Provided by: openssl_3.0.5-2ubuntu1_amd64 bug


       x509v3_config - X509 V3 certificate extension configuration format


       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 -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:

        name = [critical, ]value(s)

       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:


       Each is described in the following paragraphs.

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

       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:

        basicConstraints = critical, @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://,OU=bar

       will produce an error but the equivalent form:

        subjectAltName = @subject_alt_section

        subjectAltName = URI:ldap://,OU=bar

       is valid.

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

        subjectAltName = @alt_section

        email =
        email =

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

        subjectAltName = @alt_section

        email.1 =
        email.2 =

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

       If an extension type is unsupported, then the arbitrary extension syntax must be used, see
       the "ARBITRARY EXTENSIONS" section for more details.


       The following sections describe the syntax of each supported extension.  They do not
       define the semantics of the extension.

   Basic Constraints
       This is a multi-valued extension which indicates whether a certificate is a CA
       certificate. The first value is CA followed by TRUE or FALSE. If CA is TRUE then an
       optional pathlen 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 must include the basicConstraints name with the CA parameter set to TRUE.
       An end-user certificate must either have CA:FALSE 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 CA cannot sign any sub-CA's, and can only sign end-
       entity certificates.

   Key Usage
       Key usage is a multi-valued extension consisting of a list of names of the permitted key
       usages.  The defined values are: "digitalSignature", "nonRepudiation", "keyEncipherment",
       "dataEncipherment", "keyAgreement", "keyCertSign", "cRLSign", "encipherOnly", and


        keyUsage = digitalSignature, nonRepudiation

        keyUsage = critical, keyCertSign

   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 id-kp-serverAuth and id-kp-clientAuth 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.


        extendedKeyUsage = critical, codeSigning,

        extendedKeyUsage = serverAuth, clientAuth

   Subject Key Identifier
       The SKID extension specification has a value with three choices.  If the value is the word
       none then no SKID extension will be included.  If the value is the word hash, or by
       default for the x509, req, and ca apps, the process specified in RFC 5280 section
       (1) is followed: 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).

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


        subjectKeyIdentifier = hash

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

       If keyid is present, an attempt is made to copy the subject key identifier (SKID) 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 DN and serial number are copied from the issuer certificate.


        authorityKeyIdentifier = keyid, issuer

        authorityKeyIdentifier = keyid, issuer:always

   Subject Alternative Name
       This is a multi-valued extension that supports several types of name identifier, including
       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 syntax of each is described in the following paragraphs.

       The email option has two special values.  "copy" will automatically include any email
       addresses contained in the certificate subject name in the extension.  "move" will
       automatically move any email addresses from the certificate subject name to the extension.

       The IP address used in the IP 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 OID; the value should
       be the OID followed by a semicolon and the content in specified using the syntax in


        subjectAltName = email:copy,, URI:

        subjectAltName = IP:

        subjectAltName = IP:13::17

        subjectAltName =, RID:

        subjectAltName = otherName:;UTF8:some other identifier

        subjectAltName = dirName:dir_sect

        C = UK
        O = My Organization
        OU = My Unit
        CN = My Name

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

        otherName =;FORMAT:UTF8,

   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.


        issuerAltName = issuer:copy

   Authority Info Access
       This extension gives details about how to retrieve information that related to the
       certificate that the CA makes available. The syntax is access_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 OCSP (OCSP responder), caIssuers (CA Issuers),
       ad_timestamping (AD Time Stamping), AD_DVCS (ad dvcs), caRepository (CA Repository).


        authorityInfoAccess = OCSP;URI:,caIssuers;URI:

        authorityInfoAccess = OCSP;URI:

   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:

           The full name of the distribution point, in the same format as the subject alternative

           The value is taken as a distinguished name fragment that is set as the value of the
           nameRelativeToCRLIssuer field.

           The value must in the same format as the subject alternative name.

           A multi-value field that contains the reasons for revocation. The recognized values
           are: "keyCompromise", "CACompromise", "affiliationChanged", "superseded",
           "cessationOfOperation", "certificateHold", "privilegeWithdrawn", and "AACompromise".

       Only one of fullname or relativename should be specified.

       Simple examples:

        crlDistributionPoints = URI:

        crlDistributionPoints = URI:, URI:

       Full distribution point example:

        crlDistributionPoints = crldp1_section

        fullname = URI:
        CRLissuer = dirName:issuer_sect
        reasons = keyCompromise, CACompromise

        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. The
       following names have meaning:

           The full name of the distribution point, in the same format as the subject alternative

           The value is taken as a distinguished name fragment that is set as the value of the
           nameRelativeToCRLIssuer field.

           A multi-value field that contains the reasons for revocation. The recognized values
           are: "keyCompromise", "CACompromise", "affiliationChanged", "superseded",
           "cessationOfOperation", "certificateHold", "privilegeWithdrawn", and "AACompromise".

       onlyuser, onlyCA, onlyAA, indirectCRL
           The value for each of these names is a boolean.


        issuingDistributionPoint = critical, @idp_section

        fullname = URI:
        indirectCRL = TRUE
        onlysomereasons = keyCompromise, CACompromise

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

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

        certificatePolicies =,

       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 policyIdentifier.
       cPSuri qualifiers can be included using the syntax:

        CPS.nnn = value

       where "nnn" 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 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 BOTH be present. Some software
       might require the ia5org option at the top level; this changes the encoding from
       Displaytext to IA5String.


        certificatePolicies = ia5org,,, @polsect

        policyIdentifier =
        CPS.1 = ""
        CPS.2 = ""
        userNotice.1 = @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 UTF8,
       BMP, or VISIBLE followed by colon. For example:

        explicitText = "UTF8:Explicit Text Here"

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


        policyConstraints = requireExplicitPolicy:3

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


        inhibitAnyPolicy = 2

   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 email:copy is not supported and the IP form should consist of an IP
       addresses and subnet mask separated by a /.


        nameConstraints = permitted;IP:

        nameConstraints = permitted;

        nameConstraints = excluded;

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


        noCheck = ignored

   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: status_request and status_request_v2.


        tlsfeature = status_request


       The following extensions are non standard, Netscape specific and largely obsolete. Their
       use in new applications is discouraged.

   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, nsRevocationUrl, nsCaRevocationUrl, nsRenewalUrl, nsCaPolicyUrl and

   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.


       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 ASN1_generate_nconf(3).  For example:

        [extensions] = critical, ASN1:UTF8String:Some random data = ASN1:SEQUENCE: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. = critical, DER:01:02:03:04 = 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


       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.


       openssl-req(1), openssl-ca(1), openssl-x509(1), ASN1_generate_nconf(3)


       Copyright 2004-2021 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 <>.