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config(5) 1/Mar/2004 (0.9.7e) config(5)
NAME
config - OpenSSL CONF library configuration files
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 is usually unnamed
and is 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
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.
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.
OPENSSL LIBRARY CONFIGURATION
In OpenSSL 0.9.7 and later 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 myapplicaton_conf.
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_conf = openssl_init
[openssl_init]
oid_section = new_oids
engines = engine_section
[new_oids]
... new oids here ...
[engine_section]
... engine stuff here ...
Currently there are two configuration modules. One for ASN1
objects another for ENGINE configuration.
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 = 1.2.3.4
some_other_oid = 1.2.3.5
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 informations 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/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
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 = $section_one::message
This next example shows how to expand environment variables
safely.
Suppose you want a variable called tmpfile to refer to a
temporary filename. The directory it is placed in can
determined by the the TEMP or TMP environment variables but
they may not be set to any value at all. If you just include
the environment variable names and the variable doesn't
exist then this will cause an error when an attempt is made
to load the configuration file. By making use of the default
section both values can be looked up with TEMP taking
priority and /tmp used if neither is defined:
TMP=/tmp
# The above value is used if TMP isn't in the environment
TEMP=$ENV::TMP
# The above value is used if TEMP isn't in the environment
tmpfile=${ENV::TEMP}/tmp.filename
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)
Page 6 (printed 10/20/05)