NixOS must implement DOD-approved encryption to protect the confidentiality of remote access sessions.

Without confidentiality protection mechanisms, unauthorized individuals may gain access to sensitive information via a remote access session.

Remote access is access to DOD nonpublic information systems by an authorized user (or an information system) communicating through an external, nonorganization-controlled network. Remote access methods include, for example, dial-up, broadband, and wireless.

Encryption provides a means to secure the remote connection to prevent unauthorized access to the data traversing the remote access connection (e.g., RDP), thereby providing a degree of confidentiality. The encryption strength of a mechanism is selected based on the security categorization of the information.

Satisfies: SRG-OS-000033-GPOS-00014, SRG-OS-000250-GPOS-00093, SRG-OS-000394-GPOS-00174

Verify NixOS is configured to only use ciphers employing FIPS 140-3 approved algorithms with the following command:

$ grep Ciphers /etc/ssh/sshd_config Ciphers aes256-ctr,aes192-ctr,aes128-ctr

If the cipher entries in the "sshd_config" file have any ciphers other than "aes256-ctr,aes192-ctr,aes128-ctr", the order differs from the example above, or they are missing or commented out, this is a finding.

Configure NixOS to use only ciphers employing FIPS 140-3 approved algorithms.

To configure OpenSSH, add the following Nix code to the NixOS Configuration, usually located in /etc/nixos/configuration.nix or /etc/nixos/flake.nix:

services.openssh.setting.Ciphers = [ "aes256-ctr" "aes192-ctr" "aes128-ctr" ];

Rebuild and switch to the new NixOS configuration: $ sudo nixos-rebuild switch