.\" $OpenBSD: x509v3.cnf.5,v 1.6 2019/06/06 01:06:59 schwarze Exp $
.\" full merge up to:
.\" OpenSSL man5/x509v3_config a41815f0 Mar 17 18:43:53 2017 -0700
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.\"
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.Dd $Mdocdate: June 6 2019 $
.Dt X509V3.CNF 5
.Os
.Sh NAME
.Nm x509v3.cnf
.Nd X.509 V3 certificate extension configuration format
.Sh DESCRIPTION
Several of the OpenSSL utilities can add extensions to a certificate or
certificate request based on the contents of a configuration file.
The file format is based on the
.Xr openssl.cnf 5
format.
.Pp
Typically the application will contain an option to point to an
extension section.
Each line of the extension section takes the form:
.Pp
.D1 Ar extension_name Ns = Ns Oo Cm critical , Oc Ar extension_options
.Pp
If
.Cm critical
is present, then the extension will be critical.
.Pp
The format of
.Ar extension_options
depends on the value of
.Ar extension_name .
.Pp
There are four main types of extension: string extensions, multi-valued
extensions, raw extensions, and arbitrary extensions.
.Pp
String extensions simply have a string which contains either the value
itself or how it is obtained.
For example:
.Pp
.Dl nsComment="This is a Comment"
.Pp
Multi-valued extensions have a short form and a long form.
The short form is a list of names and values:
.Pp
.Dl basicConstraints=critical,CA:true,pathlen:1
.Pp
The long form allows the values to be placed in a separate section:
.Bd -literal -offset indent
basicConstraints=critical,@bs_section

[bs_section]
CA=true
pathlen=1
.Ed
.Pp
Both forms are equivalent.
.Pp
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.
.Pp
If an extension type is unsupported, then the arbitrary extension
syntax must be used; see the
.Sx ARBITRARY EXTENSIONS
section for more details.
.Sh STANDARD EXTENSIONS
The following sections describe each supported extension in detail.
.Ss Basic constraints
This is a multi-valued extension which indicates whether a certificate
is a CA certificate.
The first (mandatory) name is
.Ic CA
followed by
.Cm TRUE
or
.Cm FALSE .
If
.Ic CA
is
.Cm TRUE ,
then an optional
.Ic pathlen
name followed by a non-negative value can be included.
For example:
.Bd -literal -offset indent
basicConstraints=CA:TRUE
basicConstraints=CA:FALSE
basicConstraints=critical,CA:TRUE, pathlen:0
.Ed
.Pp
A CA certificate must include the
.Ic basicConstraints
value with the
.Ic CA
field set to
.Cm TRUE .
An end user certificate must either set
.Ic CA
to
.Cm FALSE
or exclude the extension entirely.
Some software may require the inclusion of
.Ic basicConstraints
with
.Ic CA
set to
.Cm FALSE
for end entity certificates.
.Pp
The
.Ic 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
.Ic pathlen
of zero it can only be used to sign end user certificates and not
further CAs.
.Ss Key usage
Key usage is a multi-valued extension consisting of a list of names of
the permitted key usages.
.Pp
The supported names are:
.Ic digitalSignature ,
.Ic nonRepudiation ,
.Ic keyEncipherment ,
.Ic dataEncipherment ,
.Ic keyAgreement ,
.Ic keyCertSign ,
.Ic cRLSign ,
.Ic encipherOnly ,
and
.Ic decipherOnly .
Examples:
.Bd -literal -offset indent
keyUsage=digitalSignature, nonRepudiation
keyUsage=critical, keyCertSign
.Ed
.Ss Extended key usage
This extensions consists of a list of usages indicating purposes for
which the certificate public key can be used for.
.Pp
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:
.Bl -column emailProtection
.It Em value Ta Em meaning
.It Ic serverAuth      Ta SSL/TLS web server authentication
.It Ic clientAuth      Ta SSL/TLS web client authentication
.It Ic codeSigning     Ta code signing
.It Ic emailProtection Ta E-mail protection (S/MIME)
.It Ic timeStamping    Ta trusted timestamping
.It Ic OCSPSigning     Ta OCSP signing
.It Ic ipsecIKE        Ta IPsec internet key exchange
.It Ic msCodeInd       Ta Microsoft individual code signing (authenticode)
.It Ic msCodeCom       Ta Microsoft commercial code signing (authenticode)
.It Ic msCTLSign       Ta Microsoft trust list signing
.It Ic msEFS           Ta Microsoft encrypted file system
.El
.Pp
Examples:
.Bd -literal -offset indent
extendedKeyUsage=critical,codeSigning,1.2.3.4
extendedKeyUsage=serverAuth,clientAuth
.Ed
.Ss Subject key identifier
This is really a string extension and can take two possible values.
Either the word
.Cm hash
which will automatically follow the guidelines in RFC 3280
or a hex string giving the extension value to include.
The use of the hex string is strongly discouraged.
Example:
.Pp
.Dl subjectKeyIdentifier=hash
.Ss Authority key identifier
The authority key identifier extension permits two options,
.Cm keyid
and
.Cm issuer :
both can take the optional value
.Cm always .
.Pp
If the
.Cm keyid
option is present, an attempt is made to copy the subject
key identifier from the parent certificate.
If the value
.Cm always
is present, then an error is returned if the option fails.
.Pp
The
.Cm issuer
option copies the issuer and serial number from the issuer certificate.
This will only be done if the
.Cm keyid
option fails or is not included unless the
.Cm always
flag will always include the value.
Example:
.Pp
.Dl authorityKeyIdentifier=keyid,issuer
.Ss Subject alternative name
The subject alternative name extension allows various literal values to
be included in the configuration file.
These include
.Ic email
(an email address),
.Ic URI
(a uniform resource indicator),
.Ic DNS
(a DNS domain name),
.Ic RID
(a registered ID: OBJECT IDENTIFIER),
.Ic IP
(an IP address),
.Ic dirName
(a distinguished name), and
.Ic otherName .
.Pp
The
.Ic email
option can include a special
.Cm copy
value.
This will automatically include any email addresses contained in the
certificate subject name in the extension.
.Pp
The IP address used in the
.Ic IP
options can be in either IPv4 or IPv6 format.
.Pp
The value of
.Ic 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
.Ql +
character.
.Pp
.Ic otherName
can include arbitrary data associated with an OID: the value should
be the OID followed by a semicolon and the content in standard
.Xr ASN1_generate_nconf 3
format.
Examples:
.Bd -literal -offset 2n
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
.Ed
.Ss Issuer alternative name
The issuer alternative name option supports all the literal options of
subject alternative name.
It does not support the
.Ic email : Ns Cm copy
option because that would not make sense.
It does support an additional
.Ic issuer : Ns Cm copy
option that will copy all the subject alternative name values from
the issuer certificate (if possible).
Example:
.Pp
.Dl issuerAltName = issuer:copy
.Ss Authority info access
The authority information access extension gives details about how to
access certain information relating to the CA.
Its syntax is
.Ar accessOID ; location
where
.Ar location
has the same syntax as subject alternative name (except that
.Ic email : Ns Cm copy
is not supported).
.Ar accessOID
can be any valid OID but only certain values are meaningful,
for example
.Cm OCSP
and
.Cm caIssuers .
Example:
.Bd -literal -offset indent
authorityInfoAccess = OCSP;URI:http://ocsp.my.host/
authorityInfoAccess = caIssuers;URI:http://my.ca/ca.html
.Ed
.Ss CRL distribution points
This is a multi-valued extension whose options can be either in
.Ar name : Ns Ar value
pair form using the same form as subject alternative name or a
single value representing a section name containing all the
distribution point fields.
.Pp
For a
.Ar name : Ns Ar 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.
.Pp
In the single option case, the section indicated contains values
for each field.
In this section:
.Pp
If the name is
.Ic fullname ,
the value field should contain the full name of the distribution
point in the same format as subject alternative name.
.Pp
If the name is
.Ic relativename ,
then the value field should contain a section name whose contents
represent a DN fragment to be placed in this field.
.Pp
The name
.Ic CRLIssuer ,
if present, should contain a value for this field in subject
alternative name format.
.Pp
If the name is
.Ic reasons ,
the value field should consist of a comma separated field containing
the reasons.
Valid reasons are:
.Cm keyCompromise ,
.Cm CACompromise ,
.Cm affiliationChanged ,
.Cm superseded ,
.Cm cessationOfOperation ,
.Cm certificateHold ,
.Cm privilegeWithdrawn ,
and
.Cm AACompromise .
.Pp
Simple examples:
.Bd -literal -offset indent
crlDistributionPoints=URI:http://myhost.com/myca.crl
crlDistributionPoints=URI:http://my.com/my.crl,URI:http://oth.com/my.crl
.Ed
.Pp
Full distribution point example:
.Bd -literal -offset indent
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
.Ed
.Ss 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.
.Pp
The names
.Ic reasons
and
.Ic CRLissuer
are not recognized.
.Pp
The name
.Ic onlysomereasons
is accepted, which sets this field.
The value is in the same format as the CRL distribution point
.Ic reasons
field.
.Pp
The names
.Ic onlyuser ,
.Ic onlyCA ,
.Ic onlyAA ,
and
.Ic indirectCRL
are also accepted.
The values should be a boolean values
.Cm ( TRUE
or
.Cm FALSE )
to indicate the value of the corresponding field.
Example:
.Bd -literal -offset indent
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
.Ed
.Ss Certificate policies
This is a raw extension.
All the fields of this extension can be set by using the appropriate
syntax.
.Pp
If you follow the PKIX recommendations and just use one OID, then you
just include the value of that OID.
Multiple OIDs can be set separated by commas, for example:
.Pp
.Dl certificatePolicies= 1.2.4.5, 1.1.3.4
.Pp
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
.Pf @ Ar section
syntax instead of a literal OID value.
.Pp
The section referred to must include the policy OID using the name
.Ic policyIdentifier .
.Ic CPSuri
qualifiers can be included using the syntax:
.Pp
.D1 Ic CPS . Ns Ar nnn Ns = Ns Ar value
.Pp
.Ic userNotice
qualifiers can be set using the syntax:
.Pp
.D1 Ic userNotice . Ns Ar nnn Ns =@ Ns Ar notice
.Pp
The value of the
.Ic userNotice
qualifier is specified in the relevant section.
This section can include
.Ic explicitText ,
.Ic organization ,
and
.Ic noticeNumbers
options.
.Ic explicitText
and
.Ic organization
are text strings,
and
.Ic noticeNumbers
is a comma separated list of numbers.
The
.Ic organization
and
.Ic noticeNumbers
options (if included) must
.Em both
be present.
If you use the
.Ic userNotice
option with IE5 then you need the
.Ic ia5org
option at the top level to modify the encoding: otherwise it will
not be interpreted properly.
Example:
.Bd -literal -offset indent
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
.Ed
.Pp
The
.Ic ia5org
option changes the type of the
.Ic organization
field.
In RFC 2459, it can only be of type
.Vt DisplayText .
In RFC 3280,
.Vt IA5String
is also permissible.
Some software (for example some versions of MSIE) may require
.Ic ia5org .
.Ss Policy constraints
This is a multi-valued extension which consists of the names
.Ic requireExplicitPolicy
or
.Ic inhibitPolicyMapping
and a non-negative integer value.
At least one component must be present.
Example:
.Pp
.Dl policyConstraints = requireExplicitPolicy:3
.Ss Inhibit any policy
This is a string extension whose value must be a non-negative integer.
Example:
.Pp
.Dl inhibitAnyPolicy = 2
.Ss Name constraints
The name constraints extension is a multi-valued extension.
The name should begin with the word
.Cm permitted
or
.Cm excluded ,
followed by a semicolon.
The rest of the name and the value follows the syntax of subjectAltName
except
.Ic email : Ns Cm copy
is not supported and the
.Ic IP
form should consist of an IP addresses and subnet mask separated
by a slash.
Examples:
.Bd -literal -offset indent
nameConstraints=permitted;IP:192.168.0.0/255.255.0.0
nameConstraints=permitted;email:.somedomain.com
nameConstraints=excluded;email:.com
.Ed
.Ss OCSP no check
The OCSP no check extension is a string extension,
but its value is ignored.
Example:
.Pp
.Dl noCheck = ignored
.Ss 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 in the range from 0 to 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.
.Pp
The supported names are:
.Cm status_request
and
.Cm status_request_v2 .
Example:
.Pp
.Dl tlsfeature = status_request
.Sh DEPRECATED EXTENSIONS
The following extensions are non-standard, Netscape specific and largely
obsolete.
Their use in new applications is discouraged.
.Ss Netscape string extensions
Netscape comment
.Ic ( nsComment )
is a string extension containing a comment which will be displayed when
the certificate is viewed in some browsers.
Example:
.Pp
.Dl nsComment = "Some Random Comment"
.Pp
Other supported extensions in this category are:
.Ic nsBaseUrl ,
.Ic nsRevocationUrl ,
.Ic nsCaRevocationUrl ,
.Ic nsRenewalUrl ,
.Ic nsCaPolicyUrl ,
and
.Ic nsSslServerName .
.Ss 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
.Ic basicConstraints ,
.Ic keyUsage ,
and extended key usage extensions are now used instead.
.Pp
Acceptable values for
.Ic nsCertType
are:
.Cm client ,
.Cm server ,
.Cm email ,
.Cm objsign ,
.Cm reserved ,
.Cm sslCA ,
.Cm emailCA ,
.Cm objCA .
.Sh 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.
.Pp
There are two ways to encode arbitrary extensions.
.Pp
The first way is to use the word
.Cm ASN1
followed by the extension content using the same syntax as
.Xr ASN1_generate_nconf 3 .
For example:
.Bd -literal -offset indent
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
.Ed
.Pp
It is also possible to use the word
.Cm DER
to include the raw encoded data in any extension.
.Bd -literal -offset indent
1.2.3.4=critical,DER:01:02:03:04
1.2.3.4=DER:01020304
.Ed
.Pp
The value following
.Cm 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:
.Pp
.Dl basicConstraints=critical,DER:00:01:02:03
.Sh FILES
.Bl -tag -width /etc/ssl/x509v3.cnf -compact
.It Pa /etc/ssl/x509v3.cnf
standard configuration file
.El
.Sh SEE ALSO
.Xr openssl 1 ,
.Xr ASN1_generate_nconf 3 ,
.Xr OPENSSL_config 3 ,
.Xr openssl.cnf 5
.Sh HISTORY
X509v3 extension code was first added to OpenSSL 0.9.2.
.Sh CAVEATS
There is no guarantee that a specific implementation will process a
given extension.
It may therefore sometimes be 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.
.Pp
The
.Cm DER
and
.Cm ASN1
options should be used with caution.
It is possible to create totally invalid extensions if they are not used
carefully.
.Pp
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,
.Pp
.Dl subjectAltName=URI:ldap://somehost.com/CN=foo,OU=bar
.Pp
will produce an error, but the following form is valid:
.Bd -literal -offset indent
subjectAltName=@subject_alt_section

[subject_alt_section]
subjectAltName=URI:ldap://somehost.com/CN=foo,OU=bar
.Ed
.Pp
Due to the behaviour of the OpenSSL CONF library, the same field
name can only occur once in a section.
That means that
.Bd -literal -offset indent
subjectAltName=@alt_section

[alt_section]
email=steve@here
email=steve@there
.Ed
.Pp
will only use the last value.
This can be worked around by using the form:
.Bd -literal -offset indent
[alt_section]
email.1=steve@here
email.2=steve@there
.Ed