Ubuntu Manpage: fips_module - OpenSSL fips module guide

Provided by: openssl_3.4.1-1ubuntu3_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 ossl-guide-migration(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
alg_section = algorithm_sect

[provider_sect]
fips = fips_sect
base = base_sect

[base_sect]
activate = 1

[algorithm_sect]
default_properties = fips=yes

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 unspecified 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
unspecified 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;

/*
* Set the default property query on the FIPS library context to
* ensure that only FIPS algorithms can be used. There are a few non-FIPS
* approved algorithms in the FIPS provider for backward compatibility reasons.
*/
if (!EVP_set_default_properties(fips_libctx, "fips=yes"))
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 ossl-guide-migration(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, "fips=yes", 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).

FIPS indicators
FIPS indicators have been added to the FIPS provider in OpenSSL 3.4. FIPS 140-3 requires indicators to
be used if the FIPS provider allows non approved algorithms. An algorithm is approved if it passes all
required checks such as minimum key size. By default an error will occur if any check fails. For
backwards compatibility individual algorithms may override the checks by using either an option in the
FIPS configuration (See "FIPS indicator options" in fips_config(5)) OR in code using an algorithm context
setter. Overriding the check means that the algorithm is not FIPS compliant.
OSSL_INDICATOR_set_callback(3) can be called to register a callback to log unapproved algorithms. At the
end of any algorithm operation the approved status can be queried using an algorithm context getter to
retrieve the indicator (e.g. "fips-indicator"). An example of an algorithm context setter is "key-check"
in "Supported parameters" in EVP_KDF-HKDF(7).

The following algorithms use "fips-indicator" to query if the algorithm is approved:

DSA Key generation
DSA Key generation is no longer approved. See "DSA parameters" in EVP_PKEY-DSA(7)

DSA Signatures
DSA Signature generation is no longer approved. See "Signature Parameters" in EVP_SIGNATURE-DSA(7)

ECDSA Signatures
See "ECDSA Signature Parameters" in EVP_SIGNATURE-ECDSA(7)

EC Key Generation
See "Common EC parameters" in EVP_PKEY-EC(7)

RSA Encryption
"pkcs1" padding is no longer approved.

See "RSA Asymmetric Cipher parameters" in EVP_ASYM_CIPHER-RSA(7) and "RSA KEM parameters" in
EVP_KEM-RSA(7)

RSA Signatures
See "Signature Parameters" in EVP_SIGNATURE-RSA(7)

DRBGS
See "Supported parameters" in EVP_RAND-HASH-DRBG(7) and EVP_RAND-HMAC-DRBG(7)/Supported parameters>

DES Triple-DES is not longer approved for encryption. See "Parameters" in EVP_CIPHER-DES(7)

DH See "DH and DHX key exchange parameters" in EVP_KEYEXCH-DH(7)

ECDH
See "ECDH Key Exchange parameters" in EVP_KEYEXCH-ECDH(7)

KDFS
See relevant KDF documentation e.g. "Supported parameters" in EVP_KDF-HKDF(7)

CMAC and KMAC
See "Supported parameters" in EVP_MAC-CMAC(7) and "Supported parameters" in EVP_MAC-KMAC(7)

The following FIPS algorithms are unapproved and use the "fips-indicator".

RAND-TEST-RAND
See "Supported parameters" in EVP_RAND-TEST-RAND(7) The indicator callback is NOT triggered for this
algorithm since it is used internally for non security purposes.

X25519 and X448 Key Generation and Key Exchange

The unapproved (non FIPS validated) algorithms have a property query value of "fips=no".

The following algorithms use a unique indicator and do not trigger the indicator callback.

AES-GCM ciphers support the indicator "iv-generated"
See "PARAMETERS" in EVP_EncryptInit(3) for further information.

ECDSA and RSA Signatures support the indicator "verify-message".
See "ECDSA Signature Parameters" in EVP_SIGNATURE-ECDSA(7) and "Signature Parameters" in
EVP_SIGNATURE-RSA(7) /for further information.

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.

       As  the  FIPS  provider  still  supports  non-FIPS validated algorithms, The property query "fips=yes" is
       mandatory for applications that want to operate in a FIPS approved manner.

HISTORY

       The FIPS module guide was created for use with the new FIPS provider in  OpenSSL  3.0.   FIPS  indicators
       were added in OpenSSL 3.4.

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