Manpages - config.5ssl

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config - OpenSSL CONF library configuration files


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.


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.:

[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.

ASN1 Object Configuration Module

This module has the name 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, the value is the numerical form of the OID. Although some of the openssl utility sub commands already have their own ASN1 OBJECT section functionality not all do. By using the ASN1 OBJECT configuration module all the openssl utility sub commands can see the new objects as well as any compliant applications. For example:

[new_oids] some_new_oid = some_other_oid =

It is also possible to set the value to the long name followed by a comma and the numerical OID form. For example:

shortName = some object long name,

Engine Configuration Module

This ENGINE configuration module has the name engines. The value of this variable points to a section containing further ENGINE configuration information.

The section pointed to by engines is a table of engine names (though see engine_id below) and further sections containing configuration information specific to each ENGINE.

Each ENGINE specific section is used to set default algorithms, load dynamic, perform initialization and send ctrls. The actual operation performed depends on the command name which is the name of the name value pair. The currently supported commands are listed below.

For example:

[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 …

The command engine_id is used to give the ENGINE name. If used this command must be first. For example:

[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

The command dynamic_path loads and adds an ENGINE from the given path. It is equivalent to sending the ctrls SO_PATH with the path argument followed by LIST_ADD with value 2 and LOAD to the dynamic ENGINE. If this is not the required behaviour then alternative ctrls can be sent directly to the dynamic ENGINE using ctrl commands.

The command init determines whether to initialize the ENGINE. If the value is 0 the ENGINE will not be initialized, if 1 and attempt it made to initialized the ENGINE immediately. If the init command is not present then an attempt will be made to initialize the ENGINE after all commands in its section have been processed.

The command default_algorithms sets the default algorithms an ENGINE will supply using the functions ENGINE_set_default_string().

If the name matches none of the above command names it is assumed to be a ctrl command which is sent to the ENGINE. The value of the command is the argument to the ctrl command. If the value is the string EMPTY then no value is sent to the command.

For example:

[engine_section] # Configure ENGINE named “foo” foo = foo_section [foo_section] # Load engine from DSO dynamic_path = /some/path/ # A foo specific ctrl. some_ctrl = some_value # Another ctrl that doesnt take a value. other_ctrl = EMPTY # Supply all default algorithms default_algorithms = ALL

EVP Configuration Module

This modules has the name alg_section which points to a section containing algorithm commands.

Currently the only algorithm command supported is fips_mode whose value can only be the boolean string off. If fips_mode is set to on, an error occurs as this library version is not FIPS capable.

SSL Configuration Module

This module has the name ssl_conf which points to a section containing SSL configurations.

Each line in the SSL configuration section contains the name of the configuration and the section containing it.

Each configuration section consists of command value pairs for SSL_CONF. Each pair will be passed to a SSL_CTX or SSL structure if it calls SSL_CTX_config() or SSL_config() with the appropriate configuration name.

Note: any characters before an initial dot in the configuration section are ignored so the same command can be used multiple times.

For example:

ssl_conf = ssl_sect [ssl_sect] server = server_section [server_section] RSA.Certificate = server-rsa.pem ECDSA.Certificate = server-ecdsa.pem Ciphers = ALL:!RC4

The system default configuration with name system_default if present will be applied during any creation of the SSL_CTX structure.

Example of a configuration with the system default:

ssl_conf = ssl_sect [ssl_sect] system_default = system_default_sect [system_default_sect] MinProtocol = TLSv1.2 MinProtocol = DTLSv1.2


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”


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

configdir=$ENV::HOME/config [ section_one ] # We are now in section one.

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 isnt in the environment TEMP=\(ENV::TMP # The above value is used if TEMP isnt in the environment tmpfile=\){ENV::TEMP}/tmp.filename

Simple OpenSSL library configuration example to enter FIPS mode:

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.

Simple OpenSSL library configuration to make TLS 1.2 and DTLS 1.2 the system-default minimum TLS and DTLS versions, respectively:

default_conf_section [default_conf_section] # We only specify configuration for the “ssl module” ssl_conf = ssl_section [ssl_section] system_default = system_default_section [system_default_section] MinProtocol = TLSv1.2 MinProtocol = DTLSv1.2

The minimum TLS protocol is applied to 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 MaxProtocol.

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

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 = # New OID shortname and long name newoid2 = New OID 2 long name,

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:

will output:

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

showing that the OID newoid1 has been added as


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


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 a variable expansion will only work if the variables referenced are defined earlier in the file.


x509 (1), req (1), ca (1)


Copyright 2000-2020 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

Author: dt

Created: 2022-02-20 Sun 09:35