# OpenSSH /etc/ssh/sshd_config. I am removing commented lines for this to
# be more clear and if they are missed some day, just download
# upstream config file or take it from any distribution.

# Partially based on https://wiki.mozilla.org/Security/Guidelines/OpenSSH
# where some comments are took. Some options look like I don't want to
# change them to get updates when defaults change.

# Allow the client to send needed environment variables. I don't like
# setting wildcards and LC_ALL is disabled on purpouse.
AcceptEnv EDITOR LANG LANGUAGE LC_CTYPE LC_NUMERIC LC_TIME LC_COLLATE LC_MONETARY LC_MESSAGES LC_PAPER LC_NAME LC_ADDRESS LC_TELEPHONE LC_MEASUREMENT LC_IDENTIFICATION TERM TZ

# IPv4 & IPv6
AddressFamily any

# Password based logins are disabled - only public key based logins are
# allowed.
AuthenticationMethods publickey

# The default is to check both .ssh/authorized_keys and
# .ssh/authorized_keys2 but this is overridden so installations will only
# check .ssh/authorized_keys.
AuthorizedKeysFile  .ssh/authorized_keys

# File to send to client before authentication.
Banner /etc/issue.net

# Disable s/key passwords.
ChallengeResponseAuthentication no

# If the client doesn't reply in three "pings", connection is dead.
# Defaults to 3 anyway, but I add it here for clearity and
# in case it decides to change in the future.
ClientAliveCountMax 3

# "ping" the client every minute.
ClientAliveInterval 60

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

## IF THE HOST KEYS ARE MISSING, RUN THE FOLLOWING AS ROOT:
# ssh-keygen -t ed25519 -N "" -f /etc/ssh/ssh_host_ed25519_key
# ssh-keygen -t rsa -N "" -f /etc/ssh/ssh_host_rsa_key

# Listen on the following TCP ports, default 22.
# /etc/ssh/sshd_config ...: ports must be specified before ListenAddress.
Port 22

# Listen on all IPv4 & IPv6 addresses.
ListenAddress 0.0.0.0
ListenAddress ::

# Use the internal SFTP to avoid having to find the external one. VERBOSE
# logs transactions that sftp-server performs on behalf of the client.
# See also http://serverfault.com/a/660325
Subsystem sftp internal-sftp -l VERBOSE
# If you wish to use the external one, uncomment the appropiate one
# for your OS or find it somewhere.
## Arch
#Subsystem   sftp    /usr/lib/ssh/sftp-server -l VERBOSE
## Debian
#Subsystem sftp /usr/lib/openssh/sftp-server -l VERBOSE
## Fedora (21)
#Subsystem sftp /usr/libexec/openssh/sftp-server -l VERBOSE
## Gentoo (/usr/lib is a symlink)
#Subsystem sftp /usr/lib/misc/sftp-server -l VERBOSE

# VERBOSE logging, logs user's key fingerprint on login. Needed to have a
# clear audit track of which key was using to log in.
LogLevel VERBOSE

# Disable tunneled clear text passwords!
PasswordAuthentication no

# Auditing reasons, difficult to track which process belongs to which root
# user.
PermitRootLogin no

# Print /etc/motd (or /etc/profile or equivalent) on login. It's already
# done by PAM, so no need for duplicate MOTDs.
PrintMotd no

# Avoid enabling insecure protocol 1.
Protocol 2

# 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 yes

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