#!/bin/bash
#
# .---.                  .              .
# |                      |              |
# |--- .--. .-.  .-.  .-.|  .-. .--.--. |.-.  .-. .--.  .-.
# |    |   (.-' (.-' (   | (   )|  |  | |   )(   )|  | (.-'
# '    '     --'  --'  -' -  -' '  '   -' -'   -' '   -  --'
#
#                    Freedom in the Cloud
#
# ssh functions
#
# License
# =======
#
# Copyright (C) 2014-2016 Bob Mottram <bob@robotics.uk.to>
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU Affero General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU Affero General Public License for more details.
#
# You should have received a copy of the GNU Affero General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.

SSH_PORT=2222

# Settings from bettercrypto.org
SSH_CIPHERS="aes256-gcm@openssh.com,aes128-gcm@openssh.com,aes256-ctr,aes128-ctr"
SSH_MACS="hmac-sha2-512-etm@openssh.com,hmac-sha2-256-etm@openssh.com,umac-128-etm@openssh.com,hmac-sha2-512,hmac-sha2-256,hmac-ripemd160"
SSH_KEX="diffie-hellman-group-exchange-sha256,diffie-hellman-group14-sha1,diffie-hellman-group-exchange-sha1"
SSH_HOST_KEY_ALGORITHMS="ssh-ed25519-cert-v01@openssh.com,ssh-rsa-cert-v01@openssh.com,ssh-rsa-cert-v00@openssh.com,ssh-ed25519,ssh-rsa"

function configure_ssh {
    if [[ $(is_completed $FUNCNAME) == "1" ]]; then
        return
    fi
    sed -i "s/Port .*/Port $SSH_PORT/g" /etc/ssh/sshd_config
    sed -i 's/PermitRootLogin.*/PermitRootLogin no/g' /etc/ssh/sshd_config
    sed -i 's/X11Forwarding.*/X11Forwarding no/g' /etc/ssh/sshd_config
    sed -i 's/ServerKeyBits.*/ServerKeyBits 4096/g' /etc/ssh/sshd_config
    sed -i 's/TCPKeepAlive.*/TCPKeepAlive no/g' /etc/ssh/sshd_config
    sed -i 's|HostKey /etc/ssh/ssh_host_dsa_key|#HostKey /etc/ssh/ssh_host_dsa_key|g' /etc/ssh/sshd_config
    sed -i 's|HostKey /etc/ssh/ssh_host_ecdsa_key|#HostKey /etc/ssh/ssh_host_ecdsa_key|g' /etc/ssh/sshd_config
    if ! grep -q 'DebianBanner' /etc/ssh/sshd_config; then
        echo 'DebianBanner no' >> /etc/ssh/sshd_config
    else
        sed -i 's|DebianBanner.*|DebianBanner no|g' /etc/ssh/sshd_config
    fi
    if grep -q 'ClientAliveInterval' /etc/ssh/sshd_config; then
        sed -i 's/ClientAliveInterval.*/ClientAliveInterval 60/g' /etc/ssh/sshd_config
    else
        echo 'ClientAliveInterval 60' >> /etc/ssh/sshd_config
    fi
    if grep -q 'ClientAliveCountMax' /etc/ssh/sshd_config; then
        sed -i 's/ClientAliveCountMax.*/ClientAliveCountMax 3/g' /etc/ssh/sshd_config
    else
        echo 'ClientAliveCountMax 3' >> /etc/ssh/sshd_config
    fi
    if grep -q 'Ciphers' /etc/ssh/sshd_config; then
        sed -i "s|Ciphers.*|Ciphers $SSH_CIPHERS|g" /etc/ssh/sshd_config
    else
        echo "Ciphers $SSH_CIPHERS" >> /etc/ssh/sshd_config
    fi
    if grep -q 'MACs' /etc/ssh/sshd_config; then
        sed -i "s|MACs.*|MACs $SSH_MACS|g" /etc/ssh/sshd_config
    else
        echo "MACs $SSH_MACS" >> /etc/ssh/sshd_config
    fi
    if grep -q 'KexAlgorithms' /etc/ssh/sshd_config; then
        sed -i "s|KexAlgorithms.*|KexAlgorithms $SSH_KEX|g" /etc/ssh/sshd_config
    else
        echo "KexAlgorithms $SSH_KEX" >> /etc/ssh/sshd_config
    fi

    apt-get -y install fail2ban

    function_check configure_firewall_for_ssh
    configure_firewall_for_ssh
    mark_completed $FUNCNAME
}

# see https://stribika.github.io/2015/01/04/secure-secure-shell.html
function ssh_remove_small_moduli {
    awk '$5 > 2000' /etc/ssh/moduli > ~/moduli
    mv ~/moduli /etc/ssh/moduli
}

function configure_ssh_client {
    if [[ $(is_completed $FUNCNAME) == "1" ]]; then
        return
    fi
    #sed -i 's/#   PasswordAuthentication.*/   PasswordAuthentication no/g' /etc/ssh/ssh_config
    #sed -i 's/#   ChallengeResponseAuthentication.*/   ChallengeResponseAuthentication no/g' /etc/ssh/ssh_config
    sed -i "s/#   HostKeyAlgorithms.*/   HostKeyAlgorithms $SSH_HOST_KEY_ALGORITHMS/g" /etc/ssh/ssh_config
    sed -i "s/#   Ciphers.*/   Ciphers $SSH_CIPHERS/g" /etc/ssh/ssh_config
    sed -i "s/#   MACs.*/   MACs $SSH_MACS/g" /etc/ssh/ssh_config
    if ! grep -q "HostKeyAlgorithms" /etc/ssh/ssh_config; then
        echo "   HostKeyAlgorithms $SSH_HOST_KEY_ALGORITHMS" >> /etc/ssh/ssh_config
    fi
    sed -i "s/Ciphers.*/Ciphers $SSH_CIPHERS/g" /etc/ssh/ssh_config
    if ! grep -q "Ciphers " /etc/ssh/ssh_config; then
        echo "   Ciphers $SSH_CIPHERS" >> /etc/ssh/ssh_config
    fi
    sed -i "s/MACs.*/MACs $SSH_MACS/g" /etc/ssh/ssh_config
    if ! grep -q "MACs " /etc/ssh/ssh_config; then
        echo "   MACs $SSH_MACS" >> /etc/ssh/ssh_config
    fi

    # Create ssh keys
    if [ ! -f ~/.ssh/id_ed25519 ]; then
        ssh-keygen -t ed25519 -o -a 100
    fi
    if [ ! -f ~/.ssh/id_rsa ]; then
        ssh-keygen -t rsa -b 4096 -o -a 100
    fi

    function_check ssh_remove_small_moduli
    ssh_remove_small_moduli
    mark_completed $FUNCNAME
}

function regenerate_ssh_keys {
    if [[ $(is_completed $FUNCNAME) == "1" ]]; then
        return
    fi
    rm -f /etc/ssh/ssh_host_*
    dpkg-reconfigure openssh-server

    function_check ssh_remove_small_moduli
    ssh_remove_small_moduli

    systemctl restart ssh
    mark_completed $FUNCNAME
}

# NOTE: deliberately no exit 0