X509V3_CONFIG(5SSL)

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version 4.0.3 · 13 versions
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✨ NAME ✨

x509v3_config — X509 V3 certificate extension configuration format

🌸 DESCRIPTION 🌸

Okay bestie, so like 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 it needs one 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. periodt.

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:

  • 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. slay.

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 "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.

👑 STANDARD EXTENSIONS 👑

The following sections describe the syntax of each supported extension. They do not define the semantics of the extension. syntax only, no cap.

🔑 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 (with an alternative name contentCommitment), keyEncipherment, dataEncipherment, keyAgreement, keyCertSign, cRLSign, encipherOnly, and decipherOnly.

Examples:

keyUsage = digitalSignature, nonRepudiation

keyUsage = digitalSignature, contentCommitment

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 (columns: 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.

Examples:

extendedKeyUsage = critical, codeSigning, 1.2.3.4

extendedKeyUsage = serverAuth, clientAuth

🪪 Subject Key Identifier

The Subject Key Identifier (SKID) extension takes three possible forms:

  • none — No SKID extension will be included.
  • hash — The process specified in RFC 5280 section 4.2.1.2. (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).
  • A hex string (possibly with ":" separating bytes) — The specified value is used directly. This choice is strongly discouraged. like, don't.

See openssl-x509(1), openssl-req(1), and openssl-ca(1) documentation for further details relevant to each of the command-line utilities.

Example:

subjectKeyIdentifier = hash

🗝️ Authority Key Identifier

The Authority Key Identifier (SKID) extension takes two different forms.

The value none indicates that no AKID shall be included.

Otherwise, the value syntax is that of a comma-separated list of either or both of the keyid or issuer keywords.

The keyid keyword asks that the AKID include the issuer's subject key identifier.

The issuer keyword asks that the AKID include the serial number and issuer distinguished name (grandparent name of subject certificate) of the issuer certificate. Unless qualified with "always" (as described below), these are added only as a fallback if the keyid is not requested, or no SKID was available in the issuer certificate.

Either or both keywords can be suffixed with an optional qualifier, which can be either "always" or "nonss". If the qualifier is present, it is separated from the keyword by a colon (":").

The "always" qualifier makes that AKID element mandatory, an error is raised if that element cannot be included. The issuer certificate's issuer name and serial number are no longer a fallback when the always qualifier is used. The "nonss" qualifier makes that AKID element further conditional on the certificate not being self-signed.

When creating a self-signed certificate, be sure to specify a SKID extension if you want to have a mandatory ("always" qualified) keyid in the AKID extension.

See openssl-x509(1), openssl-req(1), and openssl-ca(1) for further details relevant to that specific command-line utility.

Examples:

# Keyid preferred, otherwise issuer name & serial
authorityKeyIdentifier = keyid, issuer

# As above, but skip the extension entirely if self-signed
authorityKeyIdentifier = keyid:nonss, issuer:nonss

# Keyid when possible, issuer name & serial always
authorityKeyIdentifier = keyid, issuer:always

# Keyid when possible, issuer as fallback when not self-signed
authorityKeyIdentifier = keyid, issuer:nonss

🌐 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 ASN1_generate_nconf(3).

Examples:

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

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

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

🏷️ 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:

issuerAltName = issuer:copy

🌈 Authority Info Access 🌈

okay so this extension is literally the "how do I find out more about this cert" card 💳 It hands over the deets on how to retrieve info that's related to the certificate that the CA makes available.

The syntax is access_id;location, where access_id is an object identifier (even tho only a few values are well-known, sad) and location has the exact same syntax as subject alternative name — except that email:copy is just not supported, bestie, don't try it 🙅‍♀️

Possible values for access_id include:

  • OCSP — OCSP responder
  • caIssuers — CA Issuers
  • ad_timestamping — AD Time Stamping
  • AD_DVCS — ad dvcs
  • caRepository — CA Repository

Examples, periodt:

authorityInfoAccess = OCSP;URI:http://ocsp.example.com/,caIssuers;URI:http://myca.example.com/ca.cer

authorityInfoAccess = OCSP;URI:http://ocsp.example.com/

📍 CRL distribution points 📍

This one's multi-valued, and its values can go two ways: either a name-value pair using the same form as subject alternative name, or a single value that names the section holding all the distribution point values. Pick your fighter 💅

When a name-value pair is used, a DistributionPoint extension gets set with the given value as the fullName field as the distributionPoint value, and the reasons and cRLIssuer fields will be omitted (they simply didn't show up to the party 🫥).

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

  • fullname — the full name of the distribution point, in the same format as the subject alternative name.
  • relativename — the value is taken as a distinguished name fragment that is set as the value of the nameRelativeToCRLIssuer field.
  • CRLIssuer — the value must in the same format as the subject alternative name.
  • reasons — 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 — not both, that's not the vibe 🚫

Simple examples:

crlDistributionPoints = URI:http://example.com/myca.crl

crlDistributionPoints = URI:http://example.com/myca.crl, URI:http://example.org/my.crl

Full distribution point example (the whole glow-up ✨):

[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

👑 Issuing Distribution Point 👑

This extension should only appear in CRLs, no cap. It's multi-valued and its syntax is similar to the "section" pointed to by the CRL distribution points extension. The following names have meaning:

  • fullname — the full name of the distribution point, in the same format as the subject alternative name.
  • relativename — the value is taken as a distinguished name fragment that is set as the value of the nameRelativeToCRLIssuer field.
  • onlysomereasons — 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.

Example:

[extensions]
issuingDistributionPoint = critical, @idp_section

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

🎀 Certificate Policies 🎀

This is a raw extension that supports all of the defined fields of the certificate extension. Versatile much? 💖

Policies without qualifiers are specified by giving the OID. Multiple policies are comma-separated — slay. 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 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 — they're a package deal, iykyk 🫶 Some software might require the ia5org 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 UTF8, BMP, or VISIBLE followed by colon. For example:

[notice]
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 present — no empty sections allowed bestie 💀

Example:

policyConstraints = requireExplicitPolicy:3

🍓 Inhibit Any Policy 🍓

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

Example:

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 (again! the disrespect 😭) and the IP form should consist of an IP addresses and subnet mask separated by a /.

Examples:

nameConstraints = permitted;IP:192.168.0.0/255.255.0.0

nameConstraints = permitted;email:.example.com

nameConstraints = excluded;email:.com

💜 OCSP No Check 💜

This is a string extension. It is parsed, but ignored. It's giving "I'm here but I'm not participating" 🙈

Example:

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 — reciprocation, we love to see it ✨

The supported names are: status_request and status_request_v2.

Example:

tlsfeature = status_request

💀 DEPRECATED EXTENSIONS 💀

The following extensions are non standard, Netscape specific and largely obsolete. Their use in new applications is discouraged. Like, truly, don't. This is vintage in the bad way 🙅‍♀️

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 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. We moved on, babe 💅

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

🦋 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. This is not a drill bestie, one wrong byte and it's over 😭

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]
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

⚠️ 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. Yeah. The rules only apply if everyone's playing the same game 🫠

The DER and ASN1 options should be used with caution. It is possible to create invalid extensions if they are not used carefully. Be careful, be cunty, but be careful 💅

👀 SEE ALSO 👀

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

📜 HISTORY 📜

OpenSSL 4.0 updated the syntax of the subjectKeyIdentifier (SKID) and authorityKeyIdentifier (AKID) extensions, described above, to introduce the "nonss" qualifier for the keyid and issuer keywords. The command-line utilities no longer have specialised built-in logic to add these extensions, they are handled through configuration files and command-line options just like any other extension. Glow-up era for real 🔥

Copyright 2004-2026 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 <https://www.openssl.org/source/license.html>.

and that's the whole page bestie, we ate and left no crumbs 👑 This was X509V3_CONFIG(5SSL) from OpenSSL 4.0.3, dated 2026-09-29 — go forth and configure those extensions correctly, I'm obsessed with you 🫶💖✨

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