Linux-Setup-Scripts/etc/ssh/sshd_config.d/10-custom.conf

# Encryption hardening
HostKey /etc/ssh/ssh_host_ed25519_key
HostKeyAlgorithms ssh-ed25519
KexAlgorithms sntrup761x25519-sha512@openssh.com
PubkeyAcceptedKeyTypes ssh-ed25519
Ciphers aes256-gcm@openssh.com
MACs -*

# Security hardening
AuthenticationMethods publickey
AuthorizedKeysFile .ssh/authorized_keys
Compression no
DisableForwarding yes
LoginGraceTime 15s
MaxAuthTries 1
PermitUserEnvironment no
PermitUserRC no
StrictModes yes
UseDNS no

# Use KeepAlive over SSH instead of with TCP to prevent spoofing
TCPKeepAlive no
ClientAliveInterval 15
ClientAliveCountMax 4

## Use PAM for session checks here but authentication is disabled below
## Also, this prevents running sshd as non-root
UsePAM yes

# Disabling unused authentication methods
ChallengeResponseAuthentication no
GSSAPIAuthentication no
HostbasedAuthentication no
PasswordAuthentication no
PermitRootLogin no
PermitEmptyPasswords no
KbdInteractiveAuthentication no
KerberosAuthentication no

# Displaying info
Banner /etc/issue.net
PrintLastLog yes
PrintMotd yes