certificates and not further CAs.
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Key usage is a multi valued extension consisting of a list of names of the
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The supporte names are: digitalSignature, nonRepudiation, keyEncipherment,
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dataEncipherment, keyAgreement, keyCertSign, cRLSign, encipherOnly
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keyUsage=digitalSignature, nonRepudiation
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keyUsage=critical, keyCertSign
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=head2 Extended Key Usage.
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This extensions consists of a list of usages indicating purposes for which
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the certificate public key can be used for,
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These can either be object short names or the dotted numerical form of OIDs.
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While any OID can be used only certain values make sense. In particular the
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following PKIX, NS and MS values are meaningful:
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serverAuth SSL/TLS Web Server Authentication.
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clientAuth SSL/TLS Web Client Authentication.
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codeSigning Code signing.
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emailProtection E-mail Protection (S/MIME).
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timeStamping Trusted Timestamping
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msCodeInd Microsoft Individual Code Signing (authenticode)
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msCodeCom Microsoft Commercial Code Signing (authenticode)
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msCTLSign Microsoft Trust List Signing
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msSGC Microsoft Server Gated Crypto
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msEFS Microsoft Encrypted File System
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nsSGC Netscape Server Gated Crypto
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extendedKeyUsage=critical,codeSigning,1.2.3.4
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extendedKeyUsage=nsSGC,msSGC
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=head2 Subject Key Identifier.
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This is really a string extension and can take two possible values. Either
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the word B<hash> which will automatically follow the guidelines in RFC3280
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or a hex string giving the extension value to include. The use of the hex
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string is strongly discouraged.
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subjectKeyIdentifier=hash
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=head2 Authority Key Identifier.
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The authority key identifier extension permits two options. keyid and issuer:
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both can take the optional value "always".
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If the keyid option is present an attempt is made to copy the subject key
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identifier from the parent certificate. If the value "always" is present
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then an error is returned if the option fails.
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The issuer option copies the issuer and serial number from the issuer
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certificate. This will only be done if the keyid option fails or
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is not included unless the "always" flag will always include the value.
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authorityKeyIdentifier=keyid,issuer
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=head2 Subject Alternative Name.
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The subject alternative name extension allows various literal values to be
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included in the configuration file. These include B<email> (an email address)
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B<URI> a uniform resource indicator, B<DNS> (a DNS domain name), B<RID> (a
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registered ID: OBJECT IDENTIFIER), B<IP> (an IP address), B<dirName>
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(a distinguished name) and otherName.
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The email option include a special 'copy' value. This will automatically
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include and email addresses contained in the certificate subject name in
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The IP address used in the B<IP> options can be in either IPv4 or IPv6 format.
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The value of B<dirName> should point to a section containing the distinguished
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name to use as a set of name value pairs. Multi values AVAs can be formed by
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prefacing the name with a B<+> character.
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otherName can include arbitrary data associated with an OID: the value
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should be the OID followed by a semicolon and the content in standard
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L<ASN1_generate_nconf(3)|ASN1_generate_nconf(3)> format.
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subjectAltName=email:copy,email:my@other.address,URI:http://my.url.here/
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subjectAltName=IP:192.168.7.1
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subjectAltName=IP:13::17
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subjectAltName=email:my@other.address,RID:1.2.3.4
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subjectAltName=otherName:1.2.3.4;UTF8:some other identifier
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subjectAltName=dirName:dir_sect
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=head2 Issuer Alternative Name.
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The issuer alternative name option supports all the literal options of
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subject alternative name. It does B<not> support the email:copy option because
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that would not make sense. It does support an additional issuer:copy option
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that will copy all the subject alternative name values from the issuer
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certificate (if possible).
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issuserAltName = issuer:copy
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=head2 Authority Info Access.
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The authority information access extension gives details about how to access
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certain information relating to the CA. Its syntax is accessOID;location
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where I<location> has the same syntax as subject alternative name (except
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that email:copy is not supported). accessOID can be any valid OID but only
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certain values are meaningful, for example OCSP and caIssuers.
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authorityInfoAccess = OCSP;URI:http://ocsp.my.host/
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authorityInfoAccess = caIssuers;URI:http://my.ca/ca.html
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=head2 CRL distribution points.
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This is a multi-valued extension whose options can be either in name:value pair
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using the same form as subject alternative name or a single value representing
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a section name containing all the distribution point fields.
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For a name:value pair a new DistributionPoint with the fullName field set to
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the given value both the cRLissuer and reasons fields are omitted in this case.
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In the single option case the section indicated contains values for each
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field. In this section:
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If the name is "fullname" the value field should contain the full name
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of the distribution point in the same format as subject alternative name.
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If the name is "relativename" then the value field should contain a section
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name whose contents represent a DN fragment to be placed in this field.
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The name "CRLIssuer" if present should contain a value for this field in
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subject alternative name format.
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If the name is "reasons" the value field should consist of a comma
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separated field containing the reasons. Valid reasons are: "keyCompromise",
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"CACompromise", "affiliationChanged", "superseded", "cessationOfOperation",
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"certificateHold", "privilegeWithdrawn" and "AACompromise".
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crlDistributionPoints=URI:http://myhost.com/myca.crl
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crlDistributionPoints=URI:http://my.com/my.crl,URI:http://oth.com/my.crl
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Full distribution point example:
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crlDistributionPoints=crldp1_section
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fullname=URI:http://myhost.com/myca.crl
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CRLissuer=dirName:issuer_sect
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reasons=keyCompromise, CACompromise
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=head2 Issuing Distribution Point
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This extension should only appear in CRLs. It is a multi valued extension
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whose syntax is similar to the "section" pointed to by the CRL distribution
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points extension with a few differences.
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The names "reasons" and "CRLissuer" are not recognized.
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The name "onlysomereasons" is accepted which sets this field. The value is
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in the same format as the CRL distribution point "reasons" field.
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The names "onlyuser", "onlyCA", "onlyAA" and "indirectCRL" are also accepted
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the values should be a boolean value (TRUE or FALSE) to indicate the value of
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the corresponding field.
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issuingDistributionPoint=critical, @idp_section
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fullname=URI:http://myhost.com/myca.crl
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onlysomereasons=keyCompromise, CACompromise
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=head2 Certificate Policies.
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This is a I<raw> extension. All the fields of this extension can be set by
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using the appropriate syntax.
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If you follow the PKIX recommendations and just using one OID then you just
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include the value of that OID. Multiple OIDs can be set separated by commas,
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certificatePolicies= 1.2.4.5, 1.1.3.4
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If you wish to include qualifiers then the policy OID and qualifiers need to
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be specified in a separate section: this is done by using the @section syntax
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instead of a literal OID value.
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The section referred to must include the policy OID using the name
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policyIdentifier, cPSuri qualifiers can be included using the syntax:
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userNotice qualifiers can be set using the syntax:
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userNotice.nnn=@notice
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The value of the userNotice qualifier is specified in the relevant section.
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This section can include explicitText, organization and noticeNumbers
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options. explicitText and organization are text strings, noticeNumbers is a
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comma separated list of numbers. The organization and noticeNumbers options
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(if included) must BOTH be present. If you use the userNotice option with IE5
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then you need the 'ia5org' option at the top level to modify the encoding:
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otherwise it will not be interpreted properly.
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certificatePolicies=ia5org,1.2.3.4,1.5.6.7.8,@polsect
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policyIdentifier = 1.3.5.8
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CPS.1="http://my.host.name/"
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CPS.2="http://my.your.name/"
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explicitText="Explicit Text Here"
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organization="Organisation Name"
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noticeNumbers=1,2,3,4
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The B<ia5org> option changes the type of the I<organization> field. In RFC2459
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it can only be of type DisplayText. In RFC3280 IA5Strring is also permissible.
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Some software (for example some versions of MSIE) may require ia5org.
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=head2 Policy Constraints
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This is a multi-valued extension which consisting of the names
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B<requireExplicitPolicy> or B<inhibitPolicyMapping> and a non negative intger
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value. At least one component must be present.
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policyConstraints = requireExplicitPolicy:3
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=head2 Inhibit Any Policy
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This is a string extension whose value must be a non negative integer.
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=head2 Name Constraints
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The name constraints extension is a multi-valued extension. The name should
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begin with the word B<permitted> or B<excluded> followed by a B<;>. The rest of
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the name and the value follows the syntax of subjectAltName except email:copy
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is not supported and the B<IP> form should consist of an IP addresses and
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subnet mask separated by a B</>.
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nameConstraints=permitted;IP:192.168.0.0/255.255.0.0
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nameConstraints=permitted;email:.somedomain.com
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nameConstraints=excluded;email:.com
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The OCSP No Check extension is a string extension but its value is ignored.
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=head1 DEPRECATED EXTENSIONS
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The following extensions are non standard, Netscape specific and largely
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obsolete. Their use in new applications is discouraged.
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=head2 Netscape String extensions.
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Netscape Comment (B<nsComment>) is a string extension containing a comment
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which will be displayed when the certificate is viewed in some browsers.
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nsComment = "Some Random Comment"
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Other supported extensions in this category are: B<nsBaseUrl>,
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B<nsRevocationUrl>, B<nsCaRevocationUrl>, B<nsRenewalUrl>, B<nsCaPolicyUrl>
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and B<nsSslServerName>.
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=head2 Netscape Certificate Type
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This is a multi-valued extensions which consists of a list of flags to be
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included. It was used to indicate the purposes for which a certificate could
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be used. The basicConstraints, keyUsage and extended key usage extensions are
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Acceptable values for nsCertType are: B<client>, B<server>, B<email>,
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B<objsign>, B<reserved>, B<sslCA>, B<emailCA>, B<objCA>.
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=head1 ARBITRARY EXTENSIONS
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If an extension is not supported by the OpenSSL code then it must be encoded
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using the arbitrary extension format. It is also possible to use the arbitrary
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format for supported extensions. Extreme care should be taken to ensure that
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the data is formatted correctly for the given extension type.
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There are two ways to encode arbitrary extensions.
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The first way is to use the word ASN1 followed by the extension content
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using the same syntax as L<ASN1_generate_nconf(3)|ASN1_generate_nconf(3)>.
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1.2.3.4=critical,ASN1:UTF8String:Some random data
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1.2.3.4=ASN1:SEQUENCE:seq_sect
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It is also possible to use the word DER to include the raw encoded data in any
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1.2.3.4=critical,DER:01:02:03:04
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The value following DER is a hex dump of the DER encoding of the extension
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Any extension can be placed in this form to override the default behaviour.
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basicConstraints=critical,DER:00:01:02:03
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There is no guarantee that a specific implementation will process a given
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extension. It may therefore be sometimes possible to use certificates for
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purposes prohibited by their extensions because a specific application does
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not recognize or honour the values of the relevant extensions.
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The DER and ASN1 options should be used with caution. It is possible to create
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totally invalid extensions if they are not used carefully.
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If an extension is multi-value and a field value must contain a comma the long
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form must be used otherwise the comma would be misinterpreted as a field
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separator. For example:
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subjectAltName=URI:ldap://somehost.com/CN=foo,OU=bar
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will produce an error but the equivalent form:
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subjectAltName=@subject_alt_section
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[subject_alt_section]
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subjectAltName=URI:ldap://somehost.com/CN=foo,OU=bar
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Due to the behaviour of the OpenSSL B<conf> library the same field name
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can only occur once in a section. This means that:
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subjectAltName=@alt_section
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will only recognize the last value. This can be worked around by using the form:
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The X509v3 extension code was first added to OpenSSL 0.9.2.
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Policy mappings, inhibit any policy and name constraints support was added in
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The B<directoryName> and B<otherName> option as well as the B<ASN1> option
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for arbitrary extensions was added in OpenSSL 0.9.8
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L<req(1)|req(1)>, L<ca(1)|ca(1)>, L<x509(1)|x509(1)>,
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L<ASN1_generate_nconf(3)|ASN1_generate_nconf(3)>
added
removed
doc/apps/x509v3_config.pod
