3.8. Customizing system-wide cryptographic policies with subpolicies

Procédure

1. Checkout to the /etc/crypto-policies/policies/modules/ directory:

   # cd /etc/crypto-policies/policies/modules/

2. Create subpolicies for your adjustments, for example:

   # touch MYCRYPTO-1.pmod
   # touch SCOPES-AND-WILDCARDS.pmod

   Important

   Use upper-case letters in file names of policy modules.

3. Open the policy modules in a text editor of your choice and insert options that modify the system-wide cryptographic policy, for example:

   # vi MYCRYPTO-1.pmod

   min_rsa_size = 3072
   hash = SHA2-384 SHA2-512 SHA3-384 SHA3-512

   # vi SCOPES-AND-WILDCARDS.pmod

   # Disable the AES-128 cipher, all modes
   cipher = -AES-128-*
   
   # Disable CHACHA20-POLY1305 for the TLS protocol (OpenSSL, GnuTLS, NSS, and OpenJDK)
   cipher@TLS = -CHACHA20-POLY1305
   
   # Allow using the FFDHE-1024 group with the SSH protocol (libssh and OpenSSH)
   group@SSH = FFDHE-1024+
   
   # Disable all CBC mode ciphers for the SSH protocol (libssh and OpenSSH)
   cipher@SSH = -*-CBC
   
   # Allow the AES-256-CBC cipher in applications using libssh
   cipher@libssh = AES-256-CBC+

4. Save the changes in the module files.

5. Apply your policy adjustments to the DEFAULT system-wide cryptographic policy level:

   # update-crypto-policies --set DEFAULT:MYCRYPTO-1:SCOPES-AND-WILDCARDS

6. To make your cryptographic settings effective for already running services and applications, restart the system:

   # reboot