OpenSL x509v3config(5openssl)
NAME
x509v3config - X509 V3 certificate extension configuration
format
DESCRIPTION
Several of the OpenSL 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:
extensionname=[critical,] extensionoptions
If critical is present then the extension will be critical.
The format of extensionoptions depends on the value of
extensionname.
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,@bssection
[bssection]
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.
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If an extension type is unsupported then the arbitrary
extension syntax must be used, see the ARBITRART 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 supporte names are: digitalSignature, nonRepudiation,
keyEncipherment, dataEncipherment, keyAgreement,
keyCertSign, cRLSign, encipherOnly and decipherOnly.
Examples:
keyUsage=digitalSignature, nonRepudiation
keyUsage=critical, keyCertSign
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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 of 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 SL/TLS Web Server Authentication.
clientAuth SL/TLS Web Client Authentication.
codeSigning Code signing.
emailProtection E-mail Protection (S/MIME).
timeStamping Trusted Timestamping
msCodeInd Microsoft Individual Code Signing (authenticode)
msCodeCom Microsoft Commercial Code Signing (authenticode)
msCTLSign Microsoft Trust List Signing
msSGC Microsoft Server Gated Crypto
msEFS Microsoft Encrypted File System
nsSGC Netscape Server Gated Crypto
Examples:
extendedKeyUsage=critical,codeSigning,1.2.3.4
extendedKeyUsage=nsSGC,msSGC
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.
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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 and 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 preceeding 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 ASN1generatenconf() 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:dirsect
[dirsect]
C=UK
O=My Organization
OU=My Unit
CN=My Name
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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:
issuserAltName = 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 that supports all the
literal options of subject alternative name. Of the few
software packages that currently interpret this extension
most only interpret the URI option.
Currently each option will set a new DistributionPoint with
the fullName field set to the given value.
Other fields like cRLissuer and reasons cannot currently be
set or displayed: at this time no examples were available
that used these fields.
Examples:
crlDistributionPoints=URI:http:/myhost.com/myca.crl
crlDistributionPoints=URI:http:/my.com/my.crl,URI:http:/oth.com/my.crl
Certificate Policies.
This is a raw extension. All the fields of this extension
can be set by using the appropriate syntax.
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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 IA5Strring is also permissible. Some software (for
example some versions of MSIE) may require ia5org.
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Policy Constraints
This is a multi-valued extension which consisting of the
names requireExplicitPolicy or inhibitPolicyMapping and a
non negative intger 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
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"
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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 OpenSL 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
ASN1generatenconf(). For example:
1.2.3.4=critical,ASN1:UTF8String:Some random data
1.2.3.4=ASN1:SEQUENCE:seqsect
[seqsect]
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
WARNING
There is no guarantee that a specific implementation will
process a given extension. It may therefore be sometimes
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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=@subjectaltsection
[subjectaltsection]
subjectAltName=URI:ldap:/somehost.com/CN=foo,OU=bar
is valid.
Due to the behaviour of the OpenSL conf library the same
field name can only occur once in a section. This means
that:
subjectAltName=@altsection
[altsection]
email=steve@here
email=steve@there
will only recognize the last value. This can be worked
around by using the form:
[altsection]
email.1=steve@here
email.2=steve@there
HISTORY
The X509v3 extension code was first added to OpenSL 0.9.2.
Policy mappings, inhibit any policy and name constraints
support was added in OpenSL 0.9.8
The directoryName and otherName option as well as the ASN1
option for arbitrary extensions was added in OpenSL 0.9.8
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SEE ALSO
req(1), ca(1), x509(1)
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