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Title "X509V3_CONFIG 5" For nroff, turn off justification. Always turn off hyphenation; it makes
way too many mistakes in technical documents.
x509v3_config - X509 V3 certificate extension configuration format Header "DESCRIPTION" Several OpenSSL commands can add extensions to a certificate or certificate request based on the contents of a configuration file and \s-1CLI\s0 options such as -addext. The syntax of configuration files is described in config\|(5). The commands typically have an option to specify the name of the configuration file, and a section within that file; see the documentation of the individual command for details.

This page uses extensions as the name of the section, when needed in examples.

Each entry in the extension section takes the form:

.Vb 1 name = [critical, ]value(s) .Ve

If critical is present then the extension will be marked as critical.

If multiple entries are processed for the same extension name, later entries override earlier ones with the same name.

The format of values depends on the value of name, many have a type-value pairing where the type and value are separated by a colon. There are four main types of extension:

.Vb 4 string multi-valued raw arbitrary .Ve

Each is described in the following paragraphs.

String extensions simply have a string which contains either the value itself or how it is obtained.

Multi-valued extensions have a short form and a long form. The short form is a comma-separated list of names and values:

.Vb 1 basicConstraints = critical, CA:true, pathlen:1 .Ve

The long form allows the values to be placed in a separate section:

.Vb 2 [extensions] basicConstraints = critical, @basic_constraints \& [basic_constraints] CA = true pathlen = 1 .Ve

Both forms are equivalent.

If an extension is multi-value and a field value must contain a comma the long form must be used otherwise the comma would be misinterpreted as a field separator. For example:

.Vb 1 subjectAltName = URI:ldap://somehost.com/CN=foo,OU=bar .Ve

will produce an error but the equivalent form:

.Vb 2 [extensions] subjectAltName = @subject_alt_section \& [subject_alt_section] subjectAltName = URI:ldap://somehost.com/CN=foo,OU=bar .Ve

is valid.

OpenSSL does not support multiple occurrences of the same field within a section. In this example:

.Vb 2 [extensions] subjectAltName = @alt_section \& [alt_section] email = steve@example.com email = steve@example.org .Ve

will only recognize the last value. To specify multiple values append a numeric identifier, as shown here:

.Vb 2 [extensions] subjectAltName = @alt_section \& [alt_section] email.1 = steve@example.com email.2 = steve@example.org .Ve

The syntax of raw extensions is defined by the source code that parses the extension but should be documened. See \*(L"Certificate Policies\*(R" for an example of a raw extension.

If an extension type is unsupported, then the arbitrary extension syntax must be used, see the \*(L"\s-1ARBITRARY EXTENSIONS\*(R"\s0 section for more details.

Header "STANDARD EXTENSIONS" The following sections describe the syntax of each supported extension. They do not define the semantics of the extension. Subsection "Basic Constraints" This is a multi-valued extension which indicates whether a certificate is a \s-1CA\s0 certificate. The first value is \s-1CA\s0 followed by \s-1TRUE\s0 or \fB\s-1FALSE\s0. If \s-1CA\s0 is \s-1TRUE\s0 then an optional pathlen name followed by a nonnegative value can be included.

For example:

.Vb 1 basicConstraints = CA:TRUE \& basicConstraints = CA:FALSE \& basicConstraints = critical, CA:TRUE, pathlen:1 .Ve

A \s-1CA\s0 certificate must include the basicConstraints name with the \s-1CA\s0 parameter set to \s-1TRUE\s0. An end-user certificate must either have \s-1CA:FALSE\s0 or omit the extension entirely. The pathlen parameter specifies the maximum number of CAs that can appear below this one in a chain. A pathlen of zero means the \s-1CA\s0 cannot sign any sub-CA's, and can only sign end-entity certificates.

Subsection "Key Usage" Key usage is a multi-valued extension consisting of a list of names of the permitted key usages. The defined values are: \*(C`digitalSignature\*(C', \f(CW\*(C`nonRepudiation\*(C', \*(C`keyEncipherment\*(C', \*(C`dataEncipherment\*(C', \*(C`keyAgreement\*(C', \f(CW\*(C`keyCertSign\*(C', \*(C`cRLSign\*(C', \*(C`encipherOnly\*(C', and \*(C`decipherOnly\*(C'.

Examples:

.Vb 1 keyUsage = digitalSignature, nonRepudiation \& keyUsage = critical, keyCertSign .Ve

Subsection "Extended Key Usage" This extension consists of a list of values indicating purposes for which the certificate public key can be used. Each value can be either a short text name or an \s-1OID.\s0 The following text names, and their intended meaning, are known:

.Vb 10 Value Meaning according to RFC 5280 etc. ----- ---------------------------------- serverAuth SSL/TLS WWW Server Authentication clientAuth SSL/TLS WWW Client Authentication codeSigning Code Signing emailProtection E-mail Protection (S/MIME) timeStamping Trusted Timestamping OCSPSigning OCSP Signing ipsecIKE ipsec Internet Key Exchange msCodeInd Microsoft Individual Code Signing (authenticode) msCodeCom Microsoft Commercial Code Signing (authenticode) msCTLSign Microsoft Trust List Signing msEFS Microsoft Encrypted File System .Ve

While \s-1IETF RFC 5280\s0 says that id-kp-serverAuth and id-kp-clientAuth are only for \s-1WWW\s0 use, in practice they are used for all kinds of \s-1TLS\s0 clients and servers, and this is what OpenSSL assumes as well.

Examples:

.Vb 1 extendedKeyUsage = critical, codeSigning, 1.2.3.4 \& extendedKeyUsage = serverAuth, clientAuth .Ve

Subsection "Subject Key Identifier" The \s-1SKID\s0 extension specification has a value with three choices. If the value is the word none then no \s-1SKID\s0 extension will be included. If the value is the word hash, or by default for the x509, req, and \fBca apps, the process specified in \s-1RFC 5280\s0 section 4.2.1.2. (1) is followed: The keyIdentifier is composed of the 160-bit \s-1SHA-1\s0 hash of the value of the \s-1BIT STRING\s0 subjectPublicKey (excluding the tag, length, and number of unused bits).

Otherwise, the value must be a hex string (possibly with \*(C`:\*(C' separating bytes) to output directly, however, this is strongly discouraged.

Example:

.Vb 1 subjectKeyIdentifier = hash .Ve

Subsection "Authority Key Identifier" The \s-1AKID\s0 extension specification may have the value none indicating that no \s-1AKID\s0 shall be included. Otherwise it may have the value keyid or issuer or both of them, separated by \*(C`,\*(C'. Either or both can have the option always, indicated by putting a colon \*(C`:\*(C' between the value and this option. For self-signed certificates the \s-1AKID\s0 is suppressed unless always is present. By default the x509, req, and ca apps behave as if \*(L"none\*(R" was given for self-signed certificates and \*(L"keyid, issuer\*(R" otherwise.

If keyid is present, an attempt is made to copy the subject key identifier (\s-1SKID\s0) from the issuer certificate except if the issuer certificate is the same as the current one and it is not self-signed. The hash of the public key related to the signing key is taken as fallback if the issuer certificate is the same as the current certificate. If always is present but no value can be obtained, an error is returned.

If issuer is present, and in addition it has the option always specified or keyid is not present, then the issuer \s-1DN\s0 and serial number are copied from the issuer certificate.

Examples:

.Vb 1 authorityKeyIdentifier = keyid, issuer \& authorityKeyIdentifier = keyid, issuer:always .Ve

Subsection "Subject Alternative Name" This is a multi-valued extension that supports several types of name identifier, including \fBemail (an email address), \fB\s-1URI\s0 (a uniform resource indicator), \fB\s-1DNS\s0 (a \s-1DNS\s0 domain name), \fB\s-1RID\s0 (a registered \s-1ID: OBJECT IDENTIFIER\s0), \fB\s-1IP\s0 (an \s-1IP\s0 address), \fBdirName (a distinguished name), and otherName. The syntax of each is described in the following paragraphs.

The email option has two special values. \f(CW\*(C`copy\*(C' will automatically include any email addresses contained in the certificate subject name in the extension. \f(CW\*(C`move\*(C' will automatically move any email addresses from the certificate subject name to the extension.

The \s-1IP\s0 address used in the \s-1IP\s0 option can be in either IPv4 or IPv6 format.

The value of dirName is specifies the configuration section containing the distinguished name to use, as a set of name-value pairs. Multi-valued AVAs can be formed by prefacing the name with a + character.

The value of otherName can include arbitrary data associated with an \s-1OID\s0; the value should be the \s-1OID\s0 followed by a semicolon and the content in specified using the syntax in ASN1_generate_nconf\|(3).

Examples:

.Vb 1 subjectAltName = email:copy, email:my@example.com, URI:http://my.example.com/ \& subjectAltName = IP:192.168.7.1 \& subjectAltName = IP:13::17 \& subjectAltName = email:my@example.com, RID:1.2.3.4 \& subjectAltName = otherName:1.2.3.4;UTF8:some other identifier \& [extensions] subjectAltName = dirName:dir_sect \& [dir_sect] C = UK O = My Organization OU = My Unit CN = My Name .Ve

Non-ASCII Email Address conforming the syntax defined in Section 3.3 of \s-1RFC 6531\s0 are provided as otherName.SmtpUTF8Mailbox. According to \s-1RFC 8398,\s0 the email address should be provided as UTF8String. To enforce the valid representation in the certificate, the SmtpUTF8Mailbox should be provided as follows

.Vb 3 subjectAltName=@alts [alts] otherName = 1.3.6.1.5.5.7.8.9;FORMAT:UTF8,UTF8String:nonasciiname.example.com .Ve

Subsection "Issuer Alternative Name" This extension supports most of the options of subject alternative name; it does not support email:copy. It also adds issuer:copy as an allowed value, which copies any subject alternative names from the issuer certificate, if possible.

Example:

.Vb 1 issuerAltName = issuer:copy .Ve

Subsection "Authority Info Access" This extension gives details about how to retrieve information that related to the certificate that the \s-1CA\s0 makes available. The syntax is \fBaccess_id;location, where access_id is an object identifier (although only a few values are well-known) and location has the same syntax as subject alternative name (except that email:copy is not supported).

Possible values for access_id include \s-1OCSP\s0 (\s-1OCSP\s0 responder), \fBcaIssuers (\s-1CA\s0 Issuers), \fBad_timestamping (\s-1AD\s0 Time Stamping), \fB\s-1AD_DVCS\s0 (ad dvcs), \fBcaRepository (\s-1CA\s0 Repository).

Examples:

.Vb 1 authorityInfoAccess = OCSP;URI:http://ocsp.example.com/,caIssuers;URI:http://myca.example.com/ca.cer \& authorityInfoAccess = OCSP;URI:http://ocsp.example.com/ .Ve

Subsection "CRL distribution points" This is a multi-valued extension whose values can be either a name-value pair using the same form as subject alternative name or a single value specifying the section name containing all the distribution point values.

When a name-value pair is used, a DistributionPoint extension will be set with the given value as the fullName field as the distributionPoint value, and the reasons and cRLIssuer fields will be omitted.

When a single option is used, the value specifies the section, and that section can have the following items:

Item "fullname" The full name of the distribution point, in the same format as the subject alternative name. Item "relativename" The value is taken as a distinguished name fragment that is set as the value of the nameRelativeToCRLIssuer field. Item "CRLIssuer" The value must in the same format as the subject alternative name. Item "reasons" A multi-value field that contains the reasons for revocation. The recognized values are: \*(C`keyCompromise\*(C', \*(C`CACompromise\*(C', \*(C`affiliationChanged\*(C', \f(CW\*(C`superseded\*(C', \*(C`cessationOfOperation\*(C', \*(C`certificateHold\*(C', \f(CW\*(C`privilegeWithdrawn\*(C', and \*(C`AACompromise\*(C'.

Only one of fullname or relativename should be specified.

Simple examples:

.Vb 1 crlDistributionPoints = URI:http://example.com/myca.crl \& crlDistributionPoints = URI:http://example.com/myca.crl, URI:http://example.org/my.crl .Ve

Full distribution point example:

.Vb 2 [extensions] crlDistributionPoints = crldp1_section \& [crldp1_section] fullname = URI:http://example.com/myca.crl CRLissuer = dirName:issuer_sect reasons = keyCompromise, CACompromise \& [issuer_sect] C = UK O = Organisation CN = Some Name .Ve

Subsection "Issuing Distribution Point" This extension should only appear in CRLs. It is a multi-valued extension whose syntax is similar to the \*(L"section\*(R" pointed to by the \s-1CRL\s0 distribution points extension. The following names have meaning: Item "fullname" The full name of the distribution point, in the same format as the subject alternative name. Item "relativename" The value is taken as a distinguished name fragment that is set as the value of the nameRelativeToCRLIssuer field. Item "onlysomereasons" A multi-value field that contains the reasons for revocation. The recognized values are: \*(C`keyCompromise\*(C', \*(C`CACompromise\*(C', \*(C`affiliationChanged\*(C', \f(CW\*(C`superseded\*(C', \*(C`cessationOfOperation\*(C', \*(C`certificateHold\*(C', \f(CW\*(C`privilegeWithdrawn\*(C', and \*(C`AACompromise\*(C'. Item "onlyuser, onlyCA, onlyAA, indirectCRL" The value for each of these names is a boolean.

Example:

.Vb 2 [extensions] issuingDistributionPoint = critical, @idp_section \& [idp_section] fullname = URI:http://example.com/myca.crl indirectCRL = TRUE onlysomereasons = keyCompromise, CACompromise .Ve

Subsection "Certificate Policies" This is a raw extension that supports all of the defined fields of the certificate extension.

Policies without qualifiers are specified by giving the \s-1OID.\s0 Multiple policies are comma-separated. For example:

.Vb 1 certificatePolicies = 1.2.4.5, 1.1.3.4 .Ve

To include policy qualifiers, use the \*(L"@section\*(R" syntax to point to a section that specifies all the information.

The section referred to must include the policy \s-1OID\s0 using the name \fBpolicyIdentifier. cPSuri qualifiers can be included using the syntax:

.Vb 1 CPS.nnn = value .Ve

where \*(C`nnn\*(C' is a number.

userNotice qualifiers can be set using the syntax:

.Vb 1 userNotice.nnn = @notice .Ve

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, noticeNumbers is a comma separated list of numbers. The organization and noticeNumbers options (if included) must \s-1BOTH\s0 be present. Some software might require the ia5org option at the top level; this changes the encoding from Displaytext to IA5String.

Example:

.Vb 2 [extensions] certificatePolicies = ia5org, 1.2.3.4, 1.5.6.7.8, @polsect \& [polsect] policyIdentifier = 1.3.5.8 CPS.1 = "http://my.host.example.com/" CPS.2 = "http://my.your.example.com/" userNotice.1 = @notice \& [notice] explicitText = "Explicit Text Here" organization = "Organisation Name" noticeNumbers = 1, 2, 3, 4 .Ve

The character encoding of explicitText can be specified by prefixing the value with \s-1UTF8\s0, \s-1BMP\s0, or \s-1VISIBLE\s0 followed by colon. For example:

.Vb 2 [notice] explicitText = "UTF8:Explicit Text Here" .Ve

Subsection "Policy Constraints" This is a multi-valued extension which consisting of the names \fBrequireExplicitPolicy or inhibitPolicyMapping and a non negative integer value. At least one component must be present.

Example:

.Vb 1 policyConstraints = requireExplicitPolicy:3 .Ve

Subsection "Inhibit Any Policy" This is a string extension whose value must be a non negative integer.

Example:

.Vb 1 inhibitAnyPolicy = 2 .Ve

Subsection "Name Constraints" This is a multi-valued extension. The name should begin with the word permitted or excluded followed by a ;. The rest of the name and the value follows the syntax of subjectAltName except \fBemail:copy is not supported and the \s-1IP\s0 form should consist of an \s-1IP\s0 addresses and subnet mask separated by a /.

Examples:

.Vb 1 nameConstraints = permitted;IP:192.168.0.0/255.255.0.0 \& nameConstraints = permitted;email:.example.com \& nameConstraints = excluded;email:.com .Ve

Subsection "OCSP No Check" This is a string extension. It is parsed, but ignored.

Example:

.Vb 1 noCheck = ignored .Ve

Subsection "TLS Feature (aka Must Staple)" This is a multi-valued extension consisting of a list of \s-1TLS\s0 extension identifiers. Each identifier may be a number (0..65535) or a supported name. When a \s-1TLS\s0 client sends a listed extension, the \s-1TLS\s0 server is expected to include that extension in its reply.

The supported names are: status_request and status_request_v2.

Example:

.Vb 1 tlsfeature = status_request .Ve

Header "DEPRECATED EXTENSIONS" The following extensions are non standard, Netscape specific and largely obsolete. Their use in new applications is discouraged. Subsection "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. Other extensions of this type are: nsBaseUrl, \fBnsRevocationUrl, nsCaRevocationUrl, nsRenewalUrl, nsCaPolicyUrl and nsSslServerName. Subsection "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, \fBobjsign, reserved, sslCA, emailCA, objCA.

Header "ARBITRARY EXTENSIONS" If an extension is not supported by the OpenSSL code then it must be encoded using the arbitrary extension format. It is also possible to use the arbitrary format for supported extensions. Extreme care should be taken to ensure that the data is formatted correctly for the given extension type.

There are two ways to encode arbitrary extensions.

The first way is to use the word \s-1ASN1\s0 followed by the extension content using the same syntax as ASN1_generate_nconf\|(3). For example:

.Vb 3 [extensions] 1.2.3.4 = critical, ASN1:UTF8String:Some random data 1.2.3.4.1 = ASN1:SEQUENCE:seq_sect \& [seq_sect] field1 = UTF8:field1 field2 = UTF8:field2 .Ve

It is also possible to use the word \s-1DER\s0 to include the raw encoded data in any extension.

.Vb 2 1.2.3.4 = critical, DER:01:02:03:04 1.2.3.4.1 = DER:01020304 .Ve

The value following \s-1DER\s0 is a hex dump of the \s-1DER\s0 encoding of the extension Any extension can be placed in this form to override the default behaviour. For example:

.Vb 1 basicConstraints = critical, DER:00:01:02:03 .Ve

Header "WARNINGS" There is no guarantee that a specific implementation will process a given extension. It may therefore be sometimes possible to use certificates for purposes prohibited by their extensions because a specific application does not recognize or honour the values of the relevant extensions.

The \s-1DER\s0 and \s-1ASN1\s0 options should be used with caution. It is possible to create invalid extensions if they are not used carefully.

Header "SEE ALSO" \fBopenssl-req\|(1), openssl-ca\|(1), openssl-x509\|(1), \fBASN1_generate_nconf\|(3) Header "COPYRIGHT" Copyright 2004-2021 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the Apache License 2.0 (the \*(L"License\*(R"). You may not use this file except in compliance with the License. You can obtain a copy in the file \s-1LICENSE\s0 in the source distribution or at <https://www.openssl.org/source/license.html>.