Tested against:

• Red Hat Enterprise Linux (RHEL) 10.1
• Fedora 43

Server

printf "KexAlgorithms mlkem768x25519-sha256,sntrup761x25519-sha512,[email protected],curve25519-sha256,[email protected]\nCiphers [email protected],aes256-ctr,aes192-ctr,[email protected],aes128-ctr\nMACs [email protected],[email protected],[email protected]\nHostKeyAlgorithms [email protected],[email protected],[email protected],[email protected],[email protected],ssh-ed25519,rsa-sha2-512,rsa-sha2-256\nCASignatureAlgorithms [email protected],ssh-ed25519,rsa-sha2-512,rsa-sha2-256\nHostbasedAcceptedAlgorithms [email protected],[email protected],[email protected],[email protected],[email protected],ssh-ed25519,rsa-sha2-512,rsa-sha2-256\nPubkeyAcceptedAlgorithms [email protected],[email protected],[email protected],[email protected],[email protected],ssh-ed25519,rsa-sha2-512,rsa-sha2-256\n" | sudo tee /etc/ssh/sshd_config.d/01-hardened-ssh.conf

sudo rm -f /etc/ssh/ssh_host_*
sudo ssh-keygen -t rsa -b 4096 -f /etc/ssh/ssh_host_rsa_key -N ""
sudo ssh-keygen -t ed25519 -f /etc/ssh/ssh_host_ed25519_key -N ""
sudo systemctl restart sshd

Client

mkdir -p -m 0700 ~/.ssh; printf "\nHost *\n  Ciphers [email protected],[email protected],aes256-ctr,aes192-ctr,aes128-ctr\n\n  KexAlgorithms mlkem768x25519-sha256,sntrup761x25519-sha512,[email protected],curve25519-sha256,[email protected],diffie-hellman-group16-sha512,diffie-hellman-group18-sha512,diffie-hellman-group-exchange-sha256\n\n  MACs [email protected],[email protected],[email protected]\n\n  HostKeyAlgorithms [email protected],[email protected],[email protected],[email protected],[email protected],ssh-ed25519,rsa-sha2-512,rsa-sha2-256\n\n  CASignatureAlgorithms [email protected],ssh-ed25519,rsa-sha2-512,rsa-sha2-256\n\n  HostbasedAcceptedAlgorithms [email protected],[email protected],[email protected],ssh-ed25519,[email protected],rsa-sha2-512,[email protected],rsa-sha2-256\n\n  PubkeyAcceptedAlgorithms [email protected],[email protected],[email protected],ssh-ed25519,[email protected],rsa-sha2-512,[email protected],rsa-sha2-256\n" >> ~/.ssh/config