SSHD configuration

00-wiki-sshd.md

This is my standard SSH setup based on stribika.github.io.

1. Secure moduli

awk '$5 > 2000' /etc/ssh/moduli > "$HOME/moduli"
# Make sure there is something left
wc -l "$HOME/moduli"
mv /etc/ssh/moduli /etc/ssh/moduli.bak
mv "$HOME/moduli" /etc/ssh/moduli

When there are no moduli with a keysize > 2000 you should gereate a new set:

ssh-keygen -G /etc/ssh/moduli.all -b 4096
ssh-keygen -T /etc/ssh/moduli.safe -f /etc/ssh/moduli.all
mv /etc/ssh/moduli.safe /etc/ssh/moduli
rm /etc/ssh/moduli.all

Remove default ssh_host_keys and gererate a new pair:

rm /etc/ssh/ssh_host_*key*
ssh-keygen -t ed25519 -f /etc/ssh/ssh_host_ed25519_key < /dev/null
ssh-keygen -t rsa -b 4096 -f /etc/ssh/ssh_host_rsa_key < /dev/null

Backup default configuration and copy mine:

mv /etc/ssh/ssh_config /etc/ssh/ssh_config.orig
mv /etc/ssh/sshd_config /etc/ssh/sshd_config.orig
cp $HOME/<git_repo>/ss{h,hd}_config /etc/ssh

INSTALL

#!/bin/bash
awk '$5 > 2000' /etc/ssh/moduli > "$HOME/moduli"
if if [[ -z $(wc -l "$HOME/moduli") ]]; then
  echo "No sufficient DH moduli found, please refer to README.md on how to gereate a good set of moduli."
  exit 33
else
  echo "Successfully secured your DH moduli (min. 2048bit)"
  mv /etc/ssh/moduli /etc/ssh/moduli.bak
  mv "$HOME/moduli" /etc/ssh/moduli
fi
rm /etc/ssh/ssh_host_*key*
ssh-keygen -t ed25519 -f /etc/ssh/ssh_host_ed25519_key < /dev/null
ssh-keygen -t rsa -b 4096 -f /etc/ssh/ssh_host_rsa_key < /dev/null
mv /etc/ssh/ssh_config /etc/ssh/ssh_config.orig
mv /etc/ssh/sshd_config /etc/ssh/sshd_config.orig
echo "Please copy ss{h,hd}_config to /etc/ssh/"
echo "Also make sure to copy your public key into $HOME/.ssh/authorized_keys !!"
exit 1

ssh_config

#	$OpenBSD: ssh_config,v 1.28 2013/09/16 11:35:43 sthen Exp $

# This is the ssh client system-wide configuration file.  See
# ssh_config(5) for more information.  This file provides defaults for
# users, and the values can be changed in per-user configuration files
# or on the command line.

# Configuration data is parsed as follows:
#  1. command line options
#  2. user-specific file
#  3. system-wide file
# Any configuration value is only changed the first time it is set.
# Thus, host-specific definitions should be at the beginning of the
# configuration file, and defaults at the end.

# Site-wide defaults for some commonly used options.  For a comprehensive
# list of available options, their meanings and defaults, please see the
# ssh_config(5) man page.

Host *
	PubkeyAuthentication yes
	ForwardX11 yes
	KexAlgorithms curve25519-sha256@libssh.org,diffie-hellman-group-exchange-sha256
	HostKeyAlgorithms ssh-ed25519-cert-v01@openssh.com,ssh-rsa-cert-v01@openssh.com,ssh-ed25519,ssh-rsa
	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
	UseRoaming no

sshd_config

# Package generated configuration file
# See the sshd_config(5) manpage for details

# What ports, IPs and protocols we listen for
Port 22
# Use these options to restrict which interfaces/protocols sshd will bind to
#ListenAddress ::
#ListenAddress 0.0.0.0
Protocol 2

# HostKeys for protocol version 2
HostKey /etc/ssh/ssh_host_ed25519_key
HostKey /etc/ssh/ssh_host_rsa_key
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

# SSH hardening, see https://stribika.github.io/2015/01/04/secure-secure-shell.html
KexAlgorithms curve25519-sha256@libssh.org,diffie-hellman-group-exchange-sha256

#Privilege Separation is turned on for security
UsePrivilegeSeparation yes

# Lifetime and size of ephemeral version 1 server key
KeyRegenerationInterval 3600
ServerKeyBits 1024

# Logging
SyslogFacility AUTH
LogLevel INFO

# Authentication:
LoginGraceTime 120
PermitRootLogin prohibit-password
StrictModes yes

RSAAuthentication yes
PubkeyAuthentication yes
AuthorizedKeysFile      %h/.ssh/authorized_keys

# Don't read the user's ~/.rhosts and ~/.shosts files
IgnoreRhosts yes
# For this to work you will also need host keys in /etc/ssh_known_hosts
RhostsRSAAuthentication no
# similar for protocol version 2
HostbasedAuthentication no
# Uncomment if you don't trust ~/.ssh/known_hosts for RhostsRSAAuthentication
#IgnoreUserKnownHosts yes

# To enable empty passwords, change to yes (NOT RECOMMENDED)
PermitEmptyPasswords no

# Change to yes to enable challenge-response passwords (beware issues with
# some PAM modules and threads)
ChallengeResponseAuthentication no

# Change to no to disable tunnelled clear text passwords
PasswordAuthentication no

# Kerberos options
#KerberosAuthentication no
#KerberosGetAFSToken no
#KerberosOrLocalPasswd yes
#KerberosTicketCleanup yes

# GSSAPI options
#GSSAPIAuthentication no
#GSSAPICleanupCredentials yes

X11Forwarding yes
X11DisplayOffset 10
PrintMotd no
PrintLastLog yes
TCPKeepAlive yes
#UseLogin no

#MaxStartups 10:30:60
#Banner /etc/issue.net

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

Subsystem sftp /usr/lib/openssh/sftp-server

# Set this to 'yes' to enable PAM authentication, account processing,
# and session processing. If this is enabled, PAM authentication will
# be allowed through the ChallengeResponseAuthentication and
# PasswordAuthentication.  Depending on your PAM configuration,
# PAM authentication via ChallengeResponseAuthentication may bypass
# the setting of "PermitRootLogin without-password".
# If you just want the PAM account and session checks to run without
# PAM authentication, then enable this but set PasswordAuthentication
# and ChallengeResponseAuthentication to 'no'.
UsePAM no