Ubuntu Manpage: fips_module - OpenSSL fips module guide

Provided by: openssl_3.0.13-0ubuntu3.4_amd64

NAME

       fips_module - OpenSSL fips module guide

SYNOPSIS

       See the individual manual pages for details.

DESCRIPTION

This guide details different ways that OpenSSL can be used in conjunction with the FIPS
module. Which is the correct approach to use will depend on your own specific
circumstances and what you are attempting to achieve.

For information related to installing the FIPS module see
<https://github.com/openssl/openssl/blob/master/README-FIPS.md>.

Note that the old functions FIPS_mode() and FIPS_mode_set() are no longer present so you
must remove them from your application if you use them.

Applications written to use the OpenSSL 3.0 FIPS module should not use any legacy APIs or
features that avoid the FIPS module. Specifically this includes:

• Low level cryptographic APIs (use the high level APIs, such as EVP, instead)

• Engines

• Any functions that create or modify custom "METHODS" (for example EVP_MD_meth_new(),
EVP_CIPHER_meth_new(), EVP_PKEY_meth_new(), RSA_meth_new(), EC_KEY_METHOD_new(), etc.)

All of the above APIs are deprecated in OpenSSL 3.0 - so a simple rule is to avoid using
all deprecated functions. See migration_guide(7) for a list of deprecated functions.

Applications running on systems operating in FIPS-approved mode
When running on systems that are operating in FIPS-approved mode and no providers are
loaded explicitly via the application or config, the FIPS module is loaded implicitly as a
fallback provider whenever an algorithm is fetched for the first time. The "default"
provider is not loaded implicitly in this case, and must be loaded explicitly if it is
required by an application.

Every OSSL_LIB_CTX(3) is created with "fips=yes" as a default property in this mode so
that algorithm fetches will only fetch algorithms that define this property and are FIPS-
approved. To use algorithms that are not FIPS approved, either specify "-fips" or
"fips=no" as a property query string with fetching functions, or use the
EVP_default_properties_enable_fips(3) function to remove the default property for a
specific OSSL_LIB_CTX.

Making all applications use the FIPS module by default
One simple approach is to cause all applications that are using OpenSSL to only use the
FIPS module for cryptographic algorithms by default.

This approach can be done purely via configuration. As long as applications are built and
linked against OpenSSL 3.0 and do not override the loading of the default config file or
its settings then they can automatically start using the FIPS module without the need for
any further code changes.

To do this the default OpenSSL config file will have to be modified. The location of this
config file will depend on the platform, and any options that were given during the build
process. You can check the location of the config file by running this command:

$ openssl version -d
OPENSSLDIR: "/usr/local/ssl"

Caution: Many Operating Systems install OpenSSL by default. It is a common error to not
have the correct version of OpenSSL in your $PATH. Check that you are running an OpenSSL
3.0 version like this:

$ openssl version -v
OpenSSL 3.0.0-dev xx XXX xxxx (Library: OpenSSL 3.0.0-dev xx XXX xxxx)

The OPENSSLDIR value above gives the directory name for where the default config file is
stored. So in this case the default config file will be called /usr/local/ssl/openssl.cnf.

Edit the config file to add the following lines near the beginning:

config_diagnostics = 1
openssl_conf = openssl_init

.include /usr/local/ssl/fipsmodule.cnf

[openssl_init]
providers = provider_sect

[provider_sect]
fips = fips_sect
base = base_sect

[base_sect]
activate = 1

Obviously the include file location above should match the path and name of the FIPS
module config file that you installed earlier. See
<https://github.com/openssl/openssl/blob/master/README-FIPS.md>.

For FIPS usage, it is recommended that the config_diagnostics option is enabled to prevent
accidental use of non-FIPS validated algorithms via broken or mistaken configuration. See
config(5).

Any applications that use OpenSSL 3.0 and are started after these changes are made will
start using only the FIPS module unless those applications take explicit steps to avoid
this default behaviour. Note that this configuration also activates the "base" provider.
The base provider does not include any cryptographic algorithms (and therefore does not
impact the validation status of any cryptographic operations), but does include other
supporting algorithms that may be required. It is designed to be used in conjunction with
the FIPS module.

This approach has the primary advantage that it is simple, and no code changes are
required in applications in order to benefit from the FIPS module. There are some
disadvantages to this approach:

• You may not want all applications to use the FIPS module.

It may be the case that some applications should and some should not use the FIPS
module.

• If applications take explicit steps to not load the default config file or set
different settings.

This method will not work for these cases.

• The algorithms available in the FIPS module are a subset of the algorithms that are
available in the default OpenSSL Provider.

If any applications attempt to use any algorithms that are not present, then they will
fail.

• Usage of certain deprecated APIs avoids the use of the FIPS module.

If any applications use those APIs then the FIPS module will not be used.

Selectively making applications use the FIPS module by default
A variation on the above approach is to do the same thing on an individual application
basis. The default OpenSSL config file depends on the compiled in value for OPENSSLDIR as
described in the section above. However it is also possible to override the config file to
be used via the OPENSSL_CONF environment variable. For example the following, on Unix,
will cause the application to be executed with a non-standard config file location:

$ OPENSSL_CONF=/my/nondefault/openssl.cnf myapplication

Using this mechanism you can control which config file is loaded (and hence whether the
FIPS module is loaded) on an application by application basis.

This removes the disadvantage listed above that you may not want all applications to use
the FIPS module. All the other advantages and disadvantages still apply.

Programmatically loading the FIPS module (default library context)
Applications may choose to load the FIPS provider explicitly rather than relying on config
to do this. The config file is still necessary in order to hold the FIPS module config
data (such as its self test status and integrity data). But in this case we do not
automatically activate the FIPS provider via that config file.

To do things this way configure as per "Making all applications use the FIPS module by
default" above, but edit the fipsmodule.cnf file to remove or comment out the line which
says "activate = 1" (note that setting this value to 0 is not sufficient). This means all
the required config information will be available to load the FIPS module, but it is not
automatically loaded when the application starts. The FIPS provider can then be loaded
programmatically like this:

#include <openssl/provider.h>

int main(void)
{
OSSL_PROVIDER *fips;
OSSL_PROVIDER *base;

fips = OSSL_PROVIDER_load(NULL, "fips");
if (fips == NULL) {
printf("Failed to load FIPS provider\n");
exit(EXIT_FAILURE);
}
base = OSSL_PROVIDER_load(NULL, "base");
if (base == NULL) {
OSSL_PROVIDER_unload(fips);
printf("Failed to load base provider\n");
exit(EXIT_FAILURE);
}

/* Rest of application */

OSSL_PROVIDER_unload(base);
OSSL_PROVIDER_unload(fips);
exit(EXIT_SUCCESS);
}

Note that this should be one of the first things that you do in your application. If any
OpenSSL functions get called that require the use of cryptographic functions before this
occurs then, if no provider has yet been loaded, then the default provider will be
automatically loaded. If you then later explicitly load the FIPS provider then you will
have both the FIPS and the default provider loaded at the same time. It is undefined which
implementation of an algorithm will be used if multiple implementations are available and
you have not explicitly specified via a property query (see below) which one should be
used.

Also note that in this example we have additionally loaded the "base" provider. This
loads a sub-set of algorithms that are also available in the default provider -
specifically non cryptographic ones which may be used in conjunction with the FIPS
provider. For example this contains algorithms for encoding and decoding keys. If you
decide not to load the default provider then you will usually want to load the base
provider instead.

In this example we are using the "default" library context. OpenSSL functions operate
within the scope of a library context. If no library context is explicitly specified then
the default library context is used. For further details about library contexts see the
OSSL_LIB_CTX(3) man page.

Loading the FIPS module at the same time as other providers
It is possible to have the FIPS provider and other providers (such as the default
provider) all loaded at the same time into the same library context. You can use a
property query string during algorithm fetches to specify which implementation you would
like to use.

For example to fetch an implementation of SHA256 which conforms to FIPS standards you can
specify the property query "fips=yes" like this:

EVP_MD *sha256;

sha256 = EVP_MD_fetch(NULL, "SHA2-256", "fips=yes");

If no property query is specified, or more than one implementation matches the property
query then it is undefined which implementation of a particular algorithm will be
returned.

This example shows an explicit request for an implementation of SHA256 from the default
provider:

EVP_MD *sha256;

sha256 = EVP_MD_fetch(NULL, "SHA2-256", "provider=default");

It is also possible to set a default property query string. The following example sets the
default property query of "fips=yes" for all fetches within the default library context:

EVP_set_default_properties(NULL, "fips=yes");

If a fetch function has both an explicit property query specified, and a default property
query is defined then the two queries are merged together and both apply. The local
property query overrides the default properties if the same property name is specified in
both.

There are two important built-in properties that you should be aware of:

The "provider" property enables you to specify which provider you want an implementation
to be fetched from, e.g. "provider=default" or "provider=fips". All algorithms
implemented in a provider have this property set on them.

There is also the "fips" property. All FIPS algorithms match against the property query
"fips=yes". There are also some non-cryptographic algorithms available in the default and
base providers that also have the "fips=yes" property defined for them. These are the
encoder and decoder algorithms that can (for example) be used to write out a key generated
in the FIPS provider to a file. The encoder and decoder algorithms are not in the FIPS
module itself but are allowed to be used in conjunction with the FIPS algorithms.

It is possible to specify default properties within a config file. For example the
following config file automatically loads the default and FIPS providers and sets the
default property value to be "fips=yes". Note that this config file does not load the
"base" provider. All supporting algorithms that are in "base" are also in "default", so it
is unnecessary in this case:

config_diagnostics = 1
openssl_conf = openssl_init

.include /usr/local/ssl/fipsmodule.cnf

[openssl_init]
providers = provider_sect
alg_section = algorithm_sect

[provider_sect]
fips = fips_sect
default = default_sect

[default_sect]
activate = 1

[algorithm_sect]
default_properties = fips=yes

Programmatically loading the FIPS module (nondefault library context)
In addition to using properties to separate usage of the FIPS module from other usages
this can also be achieved using library contexts. In this example we create two library
contexts. In one we assume the existence of a config file called openssl-fips.cnf that
automatically loads and configures the FIPS and base providers. The other library context
will just use the default provider.

OSSL_LIB_CTX *fips_libctx, *nonfips_libctx;
OSSL_PROVIDER *defctxnull = NULL;
EVP_MD *fipssha256 = NULL, *nonfipssha256 = NULL;
int ret = 1;

/*
* Create two nondefault library contexts. One for fips usage and
* one for non-fips usage
*/
fips_libctx = OSSL_LIB_CTX_new();
nonfips_libctx = OSSL_LIB_CTX_new();
if (fips_libctx == NULL || nonfips_libctx == NULL)
goto err;

/* Prevent anything from using the default library context */
defctxnull = OSSL_PROVIDER_load(NULL, "null");

/*
* Load config file for the FIPS library context. We assume that
* this config file will automatically activate the FIPS and base
* providers so we don't need to explicitly load them here.
*/
if (!OSSL_LIB_CTX_load_config(fips_libctx, "openssl-fips.cnf"))
goto err;

/*
* We don't need to do anything special to load the default
* provider into nonfips_libctx. This happens automatically if no
* other providers are loaded.
* Because we don't call OSSL_LIB_CTX_load_config() explicitly for
* nonfips_libctx it will just use the default config file.
*/

/* As an example get some digests */

/* Get a FIPS validated digest */
fipssha256 = EVP_MD_fetch(fips_libctx, "SHA2-256", NULL);
if (fipssha256 == NULL)
goto err;

/* Get a non-FIPS validated digest */
nonfipssha256 = EVP_MD_fetch(nonfips_libctx, "SHA2-256", NULL);
if (nonfipssha256 == NULL)
goto err;

/* Use the digests */

printf("Success\n");
ret = 0;

err:
EVP_MD_free(fipssha256);
EVP_MD_free(nonfipssha256);
OSSL_LIB_CTX_free(fips_libctx);
OSSL_LIB_CTX_free(nonfips_libctx);
OSSL_PROVIDER_unload(defctxnull);

return ret;

Note that we have made use of the special "null" provider here which we load into the
default library context. We could have chosen to use the default library context for FIPS
usage, and just create one additional library context for other usages - or vice versa.
However if code has not been converted to use library contexts then the default library
context will be automatically used. This could be the case for your own existing
applications as well as certain parts of OpenSSL itself. Not all parts of OpenSSL are
library context aware. If this happens then you could "accidentally" use the wrong library
context for a particular operation. To be sure this doesn't happen you can load the "null"
provider into the default library context. Because a provider has been explicitly loaded,
the default provider will not automatically load. This means code using the default
context by accident will fail because no algorithms will be available.

See "Library Context" in migration_guide(7) for additional information about the Library
Context.

Using Encoders and Decoders with the FIPS module
Encoders and decoders are used to read and write keys or parameters from or to some
external format (for example a PEM file). If your application generates keys or parameters
that then need to be written into PEM or DER format then it is likely that you will need
to use an encoder to do this. Similarly you need a decoder to read previously saved keys
and parameters. In most cases this will be invisible to you if you are using APIs that
existed in OpenSSL 1.1.1 or earlier such as i2d_PrivateKey(3). However the appropriate
encoder/decoder will need to be available in the library context associated with the key
or parameter object. The built-in OpenSSL encoders and decoders are implemented in both
the default and base providers and are not in the FIPS module boundary. However since they
are not cryptographic algorithms themselves it is still possible to use them in
conjunction with the FIPS module, and therefore these encoders/decoders have the
"fips=yes" property against them. You should ensure that either the default or base
provider is loaded into the library context in this case.

Using the FIPS module in SSL/TLS
Writing an application that uses libssl in conjunction with the FIPS module is much the
same as writing a normal libssl application. If you are using global properties and the
default library context to specify usage of FIPS validated algorithms then this will
happen automatically for all cryptographic algorithms in libssl. If you are using a
nondefault library context to load the FIPS provider then you can supply this to libssl
using the function SSL_CTX_new_ex(3). This works as a drop in replacement for the function
SSL_CTX_new(3) except it provides you with the capability to specify the library context
to be used. You can also use the same function to specify libssl specific properties to
use.

In this first example we create two SSL_CTX objects using two different library contexts.

/*
* We assume that a nondefault library context with the FIPS
* provider loaded has been created called fips_libctx.
*/
SSL_CTX *fips_ssl_ctx = SSL_CTX_new_ex(fips_libctx, NULL, TLS_method());
/*
* We assume that a nondefault library context with the default
* provider loaded has been created called non_fips_libctx.
*/
SSL_CTX *non_fips_ssl_ctx = SSL_CTX_new_ex(non_fips_libctx, NULL,
TLS_method());

In this second example we create two SSL_CTX objects using different properties to specify
FIPS usage:

/*
* The "fips=yes" property includes all FIPS approved algorithms
* as well as encoders from the default provider that are allowed
* to be used. The NULL below indicates that we are using the
* default library context.
*/
SSL_CTX *fips_ssl_ctx = SSL_CTX_new_ex(NULL, "fips=yes", TLS_method());
/*
* The "provider!=fips" property allows algorithms from any
* provider except the FIPS provider
*/
SSL_CTX *non_fips_ssl_ctx = SSL_CTX_new_ex(NULL, "provider!=fips",
TLS_method());

Confirming that an algorithm is being provided by the FIPS module
A chain of links needs to be followed to go from an algorithm instance to the provider
that implements it. The process is similar for all algorithms. Here the example of a
digest is used.

To go from an EVP_MD_CTX to an EVP_MD, use EVP_MD_CTX_md(3) . To go from the EVP_MD to
its OSSL_PROVIDER, use EVP_MD_get0_provider(3). To extract the name from the
OSSL_PROVIDER, use OSSL_PROVIDER_get0_name(3).

NOTES

       Some released versions of OpenSSL do not include a validated FIPS provider.  To determine
       which versions have undergone the validation process, please refer to the OpenSSL
       Downloads page <https://www.openssl.org/source/>.  If you require FIPS-approved
       functionality, it is essential to build your FIPS provider using one of the validated
       versions listed there.  Normally, it is possible to utilize a FIPS provider constructed
       from one of the validated versions alongside libcrypto and libssl compiled from any
       release within the same major release series.  This flexibility enables you to address bug
       fixes and CVEs that fall outside the FIPS boundary.

HISTORY

       The FIPS module guide was created for use with the new FIPS provider in OpenSSL 3.0.

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