config

Description

The OpenSSL CONF library can be used to read configuration files. It is used for the OpenSSL master configuration file openssl.cnf and in a few other places like SPKAC files and certificate extension files for the x509 utility. OpenSSL applications can also use the CONF library for their own purposes.

A configuration file is divided into a number of sections. Each section starts with a line [ section_name ] and ends when a new section is started or end of file is reached. A section name can consist of alphanumeric characters and underscores.

The first section of a configuration file is special and is referred to as the default section. This section is usually unnamed and spans from the start of file until the first named section. When a name is being looked up it is first looked up in a named section (if any) and then the default section.

The environment is mapped onto a section called ENV.

Comments can be included by preceding them with the # character

Other files can be included using the .include directive followed by a path. If the path points to a directory all files with names ending with .cnf or .conf are included from the directory. Recursive inclusion of directories from files in such directory is not supported. That means the files in the included directory can also contain .include directives but only inclusion of regular files is supported there. The inclusion of directories is not supported on systems without POSIX IO support.

It is strongly recommended to use absolute paths with the .include directive. Relative paths are evaluated based on the application current working directory so unless the configuration file containing the .include directive is application specific the inclusion will not work as expected.

There can be optional = character and whitespace characters between .include directive and the path which can be useful in cases the configuration file needs to be loaded by old OpenSSL versions which do not support the .include syntax. They would bail out with error if the = character is not present but with it they just ignore the include.

Each section in a configuration file consists of a number of name and value pairs of the form name=value

The name string can contain any alphanumeric characters as well as a few punctuation symbols such as . , ; and _.

The value string consists of the string following the = character until end of line with any leading and trailing white space removed.

The value string undergoes variable expansion. This can be done by including the form $var or ${var}: 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 $section::name or ${section::name}. By using the form $ENV::name environment variables can be substituted. It is also possible to assign values to environment variables by using the name ENV::name, this will work if the program looks up environment variables using the CONF library instead of calling getenv() directly. The value string must not exceed 64k in length after variable expansion. Otherwise an error will occur.

It is possible to escape certain characters by using any kind of quote or the \ character. By making the last character of a line a \ a value string can be spread across multiple lines. In addition the sequences \n, \r, \b and \t are recognized.

All expansion and escape rules as described above that apply to value also apply to the path of the .include directive.

Openssl Library Configuration

Applications can automatically configure certain aspects of OpenSSL using the master OpenSSL configuration file, or optionally an alternative configuration file. The openssl 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.

To enable library configuration the default section needs to contain an appropriate line which points to the main configuration section. The default name is openssl_conf which is used by the openssl utility. Other applications may use an alternative name such as myapplication_conf. All library configuration lines appear in the default section at the start of the configuration file.

The configuration section should consist of a set of name value pairs which contain specific module configuration information. The name represents the name of the configuration module. The meaning of the value is module specific: it may, for example, represent a further configuration section containing configuration module specific information. E.g.:

 # This must be in the default section
 openssl_conf = openssl_init

 [openssl_init]

 oid_section = new_oids
 engines = engine_section

 [new_oids]

 ... new oids here ...

 [engine_section]

 ... engine stuff here ...

The features of each configuration module are described below.

 [new_oids]

 some_new_oid = 1.2.3.4
 some_other_oid = 1.2.3.5

 shortName = some object long name, 1.2.3.4

 [engine_section]

 # Configure ENGINE named "foo"
 foo = foo_section
 # Configure ENGINE named "bar"
 bar = bar_section

 [foo_section]
 ... foo ENGINE specific commands ...

 [bar_section]
 ... "bar" ENGINE specific commands ...

 [engine_section]
 # This would normally handle an ENGINE named "foo"
 foo = foo_section

 [foo_section]
 # Override default name and use "myfoo" instead.
 engine_id = myfoo

 [engine_section]

 # Configure ENGINE named "foo"
 foo = foo_section

 [foo_section]
 # Load engine from DSO
 dynamic_path = /some/path/fooengine.so
 # A foo specific ctrl.
 some_ctrl = some_value
 # Another ctrl that doesn't take a value.
 other_ctrl = EMPTY
 # Supply all default algorithms
 default_algorithms = ALL

 ssl_conf = ssl_sect

 [ssl_sect]

 server = server_section

 [server_section]

 RSA.Certificate = server-rsa.pem
 ECDSA.Certificate = server-ecdsa.pem
 Ciphers = ALL:!RC4

 ssl_conf = ssl_sect

 [ssl_sect]

 system_default = system_default_sect

 [system_default_sect]

 MinProtocol = TLSv1.2

Notes

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 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 HOME which may not be defined on non Unix systems and would cause an error.

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 Examples section for an example of how to do this.

If the same variable exists 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 . e.g.

 1.OU="My first OU"
 2.OU="My Second OU"

Examples

Here is a sample configuration file using some of the features mentioned above.

 # 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 \
 cover several lines \
 by including \\ characters

 message = Hello World\n

 [ section_two ]

 greeting = $section_one::message

This next example shows how to expand environment variables safely.

Suppose you want a variable called tmpfile to refer to a temporary filename. The directory it is placed in can determined by the TEMP or 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 TEMP taking priority and /tmp used if neither is defined:

 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

Simple OpenSSL library configuration example to enter FIPS mode:

 # 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
 alg_section = evp_sect

 [evp_sect]
 # Set to "yes" to enter FIPS mode if supported
 fips_mode = yes

Note: in the above example you will get an error in non FIPS capable versions of OpenSSL.

More complex OpenSSL library configuration. Add OID and don't enter FIPS mode:

 # 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
 alg_section = evp_sect
 oid_section = new_oids

 [evp_sect]
 # This will have no effect as FIPS mode is off by default.
 # Set to "yes" to enter FIPS mode, if supported
 fips_mode = no

 [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

The above examples can be used with any application supporting library configuration if “openssl_conf” is modified to match the appropriate “appname”.

For example if the second sample file above is saved to “example.cnf” then the 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”.

Environment

OPENSSL_CONF

The path to the config file. Ignored in set-user-ID and set-group-ID programs.

OPENSSL_ENGINES

The path to the engines directory. Ignored in set-user-ID and set-group-ID programs.

Bugs

Currently there is no way to include characters using the octal \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 \n you can't use any quote escaping on the same line.

Files are loaded in a single pass. This means that an variable expansion will only work if the variables referenced are defined earlier in the file.

See Also

x509(1), req(1), ca(1)

Copyright

Copyright 2000-2019 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>.

Referenced By

ca.1ssl(1), CA.pl.1ssl(1), CONF_modules_free.3ssl(3), CONF_modules_load_file.3ssl(3), engine.1ssl(1), ENGINE_add.3ssl(3), openssl.1ssl(1), OPENSSL_config.3ssl(3), OPENSSL_load_builtin_modules.3ssl(3), req.1ssl(1), SSL_CTX_config.3ssl(3), ts.1ssl(1).

The man page openssl.cnf.5ssl(5) is an alias of config.5ssl(5).