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:
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 ``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.
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.
Examples:
keyUsage = digitalSignature, nonRepudiation keyUsage = critical, keyCertSign
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
Otherwise, the value must be a hex string (possibly with ":" separating bytes) to output directly, however, this is strongly discouraged.
Example:
subjectKeyIdentifier = hash
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.
Examples:
authorityKeyIdentifier = keyid, issuer authorityKeyIdentifier = keyid, issuer:always
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
Example:
issuerAltName = issuer:copy
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:
authorityInfoAccess = OCSP;URI:http://ocsp.example.com/,caIssuers;URI:http://myca.example.com/ca.cer authorityInfoAccess = OCSP;URI:http://ocsp.example.com/
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:
Only one of fullname or relativename should be specified.
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:
[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
Example:
[extensions] issuingDistributionPoint = critical, @idp_section [idp_section] fullname = URI:http://example.com/myca.crl indirectCRL = TRUE onlysomereasons = keyCompromise, CACompromise
Policies without qualifiers are specified by giving the OID. Multiple policies are comma-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 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.
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"
Example:
policyConstraints = requireExplicitPolicy:3
Example:
inhibitAnyPolicy = 2
Examples:
nameConstraints = permitted;IP:192.168.0.0/255.255.0.0 nameConstraints = permitted;email:.example.com nameConstraints = excluded;email:.com
Example:
noCheck = ignored
The supported names are: status_request and status_request_v2.
Example:
tlsfeature = status_request
Acceptable values for nsCertType are: client, server, email, objsign, reserved, sslCA, emailCA, objCA.
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
The DER and ASN1 options should be used with caution. It is possible to create invalid extensions if they are not used carefully.
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>.