Provided by: openssl_1.1.1f-1ubuntu2.23_amd64 
NAME
x509v3_config - X509 V3 certificate extension configuration format
DESCRIPTION
Several of the OpenSSL utilities can add extensions to a certificate or certificate
request based on the contents of a configuration file.
Typically the application will contain an option to point to an extension section. Each
line of the extension section takes the form:
extension_name=[critical,] extension_options
If critical is present then the extension will be critical.
The format of extension_options depends on the value of extension_name.
There are four main types of extension: string extensions, multi-valued extensions, raw
and arbitrary extensions.
String extensions simply have a string which contains either the value itself or how it is
obtained.
For example:
nsComment="This is a Comment"
Multi-valued extensions have a short form and a long form. The short form is a 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,@bs_section
[bs_section]
CA=true
pathlen=1
Both forms are equivalent.
The syntax of raw extensions is governed by the extension code: it can for example contain
data in multiple sections. The correct syntax to use is defined by the extension code
itself: check out the certificate policies extension for an example.
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 each supported extension in detail.
Basic Constraints.
This is a multi valued extension which indicates whether a certificate is a CA
certificate. The first (mandatory) name is CA followed by TRUE or FALSE. If CA is TRUE
then an optional pathlen name followed by an non-negative value can be included.
For example:
basicConstraints=CA:TRUE
basicConstraints=CA:FALSE
basicConstraints=critical,CA:TRUE, pathlen:0
A CA certificate must include the basicConstraints value with the CA field set to TRUE. An
end user certificate must either set CA to FALSE or exclude the extension entirely. Some
software may require the inclusion of basicConstraints with CA set to FALSE for end entity
certificates.
The pathlen parameter indicates the maximum number of CAs that can appear below this one
in a chain. So if you have a CA with a pathlen of zero it can only be used to sign end
user certificates and not further CAs.
Key Usage.
Key usage is a multi valued extension consisting of a list of names of the permitted key
usages.
The supported names are: digitalSignature, nonRepudiation, keyEncipherment,
dataEncipherment, keyAgreement, keyCertSign, cRLSign, encipherOnly and decipherOnly.
Examples:
keyUsage=digitalSignature, nonRepudiation
keyUsage=critical, keyCertSign
Extended Key Usage.
This extensions consists of a list of usages indicating purposes for which the certificate
public key can be used for,
These can either be object short names or the dotted numerical form of OIDs. While any
OID can be used only certain values make sense. In particular the following PKIX, NS and
MS values are meaningful:
Value Meaning
----- -------
serverAuth SSL/TLS Web Server Authentication.
clientAuth SSL/TLS Web 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
Examples:
extendedKeyUsage=critical,codeSigning,1.2.3.4
extendedKeyUsage=serverAuth,clientAuth
Subject Key Identifier.
This is really a string extension and can take two possible values. Either the word hash
which will automatically follow the guidelines in RFC3280 or a hex string giving the
extension value to include. The use of the hex string is strongly discouraged.
Example:
subjectKeyIdentifier=hash
Authority Key Identifier.
The authority key identifier extension permits two options. keyid and issuer: both can
take the optional value "always".
If the keyid option is present an attempt is made to copy the subject key identifier from
the parent certificate. If the value "always" is present then an error is returned if the
option fails.
The issuer option copies the issuer and serial number from the issuer certificate. This
will only be done if the keyid option fails or is not included unless the "always" flag
will always include the value.
Example:
authorityKeyIdentifier=keyid,issuer
Subject Alternative Name.
The subject alternative name extension allows various literal values to be included in the
configuration file. These include 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 email option include a special 'copy' value. This will automatically include any email
addresses contained in the certificate subject name in the extension.
The IP address used in the IP options can be in either IPv4 or IPv6 format.
The value of dirName should point to a section containing the distinguished name to use as
a set of name value pairs. Multi values AVAs can be formed by prefacing the name with a +
character.
otherName can include arbitrary data associated with an OID: the value should be the OID
followed by a semicolon and the content in standard ASN1_generate_nconf(3) format.
Examples:
subjectAltName=email:copy,email:my@other.address,URI:http://my.url.here/
subjectAltName=IP:192.168.7.1
subjectAltName=IP:13::17
subjectAltName=email:my@other.address,RID:1.2.3.4
subjectAltName=otherName:1.2.3.4;UTF8:some other identifier
subjectAltName=dirName:dir_sect
[dir_sect]
C=UK
O=My Organization
OU=My Unit
CN=My Name
Issuer Alternative Name.
The issuer alternative name option supports all the literal options of subject alternative
name. It does not support the email:copy option because that would not make sense. It does
support an additional issuer:copy option that will copy all the subject alternative name
values from the issuer certificate (if possible).
Example:
issuerAltName = issuer:copy
Authority Info Access.
The authority information access extension gives details about how to access certain
information relating to the CA. Its syntax is accessOID;location where location has the
same syntax as subject alternative name (except that email:copy is not supported).
accessOID can be any valid OID but only certain values are meaningful, for example OCSP
and caIssuers.
Example:
authorityInfoAccess = OCSP;URI:http://ocsp.my.host/
authorityInfoAccess = caIssuers;URI:http://my.ca/ca.html
CRL distribution points
This is a multi-valued extension whose options can be either in name:value pair using the
same form as subject alternative name or a single value representing a section name
containing all the distribution point fields.
For a name:value pair a new DistributionPoint with the fullName field set to the given
value both the cRLissuer and reasons fields are omitted in this case.
In the single option case the section indicated contains values for each field. In this
section:
If the name is "fullname" the value field should contain the full name of the distribution
point in the same format as subject alternative name.
If the name is "relativename" then the value field should contain a section name whose
contents represent a DN fragment to be placed in this field.
The name "CRLIssuer" if present should contain a value for this field in subject
alternative name format.
If the name is "reasons" the value field should consist of a comma separated field
containing the reasons. Valid reasons are: "keyCompromise", "CACompromise",
"affiliationChanged", "superseded", "cessationOfOperation", "certificateHold",
"privilegeWithdrawn" and "AACompromise".
Simple examples:
crlDistributionPoints=URI:http://myhost.com/myca.crl
crlDistributionPoints=URI:http://my.com/my.crl,URI:http://oth.com/my.crl
Full distribution point example:
crlDistributionPoints=crldp1_section
[crldp1_section]
fullname=URI:http://myhost.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. It is a multi valued extension whose syntax is
similar to the "section" pointed to by the CRL distribution points extension with a few
differences.
The names "reasons" and "CRLissuer" are not recognized.
The name "onlysomereasons" is accepted which sets this field. The value is in the same
format as the CRL distribution point "reasons" field.
The names "onlyuser", "onlyCA", "onlyAA" and "indirectCRL" are also accepted the values
should be a boolean value (TRUE or FALSE) to indicate the value of the corresponding
field.
Example:
issuingDistributionPoint=critical, @idp_section
[idp_section]
fullname=URI:http://myhost.com/myca.crl
indirectCRL=TRUE
onlysomereasons=keyCompromise, CACompromise
[issuer_sect]
C=UK
O=Organisation
CN=Some Name
Certificate Policies.
This is a raw extension. All the fields of this extension can be set by using the
appropriate syntax.
If you follow the PKIX recommendations and just using one OID then you just include the
value of that OID. Multiple OIDs can be set separated by commas, for example:
certificatePolicies= 1.2.4.5, 1.1.3.4
If you wish to include qualifiers then the policy OID and qualifiers need to be specified
in a separate section: this is done by using the @section syntax instead of a literal OID
value.
The section referred to must include the policy OID using the name policyIdentifier,
cPSuri qualifiers can be included using the syntax:
CPS.nnn=value
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. If you use the
userNotice option with IE5 then you need the 'ia5org' option at the top level to modify
the encoding: otherwise it will not be interpreted properly.
Example:
certificatePolicies=ia5org,1.2.3.4,1.5.6.7.8,@polsect
[polsect]
policyIdentifier = 1.3.5.8
CPS.1="http://my.host.name/"
CPS.2="http://my.your.name/"
userNotice.1=@notice
[notice]
explicitText="Explicit Text Here"
organization="Organisation Name"
noticeNumbers=1,2,3,4
The ia5org option changes the type of the organization field. In RFC2459 it can only be of
type DisplayText. In RFC3280 IA5String is also permissible. Some software (for example
some versions of MSIE) may require ia5org.
ASN1 type of explicitText can be specified by prepending UTF8, BMP or VISIBLE prefix
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.
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
The name constraints extension 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 /.
Examples:
nameConstraints=permitted;IP:192.168.0.0/255.255.0.0
nameConstraints=permitted;email:.somedomain.com
nameConstraints=excluded;email:.com
OCSP No Check
The OCSP No Check extension is a string extension but its value is ignored.
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.
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.
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.
Example:
nsComment = "Some Random Comment"
Other supported extensions in this category 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.
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.
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:
1.2.3.4=critical,ASN1:UTF8String:Some random data
1.2.3.4=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=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.
The DER and ASN1 options should be used with caution. It is possible to create totally
invalid extensions if they are not used carefully.
NOTES
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:
subjectAltName=@subject_alt_section
[subject_alt_section]
subjectAltName=URI:ldap://somehost.com/CN=foo,OU=bar
is valid.
Due to the behaviour of the OpenSSL conf library the same field name can only occur once
in a section. This means that:
subjectAltName=@alt_section
[alt_section]
email=steve@here
email=steve@there
will only recognize the last value. This can be worked around by using the form:
[alt_section]
email.1=steve@here
email.2=steve@there
SEE ALSO
req(1), ca(1), x509(1), ASN1_generate_nconf(3)
COPYRIGHT
Copyright 2004-2019 The OpenSSL Project Authors. All Rights Reserved.
Licensed under the OpenSSL license (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>.