Chapter 3. Using system-wide cryptographic policies

When a system-wide policy is set up, applications in RHEL follow it and refuse to use algorithms and protocols that do not meet the policy, unless you explicitly request the application to do so. That is, the policy applies to the default behavior of applications when running with the system-provided configuration but you can override it if required.

RHEL 9 contains the following predefined policies:

Red Hat continuously adjusts all policy levels so that all libraries provide secure defaults, except when using the LEGACY policy. Even though the LEGACY profile does not provide secure defaults, it does not include any algorithms that are easily exploitable. As such, the set of enabled algorithms or acceptable key sizes in any provided policy may change during the lifetime of Red Hat Enterprise Linux.

Such changes reflect new security standards and new security research. If you must ensure interoperability with a specific system for the whole lifetime of Red Hat Enterprise Linux, you should opt-out from the system-wide cryptographic policies for components that interact with that system or re-enable specific algorithms using custom cryptographic policies.

Tool for managing the cryptographic policies

To view or change the current system-wide cryptographic policy, use the update-crypto-policies tool, for example:

$ update-crypto-policies --show
DEFAULT
# update-crypto-policies --set FUTURE
Setting system policy to FUTURE

To ensure that the change of the cryptographic policy is applied, restart the system.

Strong cryptographic defaults by removing insecure cipher suites and protocols

The following list contains cipher suites and protocols removed from the core cryptographic libraries in RHEL. Because they are not present in the sources, or their support is disabled during the build, applications cannot use them.

Algorithms disabled in all policy levels

The following algorithms are disabled in LEGACY, DEFAULT, FUTURE, and FIPS cryptographic policies included in RHEL 9. They can be enabled only by applying a custom cryptographic policy or by an explicit configuration of individual applications, but the resulting configuration falls outside of the Production Support Scope of Coverage.

Algorithms enabled in the cryptographic policies

Each cryptographic policy enables specific cipher suites and protocols:

The default system-wide cryptographic policy in Red Hat Enterprise Linux 9 does not allow communication using older, insecure protocols. For environments that require to be compatible with Red Hat Enterprise Linux 6 and in some cases also with earlier releases, the less secure LEGACY policy level is available.

You can set one of system-wide cryptographic policies and subpolicies directly in the RHEL web console interface. Besides the four predefined system-wide cryptographic policies, you can also apply the following combinations of policies and subpolicies through the graphical interface now:

The system-wide cryptographic policies contain a policy level that enables cryptographic algorithms in accordance with the requirements by the Federal Information Processing Standard (FIPS) Publication 140. The fips-mode-setup tool that enables or disables FIPS mode internally uses the FIPS system-wide cryptographic policy.

Switching the system to FIPS mode by using the FIPS system-wide cryptographic policy does not guarantee compliance with the FIPS 140 standard. Re-generating all cryptographic keys after setting the system to FIPS mode may not be possible. For example, in the case of an existing IdM realm with users' cryptographic keys you cannot re-generate all the keys.

The fips-mode-setup tool uses the FIPS policy internally. But on top of what the update-crypto-policies command with the --set FIPS option does, fips-mode-setup ensures the installation of the FIPS dracut module by using the fips-finish-install tool, it also adds the fips=1 boot option to the kernel command line and regenerates the initial RAM disk.

To enable the full set of cryptographic module self-checks mandated by the Federal Information Processing Standard Publication 140-2 (FIPS mode), the host system kernel must be running in FIPS mode. The podman utility automatically enables FIPS mode on supported containers.

To pass all relevant cryptographic certifications, such as FIPS 140-3, use libraries from the core cryptographic components set. These libraries, except from libgcrypt, also follow the RHEL system-wide cryptographic policies.

See the RHEL core cryptographic components article for an overview of the core cryptographic components, the information on how are they selected, how are they integrated into the operating system, how do they support hardware security modules and smart cards, and how do cryptographic certifications apply to them.

You can customize cryptographic settings used by your application preferably by configuring supported cipher suites and protocols directly in the application.

You can also remove a symlink related to your application from the /etc/crypto-policies/back-ends directory and replace it with your customized cryptographic settings. This configuration prevents the use of system-wide cryptographic policies for applications that use the excluded back end. Furthermore, this modification is not supported by Red Hat.

$ wget --secure-protocol=TLSv1_1 --ciphers="SECURE128" https://example.com

$ curl https://example.com --ciphers '@SECLEVEL=0:DES-CBC3-SHA:RSA-DES-CBC3-SHA'

Use this procedure to adjust the set of enabled cryptographic algorithms or protocols.

You can either apply custom subpolicies on top of an existing system-wide cryptographic policy or define such a policy from scratch.

The concept of scoped policies allows enabling different sets of algorithms for different back ends. You can limit each configuration directive to specific protocols, libraries, or services.

Furthermore, directives can use asterisks for specifying multiple values using wildcards.

The /etc/crypto-policies/state/CURRENT.pol file lists all settings in the currently applied system-wide cryptographic policy after wildcard expansion. To make your cryptographic policy more strict, consider using values listed in the /usr/share/crypto-policies/policies/FUTURE.pol file.

You can find example subpolicies in the /usr/share/crypto-policies/policies/modules/ directory. The subpolicy files in this directory contain also descriptions in lines that are commented out.

The use of the SHA-1 algorithm for creating and verifying signatures is restricted in the DEFAULT cryptographic policy. If your scenario requires the use of SHA-1 for verifying existing or third-party cryptographic signatures, you can enable it by applying the SHA1 subpolicy, which RHEL 9 provides by default. Note that it weakens the security of the system.

The following steps demonstrate customizing the system-wide cryptographic policies by a complete policy file.