=pod =head1 NAME x509v3_config - X509 V3 certificate extension configuration format =head1 DESCRIPTION Several OpenSSL commands can add extensions to a certificate or certificate request based on the contents of a configuration file and CLI options such as B<-addext>. The syntax of configuration files is described in L. 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 B as the name of the section, when needed in examples. Each entry in the extension section takes the form: name = [critical, ]value(s) If B 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 B depends on the value of B, many have a type-value pairing where the type and value are separated by a colon. There are four main types of extension: string multi-valued raw arbitrary 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: basicConstraints = critical, CA:true, pathlen:1 The long form allows the values to be placed in a separate section: [extensions] basicConstraints = critical, @basic_constraints [basic_constraints] CA = true pathlen = 1 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: subjectAltName = URI:ldap://somehost.com/CN=foo,OU=bar will produce an error but the equivalent form: [extensions] subjectAltName = @subject_alt_section [subject_alt_section] subjectAltName = URI:ldap://somehost.com/CN=foo,OU=bar is valid. OpenSSL does not support multiple occurrences of the same field within a section. In this example: [extensions] subjectAltName = @alt_section [alt_section] email = steve@example.com email = steve@example.org will only recognize the last value. To specify multiple values append a numeric identifier, as shown here: [extensions] subjectAltName = @alt_section [alt_section] email.1 = steve@example.com email.2 = steve@example.org The syntax of raw extensions is defined by the source code that parses the extension but should be documented. See L for an example of a raw extension. If an extension type is unsupported, then the I extension syntax must be used, see the L section for more details. =head1 STANDARD EXTENSIONS The following sections describe the syntax of each supported extension. They do not define the semantics of the extension. =head2 Basic Constraints This is a multi-valued extension which indicates whether a certificate is a CA certificate. The first value is B followed by B or B. If B is B then an optional B name followed by a nonnegative value can be included. For example: basicConstraints = CA:TRUE basicConstraints = CA:FALSE basicConstraints = critical, CA:TRUE, pathlen:1 A CA certificate I include the B name with the B parameter set to B. An end-user certificate must either have B or omit the extension entirely. The B parameter specifies the maximum number of CAs that can appear below this one in a chain. A B of zero means the CA cannot sign any sub-CA's, and can only sign end-entity certificates. =head2 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, C, C, C, C, C, C, C, and C. Examples: keyUsage = digitalSignature, nonRepudiation keyUsage = critical, keyCertSign =head2 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 OID. The following text names, and their intended meaning, are known: 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 While IETF RFC 5280 says that B and B are only for WWW use, in practice they are used for all kinds of TLS clients and servers, and this is what OpenSSL assumes as well. Examples: extendedKeyUsage = critical, codeSigning, 1.2.3.4 extendedKeyUsage = serverAuth, clientAuth =head2 Subject Key Identifier The SKID extension specification has a value with three choices. =over 4 =item B No SKID extension will be included. =item B The process specified in RFC 5280 section 4.2.1.2. (1) is followed: The keyIdentifier is composed of the 160-bit SH

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mma-separated. For example: certificatePolicies = 1.2.4.5, 1.1.3.4 To include policy qualifiers, use the "@section" syntax to point to a section that specifies all the information. The section referred to must include the policy OID using the name B. cPSuri qualifiers can be included using the syntax: CPS.nnn = value where C is a number. userNotice qualifiers can be set using the syntax: userNotice.nnn = @notice The value of the userNotice qualifier is specified in the relevant section. This section can include B, B, and B options. explicitText and organization are text strings, noticeNumbers is a comma separated list of numbers. The organization and noticeNumbers options (if included) must BOTH be present. Some software might require the B option at the top level; this changes the encoding from Displaytext to IA5String. Example: [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 The character encoding of explicitText can be specified by prefixing the value with B, B, or B followed by colon. For example: [notice] explicitText = "UTF8:Explicit Text Here" =head2 Policy Constraints This is a multi-valued extension which consisting of the names B or B and a non negative integer value. At least one component must be present. Example: policyConstraints = requireExplicitPolicy:3 =head2 Inhibit Any Policy This is a string extension whose value must be a non negative integer. Example: inhibitAnyPolicy = 2 =head2 Name Constraints This is a multi-valued extension. The name should begin with the word B or B followed by a B<;>. The rest of the name and the value follows the syntax of subjectAltName except B is not supported and the B form should consist of an IP addresses and subnet mask separated by a B. Examples: nameConstraints = permitted;IP:192.168.0.0/255.255.0.0 nameConstraints = permitted;email:.example.com nameConstraints = excluded;email:.com =head2 OCSP No Check This is a string extension. It is parsed, but ignored. Example: noCheck = ignored =head2 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 (0..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: B and B. Example: tlsfeature = status_request =head1 DEPRECATED EXTENSIONS The following extensions are non standard, Netscape specific and largely obsolete. Their use in new applications is discouraged. =head2 Netscape String extensions Netscape Comment (B) 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: B, B, B, B, B and B. =head2 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: B, B, B, B, B, B, B, B. =head1 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 ASN1 followed by the extension content using the same syntax as L. For example: [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 It is also possible to use the word DER to include the raw encoded data in any extension. 1.2.3.4 = critical, DER:01:02:03:04 1.2.3.4.1 = DER:01020304 The value following DER is a hex dump of the DER encoding of the extension Any extension can be placed in this form to override the default behaviour. For example: basicConstraints = critical, DER:00:01:02:03 =head1 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 DER and ASN1 options should be used with caution. It is possible to create invalid extensions if they are not used carefully. =head1 SEE ALSO L, L, L, L =head1 COPYRIGHT Copyright 2004-2023 The OpenSSL Project Authors. All Rights Reserved. Licensed under the Apache License 2.0 (the "License"). You may not use this file except in compliance with the License. You can obtain a copy in the file LICENSE in the source distribution or at L. =cut