Hardened SSH Server Config 03/2016

sshd_config

# TCP port to bind to
# Change to a high/odd port if this server is exposed to the internet directly
Port 22

# Bind to all interfaces (change to specific interface if needed)
ListenAddress 0.0.0.0

# Force SSHv2 Protocol
Protocol 2

# HostKeys for protocol version 2
HostKey /etc/ssh/ssh_host_rsa_key
HostKey /etc/ssh/ssh_host_dsa_key
HostKey /etc/ssh/ssh_host_ecdsa_key

# Use kernel sandbox mechanisms where possible in unprivileged processes
# Systrace on OpenBSD, Seccomp on Linux, seatbelt on MacOSX/Darwin, rlimit elsewhere.
UsePrivilegeSeparation sandbox

# Deny all other users besides the following
AllowUsers tristor

# Client timeout (5 minutes)
ClientAliveInterval 300
ClientAliveCountMax 0

# Compression (only after authentication)
Compression delayed

# Logging
SyslogFacility AUTH
LogLevel INFO

# Authentication must happen within 30 seconds
LoginGraceTime 30

# Disable root SSH access
PermitRootLogin no
PermitEmptyPasswords no

# Check user folder permissions before allowing access
StrictModes yes

# Public key authentication + Password authentication
# Two-Factor Authentication in OpenSSH v6.2+
RSAAuthentication yes
PubkeyAuthentication yes
PasswordAuthentication yes
AuthenticationMethods publickey,password

# Change this depending on where your authorized_keys file is
# This is set as a workaround when using encrypted home directories
# Link: https://joscor.com/2013/05/putty-server-refused-our-key/
#AuthorizedKeysFile /etc/ssh/keys/%u/authorized_keys

#These are the most secure of the available ciphers and MACs
# SHA-256 included for compat with PuTTY-WinCrypt clients
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,umac-128-etm@openssh.com,hmac-sha2-512,hmac-sha2-256,umac-128@openssh.com

# Key Exchange algorithms (Elliptic Curve Diffie-Hellman)
# DH-SHA-256 included for compat with PuTTY-WinCrypt clients
KexAlgorithms curve25519-sha256@libssh.org,ecdh-sha2-nistp521,ecdh-sha2-nistp384,ecdh-sha2-nistp256,diffie-hellman-group-exchange-sha256

# Don’t read the user’s ~/.rhosts and ~/.shosts files
IgnoreRhosts yes

# Disable unused authentication schemes
RhostsRSAAuthentication no
HostbasedAuthentication no
ChallengeResponseAuthentication no
KerberosAuthentication no
GSSAPIAuthentication no
# This may need to be enabled for things like Google Authenticator/YubiOTP
UsePAM no

# X11 support
X11Forwarding no

# Don’t show Message of the Day
PrintMotd no

# TCPKeepAlive (non-tunneled, disabled)
TCPKeepAlive no

# Allow client to pass locale environment variables
AcceptEnv LANG LC_*

Hey. Maybe you should add more tweaks ;)

PermitUserEnvironment no
# Log sftp level file access (read/write/etc.) that would not be easily logged otherwise.
Subsystem sftp internal-sftp -f AUTHPRIV -l INFO
AllowTcpForwarding no
AllowStreamLocalForwarding no
GatewayPorts no
PermitTunnel no
UseDNS no
Compression no
AllowAgentForwarding no
MaxAuthTries 2
MaxSessions 2
MaxStartups 2
DebianBanner no
ChallengeResponseAuthentication no