Chapter 3. Using system-wide cryptographic policies

Crypto policies is a system component that configures the core cryptographic subsystems, covering the TLS, IPSec, SSH, DNSSec, and Kerberos protocols. It provides a small set of policies, which the administrator can select.

3.1. System-wide cryptographic policies

Once 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 so.

Red Hat Enterprise Linux 8 contains the following policy levels:

DEFAULT

The default system-wide cryptographic policy level offers secure settings for current threat models. It allows the TLS 1.2 and 1.3 protocols, as well as the IKEv2 and SSH2 protocols. The RSA keys and Diffie-Hellman parameters are accepted if they are at least 2048 bits long.

LEGACY

This policy ensures maximum compatibility with Red Hat Enterprise Linux 5 and earlier; it is less secure due to an increased attack surface. In addition to the DEFAULT level algorithms and protocols, it includes support for the TLS 1.0 and 1.1 protocols. The algorithms DSA, 3DES, and RC4 are allowed, while RSA keys and Diffie-Hellman parameters are accepted if they are at least 1023 bits long.

FUTURE

A conservative security level that is believed to withstand any near-term future attacks. This level does not allow the use of SHA-1 in signature algorithms. The RSA keys and Diffie-Hellman parameters are accepted if they are at least 3072 bits long.

FIPS

A policy level that conforms with the FIPS140-2 requirements. This is used internally by the fips-mode-setup tool, which switches the RHEL system into FIPS mode.

Note

The specific algorithms and ciphers described in the policy levels as allowed are available only if an application supports them.

Tool for managing crypto 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 crypto defaults by removing insecure cipher suites and protocols

The following list contains cipher suites and protocols removed from the core cryptographic libraries in RHEL 8. They are not present in the sources, or their support is disabled during the build, so applications cannot use them.

  • DES (since RHEL 7)
  • All export grade cipher suites (since RHEL 7)
  • MD5 in signatures (since RHEL 7)
  • SSLv2 (since RHEL 7)
  • SSLv3 (since RHEL 8)
  • All ECC curves < 224 bits (since RHEL 6)
  • All binary field ECC curves (since RHEL 6)

Cipher suites and protocols disabled in all policy levels

The following cipher suites and protocols are disabled in all crypto policy levels. They can be enabled only by an explicit configuration of individual applications.

  • DH with parameters < 1024 bits
  • RSA with key size < 1024 bits
  • Camellia
  • ARIA
  • SEED
  • IDEA
  • Integrity-only cipher suites
  • TLS CBC mode cipher suites using SHA-384 HMAC
  • AES-CCM8
  • All ECC curves incompatible with TLS 1.3, including secp256k1
  • IKEv1 (since RHEL 8)

Cipher suites and protocols enabled in the crypto-policies levels

The following table shows the enabled cipher suites and protocols in all four crypto-policies levels.

 LEGACYDEFAULTFIPSFUTURE

IKEv1

no

no

no

no

3DES

yes

no

no

no

RC4

yes

no

no

no

DH

min. 1024-bit

min. 2048-bit

min. 2048-bit

min. 3072-bit

RSA

min. 1024-bit

min. 2048-bit

min. 2048-bit

min. 3072-bit

DSA

yes

no

no

no

TLS v1.0

yes

no

no

no

TLS v1.1

yes

no

no

no

SHA-1 in digital signatures

yes

yes

no

no

CBC mode ciphers

yes

yes

yes

no

Symmetric ciphers with keys < 256 bits

yes

yes

yes

no

SHA-1 and SHA-224 signatures in certificates

yes

yes

yes

no

Additional resources

  • For more details, see the update-crypto-policies(8) man page.

3.2. Switching the system-wide cryptographic policy to mode compatible with earlier releases

The default system-wide cryptographic policy in Red Hat Enterprise Linux 8 does not allow communication using older, insecure protocols. For environments that require to be compatible with Red Hat Enterprise Linux 5 and in some cases also with earlier releases, the less secure LEGACY policy level is available.

Warning

Switching to the LEGACY policy level results in a less secure system and applications.

Procedure

  1. To switch the system-wide cryptographic policy to the LEGACY level, enter the following command as root: 

    # update-crypto-policies --set LEGACY
Setting system policy to LEGACY

Additional resources

  • For the list of available cryptographic policy levels, see the update-crypto-policies(8) man page.

3.3. Switching the system to FIPS mode

The system-wide cryptographic policies contain a policy level that enables cryptographic modules self-checks in accordance with the requirements by Federal Information Processing Standard (FIPS) Publication 140-2. The fips-mode-setup tool that enables or disables FIPS mode internally uses the FIPS system-wide cryptographic policy level.

Procedure

  1. To switch the system to FIPS mode in RHEL 8: 

    # fips-mode-setup --enable
Setting system policy to FIPS
FIPS mode will be enabled.
Please reboot the system for the setting to take effect.

  2. Restart your system to allow the kernel to switch to FIPS mode: 

    # reboot

  3. After the restart, you can check the current state of FIPS mode: 

    # fips-mode-setup --check
FIPS mode is enabled.

Additional resources

3.4. Excluding an application from following system-wide crypto policies

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.

3.4.1. Examples of opting out of system-wide crypto policies

wget

To customize cryptographic settings used by the wget network downloader, use --secure-protocol and --ciphers options. For example: 

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

See the HTTPS (SSL/TLS) Options section of the wget(1) man page for more information.

curl

To specify ciphers used by the curl tool, use the --ciphers option and provide a colon-separated list of ciphers as a value. For example: 

# curl https://example.com --ciphers DES-CBC3-SHA:RSA-DES-CBC3-SHA

See the curl(1) man page for more information.

Firefox

Even though you cannot opt out of system-wide cryptographic policies in the Firefox web browser, you can further restrict supported ciphers and TLS versions in Firefox’s Configuration Editor. Type about:config in the address bar and change the value of the security.tls.version.min option as required. Setting security.tls.version.min to 1 allows TLS 1.0 as the minimum required, security.tls.version.min 2 enables TLS 1.1, and so on.

OpenSSH

To opt out of the system-wide crypto policies for your OpenSSH server, uncomment the line with the CRYPTO_POLICY= variable in the /etc/sysconfig/sshd file. After this change, values that you specify in the Ciphers, MACs, KexAlgoritms, and GSSAPIKexAlgorithms sections in the /etc/ssh/sshd_config file are not overriden. See the sshd_config(5) man page for more information.

Libreswan

To allow the Libreswan IPsec suite to use the IKEv1 protocol, comment out the following line in the /etc/ipsec.conf file: 

include /etc/crypto-policies/back-ends/libreswan.config

Then add the ikev2=never option to your connection configuration. See the ipsec.conf(5) man page for more information.

Additional resources

  • For more details, see the update-crypto-policies(8) man page.