libcrypto/man/openssl.cnf.5

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.Dd $Mdocdate: July 8 2024 $
.Dt OPENSSL.CNF 5
.Os
.Sh NAME
.Nm openssl.cnf
.Nd OpenSSL configuration files
.Sh DESCRIPTION
The OpenSSL CONF library can be used to read configuration files; see
.Xr CONF_modules_load_file 3 .
It is used for the OpenSSL master configuration file
.Pa /etc/ssl/openssl.cnf
and in a few other places such as certificate extension files for the
.Xr openssl 1
.Cm x509
utility.
OpenSSL applications can also use the CONF library for their own
purposes.
.Pp
A configuration file is divided into a number of sections.
Each section starts with a line
.Bq Ar section_name
and ends when a new section is started or the end of the file is reached.
A section name can consist of alphanumeric characters and underscores.
.Pp
The first section of a configuration file is special and is referred to
as the
.Dq default section .
It is usually unnamed and extends from the start of file to the
first named section.
When a name is being looked up, it is first looked up in a named
section (if any) and then in the default section.
.Pp
The environment is mapped onto a section called
.Ic ENV .
.Pp
Comments can be included by preceding them with the
.Ql #
character.
.Pp
Each section in a configuration file consists of a number of name and
value pairs of the form
.Ar name Ns = Ns Ar value .
.Pp
The
.Ar name
string can contain any alphanumeric characters as well as a few
punctuation symbols such as
.Ql \&.
.Ql \&,
.Ql \&;
and
.Ql _ .
.Pp
The
.Ar value
string consists of the string following the
.Ql =
character until the end of the line with any leading and trailing
whitespace removed.
.Pp
The value string undergoes variable expansion.
This can be done by including substrings of the form
.Pf $ Ar name
or
.Pf $ Brq Ar name :
this will substitute the value of the named variable in the current
section.
It is also possible to substitute a value from another section using the
syntax
.Pf $ Ar section Ns :: Ns Ar name
or
.Pf $ Brq Ar section Ns :: Ns Ar name .
By using the form
.Pf $ Ic ENV Ns :: Ns Ar name ,
environment variables can be substituted.
It is also possible to assign values to environment variables by using
the name
.Ic ENV Ns :: Ns Ar name .
This will work if the program looks up environment variables using
the CONF library instead of calling
.Xr getenv 3
directly.
The value string must not exceed 64k in length after variable expansion or an
error will occur.
.Pp
It is possible to escape certain characters by using any kind of quote
or the
.Ql \e
character.
By making the last character of a line a
.Ql \e ,
a
.Ar value
string can be spread across multiple lines.
In addition the sequences
.Ql \en ,
.Ql \er ,
.Ql \eb ,
and
.Ql \et
are recognized.
.Sh OPENSSL LIBRARY CONFIGURATION
Applications can automatically configure certain aspects of OpenSSL
using the master OpenSSL configuration file, or optionally an
alternative configuration file.
The
.Xr openssl 1
utility includes this functionality: any sub command uses the master
OpenSSL configuration file unless an option is used in the sub command
to use an alternative configuration file.
.Pp
To enable library configuration, the default section needs to contain
an appropriate line which points to the main configuration section.
The default name is
.Ic openssl_conf ,
which is used by the
.Xr openssl 1
utility.
Other applications may use an alternative name such as
.Sy myapplication_conf .
All library configuration lines appear in the default section
at the start of the configuration file.
.Pp
The configuration section should consist of a set of name value pairs
which contain specific module configuration information.
The
.Ar name
represents the name of the configuration module.
The meaning of the
.Ar value
is module specific: it may, for example, represent a further
configuration section containing configuration module specific
information.
For example:
.Bd -literal -offset indent
# The following line must be in the default section.
openssl_conf = openssl_init

[openssl_init]
oid_section = new_oids

[new_oids]
\&... new oids here ...
.Ed
.Pp
The features of each configuration module are described below.
.Ss ASN1 Object Configuration Module
This module has the name
.Ic oid_section .
The value of this variable points to a section containing name value
pairs of OIDs: the name is the OID short and long name, and the value is the
numerical form of the OID.
Although some of the
.Xr openssl 1
utility subcommands already have their own ASN1 OBJECT section
functionality, not all do.
By using the ASN1 OBJECT configuration module, all the
.Xr openssl 1
utility subcommands can see the new objects as well as any compliant
applications.
For example:
.Bd -literal -offset indent
[new_oids]
some_new_oid = 1.2.3.4
some_other_oid = 1.2.3.5
.Ed
.Pp
It is also possible to set the value to the long name followed by a
comma and the numerical OID form.
For example:
.Pp
.Dl shortName = some object long name, 1.2.3.4
.Sh FILES
.Bl -tag -width /etc/ssl/openssl.cnf -compact
.It Pa /etc/ssl/openssl.cnf
standard configuration file
.El
.Sh EXAMPLES
Here is a sample configuration file using some of the features
mentioned above:
.Bd -literal -offset indent
# This is the default section.
HOME=/temp
RANDFILE= ${ENV::HOME}/.rnd
configdir=$ENV::HOME/config

[ section_one ]
# We are now in section one.

# Quotes permit leading and trailing whitespace
any = " any variable name "

other = A string that can \e
cover several lines \e
by including \e\e characters

message = Hello World\en

[ section_two ]
greeting = $section_one::message
.Ed
.Pp
This next example shows how to expand environment variables safely.
.Pp
Suppose you want a variable called
.Sy tmpfile
to refer to a temporary filename.
The directory it is placed in can determined by the
.Ev TEMP
or
.Ev TMP
environment variables but they may not be set to any value at all.
If you just include the environment variable names and the variable
doesn't exist then this will cause an error when an attempt is made to
load the configuration file.
By making use of the default section both values can be looked up with
.Ev TEMP
taking priority and
.Pa /tmp
used if neither is defined:
.Bd -literal -offset indent
TMP=/tmp
# The above value is used if TMP isn't in the environment
TEMP=$ENV::TMP
# The above value is used if TEMP isn't in the environment
tmpfile=${ENV::TEMP}/tmp.filename
.Ed
.Pp
More complex OpenSSL library configuration.
Add OID:
.Bd -literal -offset indent
# Default appname: should match "appname" parameter (if any)
# supplied to CONF_modules_load_file et al.
openssl_conf = openssl_conf_section

[openssl_conf_section]
# Configuration module list
oid_section = new_oids

[new_oids]
# New OID, just short name
newoid1 = 1.2.3.4.1
# New OID shortname and long name
newoid2 = New OID 2 long name, 1.2.3.4.2
.Ed
.Pp
The above examples can be used with any application supporting library
configuration if "openssl_conf" is modified to match the appropriate
"appname".
.Pp
For example if the second sample file above is saved to "example.cnf"
then the command line:
.Pp
.Dl OPENSSL_CONF=example.cnf openssl asn1parse -genstr OID:1.2.3.4.1
.Pp
will output:
.Dl 0:d=0  hl=2 l=   4 prim: OBJECT            :newoid1
.Pp
showing that the OID "newoid1" has been added as "1.2.3.4.1".
.Sh SEE ALSO
.Xr openssl 1 ,
.Xr CONF_modules_load_file 3 ,
.Xr OPENSSL_config 3 ,
.Xr x509v3.cnf 5
.Sh CAVEATS
If a configuration file attempts to expand a variable that doesn't
exist, then an error is flagged and the file will not load.
This can also happen if an attempt is made to expand an environment
variable that doesn't exist.
For example, in a previous version of OpenSSL the default OpenSSL
master configuration file used the value of
.Ev HOME
which may not be defined on non Unix systems and would cause an error.
.Pp
This can be worked around by including a default section to provide
a default value: then if the environment lookup fails, the default
value will be used instead.
For this to work properly, the default value must be defined earlier
in the configuration file than the expansion.
See the
.Sx EXAMPLES
section for an example of how to do this.
.Pp
If the same variable is defined more than once in the same section,
then all but the last value will be silently ignored.
In certain circumstances such as with DNs, the same field may occur
multiple times.
This is usually worked around by ignoring any characters before an
initial
.Ql \&. ,
for example:
.Bd -literal -offset indent
1.OU="My first OU"
2.OU="My Second OU"
.Ed
.Sh BUGS
Currently there is no way to include characters using the octal
.Pf \e Ar nnn
form.
Strings are all NUL terminated, so NUL bytes cannot form part of
the value.
.Pp
The escaping isn't quite right: if you want to use sequences like
.Ql \en ,
you can't use any quote escaping on the same line.
.Pp
Files are loaded in a single pass.
This means that a variable expansion will only work if the variables
referenced are defined earlier in the file.