Secure SSH Config

ssh_config

# Recommendations from https://stribika.github.io/2015/01/04/secure-secure-shell.html

# Github needs diffie-hellman-group-exchange-sha1 some of the time but not always.
#Host github.com
#    KexAlgorithms curve25519-sha256@libssh.org,diffie-hellman-group-exchange-sha256,diffie-hellman-group-exchange-sha1,diffie-hellman-group14-sha1

Host *
    KexAlgorithms curve25519-sha256@libssh.org,diffie-hellman-group-exchange-sha256

Host *
    PasswordAuthentication no
    ChallengeResponseAuthentication no

Host *
    PubkeyAuthentication yes
    HostKeyAlgorithms ssh-ed25519-cert-v01@openssh.com,ssh-rsa-cert-v01@openssh.com,ssh-ed25519,ssh-rsa

Host *
    Ciphers chacha20-poly1305@openssh.com,aes256-gcm@openssh.com,aes128-gcm@openssh.com,aes256-ctr,aes192-ctr,aes128-ctr

Host *
    MACs hmac-sha2-512-etm@openssh.com,hmac-sha2-256-etm@openssh.com,hmac-ripemd160-etm@openssh.com,umac-128-etm@openssh.com,hmac-sha2-512,hmac-sha2-256,hmac-ripemd160,umac-128@openssh.com

Host *
   UseRoaming no

sshd_config

# Recommendations from https://stribika.github.io/2015/01/04/secure-secure-shell.html

KexAlgorithms curve25519-sha256@libssh.org,diffie-hellman-group-exchange-sha256

Protocol 2
HostKey /etc/ssh/ssh_host_rsa_key
HostKey /etc/ssh/ssh_host_ed25519_key

PasswordAuthentication no
ChallengeResponseAuthentication no

PubkeyAuthentication yes

# Unpractical for the forge user in case of reprovision?
# AllowGroups ssh-user

Ciphers chacha20-poly1305@openssh.com,aes256-gcm@openssh.com,aes128-gcm@openssh.com,aes256-ctr,aes192-ctr,aes128-ctr

MACs hmac-sha2-512-etm@openssh.com,hmac-sha2-256-etm@openssh.com,hmac-ripemd160-etm@openssh.com,umac-128-etm@openssh.com,hmac-sha2-512,hmac-sha2-256,hmac-ripemd160,umac-128@openssh.com