#!/bin/bash
#  _____               _           _
# |   __|___ ___ ___ _| |___ _____| |_ ___ ___ ___
# |   __|  _| -_| -_| . | . |     | . | . |   | -_|
# |__|  |_| |___|___|___|___|_|_|_|___|___|_|_|___|
#
#                              Freedom in the Cloud
#
# ssh functions
#
# License
# =======
#
# Copyright (C) 2014-2018 Bob Mottram <bob@freedombone.net>
#
# 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 openssh 6.6+
SSH_CIPHERS="chacha20-poly1305@openssh.com,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"
SSH_KEX="curve25519-sha256@libssh.org,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[0]}") == "1" ]]; then
        return
    fi

    if ! grep -q 'RhostsRSAAuthentication' /etc/ssh/sshd_config; then
        echo 'RhostsRSAAuthentication yes' >> /etc/ssh/sshd_config
    fi
    sed -i 's|#RhostsRSAAuthentication.*|RhostsRSAAuthentication yes|g' /etc/ssh/sshd_config
    sed -i 's|RhostsRSAAuthentication.*|RhostsRSAAuthentication yes|g' /etc/ssh/sshd_config
    sed -i 's|#StrictModes.*|StrictModes yes|g' /etc/ssh/sshd_config
    sed -i 's|StrictModes.*|StrictModes yes|g' /etc/ssh/sshd_config
    sed -i 's|#KerberosAuthentication.*|KerberosAuthentication no|g' /etc/ssh/sshd_config
    sed -i 's|KerberosAuthentication.*|KerberosAuthentication no|g' /etc/ssh/sshd_config
    sed -i 's|#GSSAPIAuthentication.*|GSSAPIAuthentication no|g' /etc/ssh/sshd_config
    sed -i 's|GSSAPIAuthentication.*|GSSAPIAuthentication no|g' /etc/ssh/sshd_config
    sed -i 's|#IgnoreUserKnownHosts.*|IgnoreUserKnownHosts yes|g' /etc/ssh/sshd_config
    sed -i 's|IgnoreUserKnownHosts.*|IgnoreUserKnownHosts yes|g' /etc/ssh/sshd_config
    sed -i 's|#Compression.*|Compression delayed|g' /etc/ssh/sshd_config
    sed -i 's|Compression.*|Compression delayed|g' /etc/ssh/sshd_config
    if ! grep -q 'HostbasedAuthentication' /etc/ssh/sshd_config; then
        echo 'HostbasedAuthentication no' >> /etc/ssh/sshd_config
    fi
    sed -i 's|#HostbasedAuthentication.*|HostbasedAuthentication no|g' /etc/ssh/sshd_config
    sed -i 's|HostbasedAuthentication.*|HostbasedAuthentication no|g' /etc/ssh/sshd_config
    sed -i 's|#PrintLastLog.*|PrintLastLog yes|g' /etc/ssh/sshd_config
    sed -i 's|PrintLastLog.*|PrintLastLog yes|g' /etc/ssh/sshd_config
    sed -i 's|#IgnoreRhosts.*|IgnoreRhosts yes|g' /etc/ssh/sshd_config
    sed -i 's|IgnoreRhosts.*|IgnoreRhosts yes|g' /etc/ssh/sshd_config
    sed -i "s/Port .*/Port $SSH_PORT/g" /etc/ssh/sshd_config
    sed -i "s/#Port ${SSH_PORT}/Port ${SSH_PORT}/g" /etc/ssh/sshd_config
    sed -i 's|#PermitEmptyPasswords.*|PermitEmptyPasswords no|g' /etc/ssh/sshd_config
    sed -i 's|PermitEmptyPasswords.*|PermitEmptyPasswords no|g' /etc/ssh/sshd_config
    sed -i 's/PermitRootLogin.*/PermitRootLogin no/g' /etc/ssh/sshd_config
    sed -i 's/#PermitRootLogin no/PermitRootLogin no/g' /etc/ssh/sshd_config
    sed -i 's/X11Forwarding.*/X11Forwarding no/g' /etc/ssh/sshd_config
    sed -i 's/#X11Forwarding no/X11Forwarding no/g' /etc/ssh/sshd_config
    sed -i 's/ServerKeyBits.*/ServerKeyBits 2048/g' /etc/ssh/sshd_config
    sed -i 's/#ServerKeyBits 2048/ServerKeyBits 2048/g' /etc/ssh/sshd_config
    sed -i 's/TCPKeepAlive.*/TCPKeepAlive no/g' /etc/ssh/sshd_config
    sed -i 's/#TCPKeepAlive no/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
    sed -i 's|#HostKey /etc/ssh/ssh_host_ed25519_key|HostKey /etc/ssh/ssh_host_ed25519_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
    sed -i 's/#ClientAliveInterval 60/ClientAliveInterval 60/g' /etc/ssh/sshd_config
    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
    sed -i 's/#ClientAliveCountMax 3/ClientAliveCountMax 3/g' /etc/ssh/sshd_config
    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
    sed -i "s|#Ciphers $SSH_CIPHERS|Ciphers $SSH_CIPHERS|g" /etc/ssh/sshd_config
    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
    sed -i "s|#MACs $SSH_MACS|MACs $SSH_MACS|g" /etc/ssh/sshd_config
    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
    sed -i "s|#KexAlgorithms $SSH_KEX|KexAlgorithms $SSH_KEX|g" /etc/ssh/sshd_config
    if ! grep -q 'UsePrivilegeSeparation' /etc/ssh/sshd_config; then
        echo 'UsePrivilegeSeparation sandbox' >> /etc/ssh/sshd_config
    fi
    sed -i 's|#UsePrivilegeSeparation .*|UsePrivilegeSeparation sandbox|g' /etc/ssh/sshd_config
    sed -i 's|UsePrivilegeSeparation .*|UsePrivilegeSeparation sandbox|g' /etc/ssh/sshd_config

    apt-get -yq install vim-common

    function_check configure_firewall_for_ssh
    configure_firewall_for_ssh
    mark_completed "${FUNCNAME[0]}"
}

# 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[0]}") == "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 2048 -o -a 100
    #fi

    function_check ssh_remove_small_moduli
    ssh_remove_small_moduli
    mark_completed "${FUNCNAME[0]}"
}

function regenerate_ssh_keys {
    if [[ $(is_completed "${FUNCNAME[0]}") == "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[0]}"
}

function configure_firewall_for_ssh {
    if [[ $(is_completed "${FUNCNAME[0]}") == "1" ]]; then
        return
    fi
    if [[ $INSTALLED_WITHIN_DOCKER == "yes" ]]; then
        # docker does its own firewalling
        return
    fi

    firewall_add SSH ${SSH_PORT} tcp
    mark_completed "${FUNCNAME[0]}"
}

function get_ssh_server_key {
    if [ -f /etc/ssh/ssh_host_rsa_key.pub ]; then
        echo "RSA Md5:       $(ssh-keygen -lf /etc/ssh/ssh_host_rsa_key.pub | awk -F ' ' '{print $2}')"
        echo "RSA SHA256:    $(awk '{print $2}' /etc/ssh/ssh_host_rsa_key.pub | base64 -d | sha256sum -b | awk '{print $1}' | xxd -r -p | base64 | sed 's|=||g')"
    fi
    if [ -f /etc/ssh/ssh_host_ed25519_key.pub ]; then
        echo "ED25519 Md5:   $(ssh-keygen -lf /etc/ssh/ssh_host_ed25519_key.pub | awk -F ' ' '{print $2}')"
        echo "ED25519 SHA256:$(awk '{print $2}' /etc/ssh/ssh_host_ed25519_key.pub | base64 -d | sha256sum -b | awk '{print $1}' | xxd -r -p | base64 | sed 's|=||g')"
    fi
}

# NOTE: deliberately no exit 0