=pod

=head1 NAME

config - OpenSSL CONF library configuration files

=head1 DESCRIPTION

This page documents the syntax of OpenSSL configuration files,
as parsed by L<NCONF_load(3)> and related functions.
This format is used by many of the OpenSSL commands, and to
initialize the libraries when used by any application.

The first part describes the general syntax of the configuration
files, and subsequent sections describe the semantics of individual
modules. Other modules are described in L<fips_config(5)> and
L<x509v3_config(5)>.
The syntax for defining ASN.1 values is described in
L<ASN1_generate_nconf(3)>.

=head1 SYNTAX

A configuration file is a series of lines.  Blank lines, and whitespace
between the elements of a line, have no significance. A comment starts
with a B<#> character; the rest of the line is ignored. If the B<#>
is the first non-space character in a line, the entire line is ignored.

=head2 Directives

Two directives can be used to control the parsing of configuration files:
B<.include> and B<.pragma>.

For compatibility with older versions of OpenSSL, an equal sign after the
directive will be ignored.  Older versions will treat it as an assignment,
so care should be taken if the difference in semantics is important.

A file can include other files using the include syntax:

  .include [=] pathname

If B<pathname> is a simple filename, that file is included directly at
that point.  Included files can have B<.include> statements that specify
other files.  If B<pathname> is a directory, all files within that directory
that have a C<.cnf> or C<.conf> extension will be included.  (This is only
available on systems with POSIX IO support.)  Any sub-directories found
inside the B<pathname> are B<ignored>.  Similarly, if a file is opened
while scanning a directory, and that file has an B<.include> directive
that specifies a directory, that is also ignored.

As a general rule, the B<pathname> should be an absolute path; this can
be enforced with the B<abspath> and B<includedir> pragmas, described below.
The environment variable B<OPENSSL_CONF_INCLUDE>, if it exists,
is prepended to all relative pathnames.
If the pathname is still relative, it is interpreted based on the
current working directory.

To require all file inclusions to name absolute paths, use the following
directive:

 .pragma [=] abspath:value

The default behavior, where the B<value> is B<false> or B<off>, is to allow
relative paths. To require all B<.include> pathnames to be absolute paths,
use a B<value> of B<true> or B<on>.

In these files, the dollar sign, B<$>, is used to reference a variable, as
described below.  On some platforms, however, it is common to treat B<$>
as a regular character in symbol names.  Supporting this behavior can be
done with the following directive:

 .pragma [=] dollarid:value

The default behavior, where the B<value> is B<false> or B<off>, is to treat
the dollarsign as indicating a variable name; C<foo$bar> is interpreted as
C<foo> followed by the expansion of the variable C<bar>. If B<value> is
B<true> or B<on>, then C<foo$bar> is a single seven-character name and
variable expansions must be specified using braces or parentheses.

 .pragma [=] includedir:value

If a relative pathname is specified in the B<.include> directive, and
the B<OPENSSL_CONF_INCLUDE> environment variable doesn't exist, then
the value of the B<includedir> pragma, if it exists, is prepended to the
pathname.

=head2 Settings

A configuration file is divided into a number of I<sections>.  A section
begins with the section name in square brackets, and ends when a new
section starts, or at the end of the file.  The section name can consist
of alphanumeric characters and underscores.
Whitespace between the name and the brackets is ignored.

The content at the start of the configuration file that precedes its first
named section is special and is referred to as the B<default> or B<unnamed>
section.

The environment is mapped onto a section called B<ENV>.

Within a section are a series of name/value assignments, described in more
detail below.  As a reminder, the square brackets shown in this example
are required, not optional:

 [ section ]
 name1 = This is value1
 name2 = Another value
 ...
 [ newsection ]
 name1 = New value1
 name3 = Value 3

The B<name> can contain any alphanumeric characters as well as a few
punctuation symbols such as B<.> B<,> B<;> and B<_>.
Whitespace after the name and before the equal sign is ignored.

If a name is repeated in the same section, then all but the last
value are ignored. In certain circumstances, such as with
Certificate DNs, the same field may occur multiple times.
In order to support this, commands like L<openssl-req(1)> ignore any
leading text that is preceded with a period. For example:

 1.OU = First OU
 2.OU = Second OU

The B<value> consists of the string following the B<=> character until end
of line with any leading and trailing whitespace removed.

The value string undergoes variable expansion. The text C<$var> or C<${var}>
inserts the value of the named variable from the current section.
To use a value from another section use C<$section::name>
or C<${section::name}>.
By using C<$ENV::name>, the value of the specified environment
variable will be substituted.

Variables must be defined before their value is referenced, otherwise
an error is flagged and the file will not load.
This can be worked around by specifying a default value in the B<default>
section before the variable is used.

Any name/value settings in an B<ENV> section are available
to the configuration file, but are not propagated to the environment.

It is an error if the value ends up longer than 64k.

It is possible to escape certain characters by using a single B<'> or
double B<"> quote around the value, or using a backslash B<\> before the
character,
By making the last character of a line a B<\>
a B<value> string can be spread across multiple lines. In addition
the sequences B<\n>, B<\r>, B<\b> and B<\t> are recognized.

The expansion and escape rules as described above that apply to B<value>
also apply to the pathname of the B<.include> directive.

=head1 OPENSSL LIBRARY CONFIGURATION

The sections below use the informal term I<module> to refer to a part
of the OpenSSL functionality. This is not the same as the formal term
I<FIPS module>, for example.

The OpenSSL configuration looks up the value of B<openssl_conf>
in the default section and takes that as the name of a section that specifies
how to configure any modules in the library.
It is not an error to leave any module in its default configuration.
An application can specify a name other than B<openssl_conf> by, for example,
directly calling L<CONF_modules_load_file(3)>.
The same can also be achieved by calling L<OPENSSL_INIT_set_config_appname(3)>
to set a nondefault application name for use with L<OPENSSL_init_crypto(3)> or
L<OPENSSL_init_ssl(3)>, sufficiently early in the main program, before implicit
OpenSSL library initialisation has taken place as a side-effect of other
OpenSSL function calls.

OpenSSL also looks up the value of the default section's B<config_diagnostics>
parameter.
If this exists and has a nonzero numeric value, any error suppressing flags
passed to CONF_modules_load() will be ignored.
This is useful for diagnosing misconfigurations but its use in
production requires additional consideration.  With this option enabled,
a configuration error will completely prevent access to a service.
Without this option and in the presence of a configuration error, access
will be allowed but the desired configuration will B<not> be used.

 # These must be in the default section
 config_diagnostics = 1
 openssl_conf = openssl_init

 [openssl_init]
 oid_section = oids
 providers = providers
 alg_section = evp_properties
 ssl_conf = ssl_configuration
 random = random

 [oids]
 ... new oids here ...

 [providers]
 ... provider stuff here ...

 [evp_properties]
 ... EVP properties here ...

 [ssl_configuration]
 ... SSL/TLS configuration properties here ...

 [random]
 ... random properties here ...

The semantics of each module are described below. The phrase "in the
initialization section" refers to the section identified by the
B<openssl_conf> or other name (given as B<openssl_init> in the
example above).  The examples below assume the configuration above
is used to specify the individual sections.

=head2 ASN.1 Object Identifier Configuration

The name B<oid_section> in the initialization section names the section
containing name/value pairs of OID's.
The name is the short name; the value is an optional long name followed
by a comma, and the numeric value.
While some OpenSSL commands have their own section for specifying OID's,
this section makes them available to all commands and applications.

 [oids]
 shortName = a very long OID name, 1.2.3.4
 newoid1 = 1.2.3.4.1
 some_other_oid = 1.2.3.5

If a full configuration with the above fragment is in the file
F<example.cnf>, then the following command line:

 OPENSSL_CONF=example.cnf openssl asn1parse -genstr OID:1.2.3.4.1

will output:

 0:d=0  hl=2 l=   4 prim: OBJECT            :newoid1

showing that the OID "newoid1" has been added as "1.2.3.4.1".

=head2 Provider Configuration

The name B<providers> in the initialization section names the section
containing cryptographic provider configuration. The name/value assignments
in this section each name a provider, and point to the configuration section
for that provider. The provider-specific section is used to specify how
to load the module, activate it, and set other parameters.

Within a provider section, the following names have meaning:

=over 4

=item B<identity>

This is used to specify an alternate name, overriding the default name
specified in the list of providers.  For example:

 [providers]
 foo = foo_provider

 [foo_provider]
 identity = my_fips_module

=item B<module>

Specifies the pathname of the module (typically a shared library) to load.

=item B<activate>

If present and set to one of the values yes, on, true or 1, then the associated
provider will be activated. Conversely, setting this value to no, off, false, or
0 will prevent the provider from being activated. Settings can be given in lower
or uppercase. Setting activate to any other setting, or omitting a setting
value will result in an error.

= item B<soft_load>

If enabled, informs the library to clear the error stack on failure to activate
requested provider.  A value of 1, yes, true or on (in lower or uppercase) will
activate this setting, while a value of 0, no, false, or off (again in lower or
uppercase) will disable this setting.  Any other value will produce an error.
Note this setting defaults to off if not provided

=back

All parameters in the section as well as sub-sections are made
available to the provider.

=head3 Default provider and its activation

If no providers are activated explicitly, the default one is activated implicitly.
See L<OSSL_PROVIDER-default(7)> for more details.

If you add a section explicitly activating any other provider(s),
you most probably need to explicitly activate the default provider,
otherwise it becomes unavailable in openssl. It may make the system remotely unavailable.

=head2 EVP Configuration

The name B<alg_section> in the initialization section names the section
containing algorithmic properties when using the B<EVP> API.

Within the algorithm properties section, the following names have meaning:

=over 4

=item B<default_properties>

The value may be anything that is acceptable as a property query
string for EVP_set_default_properties().

=item B<fips_mode> (deprecated)

The value is a boolean that can be B<yes> or B<no>.  If the value is
B<yes>, this is exactly equivalent to:

 default_properties = fips=yes

If the value is B<no>, nothing happens. Using this name is deprecated, and
if used, it must be the only name in the section.

=back

=head2 SSL Configuration

The name B<ssl_conf> in the initialization section names the section
containing the list of SSL/TLS configurations.
As with the providers, each name in this section identifies a
section with the configuration for that name. For example:

 [ssl_configuration]
 server = server_tls_config
 client = client_tls_config
 system_default = tls_system_default

 [server_tls_config]
 ... configuration for SSL/TLS servers ...

 [client_tls_config]
 ... configuration for SSL/TLS clients ...

The configuration name B<system_default> has a special meaning.  If it
exists, it is applied whenever an B<SSL_CTX> object is created.  For example,
to impose system-wide minimum TLS and DTLS protocol versions:

 [tls_system_default]
 MinProtocol = TLSv1.2
 MinProtocol = DTLSv1.2

The minimum TLS protocol is applied to B<SSL_CTX> objects that are TLS-based,
and the minimum DTLS protocol to those are DTLS-based.
The same applies also to maximum versions set with B<MaxProtocol>.

Each configuration section consists of name/value pairs that are parsed
by B<SSL_CONF_cmd(3)>, which will be called by SSL_CTX_config() or
SSL_config(), appropriately.  Note that any characters before an initial
dot in the configuration section are ignored, so that the same command can
be used multiple times. This probably is most useful for loading different
key types, as shown here:

 [server_tls_config]
 RSA.Certificate = server-rsa.pem
 ECDSA.Certificate = server-ecdsa.pem

=head2 Random Configuration

The name B<random> in the initialization section names the section
containing the random number generator settings.

Within the random section, the following names have meaning:

=over 4

=item B<random>

This is used to specify the random bit generator.
For example:

 [random]
 random = CTR-DRBG

The available random bit generators are:

=over 4

=item B<CTR-DRBG>

=item B<HASH-DRBG>

=item B<HMAC-DRBG>

=back

=item B<cipher>

This specifies what cipher a B<CTR-DRBG> random bit generator will use.
Other random bit generators ignore this name.
The default value is B<AES-256-CTR>.

=item B<digest>

This specifies what digest the B<HASH-DRBG> or B<HMAC-DRBG> random bit
generators will use.  Other random bit generators ignore this name.

=item B<properties>

This sets the property query used when fetching the random bit generator and
any underlying algorithms.

=item B<seed>

This sets the randomness source that should be used.  By default B<SEED-SRC>
will be used outside of the FIPS provider.  The FIPS provider uses call backs
to access the same randomness sources from outside the validated boundary.

=item B<seed_properties>

This sets the property query used when fetching the randomness source.

=item B<random_provider>

This sets the provider to use for the L<RAND_bytes(3)> calls instead of the built-in
entropy sources.  It defaults to "fips".  If the named provider is not loaded, the
built-in entropy sources will be used.

=back

=head1 EXAMPLES

This example shows how to use quoting and escaping.

 # This is the default section.
 HOME = /temp
 configdir = $ENV::HOME/config

 [ section_one ]
 # Quotes permit leading and trailing whitespace
 any = " any variable name "
 other = A string that can \
 cover several lines \
 by including \\ characters
 message = Hello World\n

 [ section_two ]
 greeting = $section_one::message

This example shows how to expand environment variables safely.
In this example, the variable B<tempfile> is intended to refer
to a temporary file, and the environment variable B<TEMP> or
B<TMP>, if present, specify the directory where the file
should be put.
Since the default section is checked if a variable does not
exist, it is possible to set B<TMP> to default to F</tmp>, and
B<TEMP> to default to B<TMP>.

 # These two lines must be in the default section.
 TMP = /tmp
 TEMP = $ENV::TMP

 # This can be used anywhere
 tmpfile = ${ENV::TEMP}/tmp.filename

This example shows how to enforce FIPS mode for the application
F<sample>.

 sample = fips_config

 [fips_config]
 alg_section = evp_properties

 [evp_properties]
 default_properties = "fips=yes"

=head1 ENVIRONMENT

=over 4

=item B<OPENSSL_CONF>

The path to the config file, or the empty string for none.
Ignored in set-user-ID and set-group-ID programs.

=item B<OPENSSL_MODULES>

The path to the directory with OpenSSL modules, such as providers.
Ignored in set-user-ID and set-group-ID programs.

=item B<OPENSSL_CONF_INCLUDE>

The optional path to prepend to all B<.include> paths.

=back

=head1 BUGS

There is no way to include characters using the octal B<\nnn> form. Strings
are all null terminated so nulls cannot form part of the value.

The escaping isn't quite right: if you want to use sequences like B<\n>
you can't use any quote escaping on the same line.

The limit that only one directory can be opened and read at a time
can be considered a bug and should be fixed.

=head1 HISTORY

An undocumented API, NCONF_WIN32(), used a slightly different set
of parsing rules there were intended to be tailored to
the Microsoft Windows platform.
Specifically, the backslash character was not an escape character and
could be used in pathnames, only the double-quote character was recognized,
and comments began with a semi-colon.
This function was deprecated in OpenSSL 3.0; applications with
configuration files using that syntax will have to be modified.

The I<engines> parameter was removed in OpenSSL 4.0.

=head1 SEE ALSO

L<openssl-x509(1)>, L<openssl-req(1)>, L<openssl-ca(1)>,
L<openssl-fipsinstall(1)>,
L<ASN1_generate_nconf(3)>,
L<EVP_set_default_properties(3)>,
L<CONF_modules_load(3)>,
L<CONF_modules_load_file(3)>,
L<OPENSSL_INIT_set_config_appname(3)>,
L<OPENSSL_init_crypto(3)>,
L<OPENSSL_init_ssl(3)>,
L<RAND_bytes(3)>,
L<fips_config(5)>, and
L<x509v3_config(5)>.

=head1 COPYRIGHT

Copyright 2000-2026 The OpenSSL Project Authors. All Rights Reserved.

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
L<https://www.openssl.org/source/license.html>.

=cut
