Ubuntu/OpenVPN Server

Server Prep

Install OpenVPN

Update and install, this should have been completed earlier for the PIA VPN tunnel:

sudo apt update
sudo apt -y install openvpn

Install EasyRSA

Obtain and install EasyRSA to create a certificate authority and certificates for the server:

wget -qO- https://github.com/OpenVPN/easy-rsa/releases/download/2.2.2/EasyRSA-2.2.2.tgz | tar xvz -C /opt/
cp -R /opt/EasyRSA-2.2.2 /opt/easy-rsa
ln -fs /opt/easy-rsa/openssl-1.0.0.cnf /opt/easy-rsa/openssl.cnf

Setup OpenVPN Server

Set local EasyRSA variables for the certificate.

/opt/easy-rsa/local_vars

export KEY_COUNTRY="US"
export KEY_PROVINCE="CA"
export KEY_CITY="Santa Cruz"
export KEY_ORG="charlesreid1.com"
export KEY_OU="bespin VPN"
export KEY_EMAIL=""
export KEY_NAME="bespin VPN key"

Set permissions and ownership:

chmod 0644 /opt/easy-rsa/local_vars
chown root:root /opt/easy-rsa/local_vars

Prepare to generate secrets:

cd /opt/easy-rsa

Clean keys directory:

test -e /opt/easy-rsa/clean-all
. /opt/easy-rsa/vars;. /opt/easy-rsa/local_vars;/opt/easy-rsa/clean-all

Build certificate - make script non-interactive, then run:

test -e /opt/easy-rsa/build-ca
sed -i 's/--interact//g' /opt/easy-rsa/build-ca
. /opt/easy-rsa/vars;. /opt/easy-rsa/local_vars;/opt/easy-rsa/build-ca

Build DH parameters:

test -e /opt/easy-rsa/build-dh
. /opt/easy-rsa/vars;. /opt/easy-rsa/local_vars;/opt/easy-rsa/build-dh

Build key - make script non-interactive, then run:

test -e /opt/easy-rsa/build-key-server
sed -i 's/--interact//g' /opt/easy-rsa/build-key-server
. /opt/easy-rsa/vars;. /opt/easy-rsa/local_vars;/opt/easy-rsa/build-key-server server

Make keys directory:

mkdir -p /opt/easy-rsa/keys
cd /opt/easy-rsa/keys

Generate static TLS secret:

openvpn --genkey --secret statictlssecret.key

Configure VPN Server

Here we configure the VPN so that VPN IP addresses are in the CIDR block 10.10.10.0/24.

/etc/openvpn/server.conf

port 1194
proto udp
dev tun
server 10.101.0.0 255.255.255.0
# enable this line to tunnel all client traffic thru vpn
#push "redirect-gateway def1"
# use dnsmasq as a dns server
push "dhcp-option DNS 10.10.10.1"

ca /opt/easy-rsa/keys/ca.crt
cert /opt/easy-rsa/keys/server.crt
key /opt/easy-rsa/keys/server.key
dh /opt/easy-rsa/keys/dh2048.pem

tls-auth statictlssecret.key 0

# use pam for auth
plugin /usr/lib/x86_64-linux-gnu/openvpn/plugins/openvpn-plugin-auth-pam.so openvpn
# custom client configurations
client-config-dir /etc/openvpn/clients

Configure VPN Server Startup Service

Run this command to update the openvpn@ startup service to send separate logs for separate openvpn networks into their own log files:

sed -i 's|^ExecStart=.*|& --log-append /var/log/openvpn.%i.log|' /lib/systemd/system/openvpn@.service

A Note on the OpenVPN Startup Service

Quick side note to explain /lib/systemd/system/openvpn@.service:

This is a TEMPLATED startup service that allows you to run multiple startup services for multiple instances of openvpn for multiple VPNs. If you run service openvpn@myvpn start, it will start OpenVPN with the configuration file myvpn.conf.

Enable and Start VPN Server Service

Given that our OpenVPN server config file is in server.conf in /etc/openvpn, we can start an OpenVPN service with this config file like this:

systemctl enable openvpn@server.service
systemctl start openvpn@server.service

Configure iptables

The way we plan on doing this, we're just going to use the VPN tunnel to be able to reach bespin. There is no need to share networks.

But what DNS server will the new VPN use? Do we need a new DHCP server too? Can we handle DNS for tun1 too? Do we need to set up another dnsmasq instance?

No network management needed, OpenVPN handles assigning IPs, so if it is a standalone plain network, nope, no new servers needed.

Configure PAM

PAM is the pluggable authentication module in Linux. It provides a variety of methods for authenticating users in various contexts (for example, when you log into a desktop computer).

In the OpenVPN server config file, we included the following line to use PAM for authentication:

# use pam for auth
plugin /usr/lib/x86_64-linux-gnu/openvpn/plugins/openvpn-plugin-auth-pam.so openvpn

This corresponds to a configuration file /etc/pam.d/openvpn that contains directives telling PAM how OpenVPN wants to authenticate users.

We can use Unix usernames/passwords to authenticate users:

/etc/pam.d/openvpn

auth required pam_unix.so

Adding MFA to VPN Access

To add MFA to the VPN access (note: this will require changes to how users are created below), first install the Google Authenticator PAM library and other utilities:

apt-get -y install libpam-google-authenticator libqrencode3 qrencode

Now modify the contents of /etc/pam.d/openvpn to replace the Unix login with Google Authenticator as a method of authentication:

/etc/pam.d/openvpn

auth required /lib/x86_64-linux-gnu/security/pam_google_authenticator.so secret=/etc/openvpn/google-authenticator/${USER} user=gauth try_first_pass

Also need to create a gauth user to handle Google Authenticator stuff:

addgroup gauth && useradd -g gauth gauth

Create the Google Authenticator directory:

mkdir /etc/openvpn/google-authenticator

Set ownership and permissions:

chown gauth:gauth /etc/openvpn/google-authenticator
chmod 0700 /etc/openvpn/google-authenticator

Starting the OpenVPN Server

If your OpenVPN server config file is at /etc/openvpn/server.conf then you can enable and start the service with these commands:

sudo systemctl enable openvpn@server
sudo systemctl start openvpn@server

Verify the service starts okay by monitoring the syslog in another window:

sudo tail -f /var/log/syslog

Verify the tun0 interface came up

Client Prep

Setup OpenVPN Client

Fix up the build key script so that it is non-interactive and has correct paths:

sed -i 's/--interact//g' /opt/easy-rsa/build-key
sed -i 's+export EASY_RSA=.*+export EASY_RSA="/opt/easy-rsa"+' /opt/easy-rsa/build-key

Add a custom client config directory:

mkdir -p /etc/openvpn/clients

Configure OpenVPN Client

Configure the OopenVPN client by creating a client config file:

/opt/easy-rsa/openvpn_client.conf

client
dev tun
proto udp
remote REMOTEIPOFOPENVPNSERVERGOESHERE 1194
nobind
pull
persist-key
persist-tun
remote-cert-tls server
ca ca.crt
cert clientuser.crt
key clientuser.key
tls-auth statictlssecret.key 1
auth-user-pass

Create Utility Scripts

We are going to create a couple of scripts to accomplish the task of registering users for the OpenVPN network.

First let's install some utilities that we will use.

Install Utility Helpers

sudo apt-get -y install zip unzip

Generate OpenVPN Profile

/opt/easy-rsa/gen_ovpn_profile.sh

#!/bin/bash
# Called by gen_client.sh
# Usage: ./gen_ovpn_profile.sh [USERNAME]
set -e
test "$#" -eq "1" || { echo "Provide 1 argument (username)"; exit 1; }
test -e /opt/openvpn/openvpn_client.conf || { echo "client config openvpn_client.conf not found!"; exit 1; }
test -e /opt/easy-rsa/keys/${1}.key || { echo "client key ${1} not found!"; exit 1; }
test -e /opt/easy-rsa/keys/ca.crt || { echo "server certificate ca.crt not found!"; exit 1; }
(cat /opt/openvpn/openvpn_client.conf
echo '<key>'
cat /opt/easy-rsa/keys/${1}.key
echo '</key>'
echo '<cert>'
cat /opt/easy-rsa/keys/${1}.crt
echo '</cert>'
echo '<ca>'
cat /opt/easy-rsa/keys/ca.crt
echo '</ca>'
) > /opt/easy-rsa/keys/openvpn_${1}.ovpn

Set ownership and permissions:

chmod 0700 /opt/easy-rsa/gen_ovpn_profile.sh
chown root:root /opt/easy-rsa/gen_ovpn_profile.sh

Zip Client Files

/opt/easy-rsa/zip_client_files.sh

#!/bin/bash
# Called by gen_client.sh
# Usage: ./zip_client_files.sh [USERNAME]
set -e
test "$#" -eq "1" || { echo "Provide 1 argument (username)"; exit 1; }
FILES="/opt/easy-rsa/keys/ca.crt
/opt/easy-rsa/keys/statictlssecret.key
/opt/easy-rsa/keys/${1}.key
/opt/easy-rsa/keys/${1}.crt
/opt/easy-rsa/keys/openvpn_${1}.ovpn
/opt/easy-rsa/README
/opt/easy-rsa/keys/${1}_password.txt"
cat /opt/easy-rsa/README_LOGIN > /opt/easy-rsa/README
for fname in ${FILES}; do
    test -e ${fname} || { echo "File ${fname} not found!"; exit 1; }
done
cd /opt/easy-rsa/keys
zip -j ${1}.zip $FILES
rm -f /opt/easy-rsa/README

Set ownership and permissions:

chmod 0700 /opt/easy-rsa/zip_client_files.sh
chown root:root /opt/easy-rsa/zip_client_files.sh

Zip Client Files MFA Version

If you are setting up MFA, change the scripts as follows:

/opt/easy-rsa/zip_client_files.sh

#!/bin/bash
# Called by gen_client.sh
# Usage: ./zip_client_files.sh [USERNAME]
# Set the MFA_DISABLED env var to any value to use script for non-MFA clients
set -e
test "$#" -eq "1" || { echo "Provide 1 argument (username)"; exit 1; }
FILES="/opt/easy-rsa/keys/ca.crt
/opt/easy-rsa/keys/statictlssecret.key
/opt/easy-rsa/keys/${1}.key
/opt/easy-rsa/keys/${1}.crt
/opt/easy-rsa/keys/openvpn_${1}.ovpn
/opt/easy-rsa/README"
if [ -z "${MFA_DISABLED}" ]; then
    FILES="${FILES}
    /etc/openvpn/google-authenticator/${1}_qr.png
    /etc/openvpn/google-authenticator/${1}_backup_codes.txt"
    cat /opt/easy-rsa/README_MFA > /opt/easy-rsa/README
else
    FILES="${FILES}
    /opt/easy-rsa/keys/${1}_password.txt"
    cat /opt/easy-rsa/README_LOGIN > /opt/easy-rsa/README
fi
for fname in ${FILES}; do
    test -e ${fname} || { echo "File ${fname} not found!"; exit 1; }
done
cd /opt/easy-rsa/keys
zip -j ${1}.zip $FILES
rm -f /opt/easy-rsa/README

Generate and Delete Client Scripts

Generate Client Script

/opt/easy-rsa/gen_client.sh

#!/bin/bash
# Create new client and files required by new client.
# Usage: ./gen_client.sh [USERNAME]
set -e
test "$#" -eq "1" || { echo "Provide 1 argument (username)"; exit 1; }
# Run build-key
test -e /opt/easy-rsa/build-key || { echo "build-key not found!"; exit 1; }
test -e /opt/easy-rsa/gen_ovpn_profile.sh || { echo "gen_ovpn_profile.sh not found!"; exit 1; }
. /opt/easy-rsa/vars
. /opt/easy-rsa/local_vars
/opt/easy-rsa/build-key ${1}
# Generate .ovpn profile
test -e /opt/easy-rsa/keys/${1}.crt || { echo "client certificate ${1} not found!"; exit 1; }
/opt/easy-rsa/gen_ovpn_profile.sh ${1}
# Register unix user and set a password
useradd -s /bin/nologin "${1}"
# Login user needs password
head /dev/urandom | tr -dc A-Za-z0-9 | head -c 13 > /opt/easy-rsa/keys/${1}_password.txt
echo "${1}:$(cat /opt/easy-rsa/keys/${1}_password.txt)" | chpasswd
# Zip up all the client's files
/opt/easy-rsa/zip_client_files.sh ${1}
rm -f /opt/easy-rsa/keys/${1}_password.txt

Set ownership and permissions:

chmod 0700 /opt/easy-rsa/gen_client.sh
chown root:root /opt/easy-rsa/gen_client.sh

Generate Client Script MFA Version

If you are using MFA to protect the VPN, change the generate client script to the following:

/opt/easy-rsa/gen_client.sh

#!/bin/bash
# Create new client and files required by new client.
# Usage: ./gen_client.sh [USERNAME]
# Set the MFA_DISABLED env var to any value to use script for non-MFA clients
set -e
test "$#" -eq "1" || { echo "Provide 1 argument (username)"; exit 1; }
# Run build-key
test -e /opt/easy-rsa/build-key || { echo "build-key not found!"; exit 1; }
test -e /opt/easy-rsa/gen_ovpn_profile.sh || { echo "gen_ovpn_profile.sh not found!"; exit 1; }
. /opt/easy-rsa/vars
. /opt/easy-rsa/local_vars
/opt/easy-rsa/build-key ${1}
# Generate .ovpn profile
test -e /opt/easy-rsa/keys/${1}.crt || { echo "client certificate ${1} not found!"; exit 1; }
/opt/easy-rsa/gen_ovpn_profile.sh ${1}
# Register unix user and set a password
useradd -s /bin/nologin "${1}"
if [ -n "${MFA_DISABLED}" ]; then
    # Login user needs password
    head /dev/urandom | tr -dc A-Za-z0-9 | head -c 13 > /opt/easy-rsa/keys/${1}_password.txt
    echo "${1}:$(cat /opt/easy-rsa/keys/${1}_password.txt)" | chpasswd
else
    # MFA user does not need password
    echo "${1}:$(head /dev/urandom | tr -dc A-Za-z0-9 | head -c 13)" | chpasswd
    # Generate MFA client info
    MFA_LABEL="Dockstore VPN"
    sudo -H -u gauth google-authenticator -t -w3 -e10 -d -r3 -R30 -f -l "${MFA_LABEL}" -s /etc/openvpn/google-authenticator/${1} > /etc/openvpn/google-authenticator/${1}.log
    # Text file with MFA backup codes
    tail -n10 /etc/openvpn/google-authenticator/${1} > /etc/openvpn/google-authenticator/${1}_backup_codes.txt
    # Generate QR image
    AUTH_ID="$( head -n1 /etc/openvpn/google-authenticator/${1} )"
    qrencode -o /etc/openvpn/google-authenticator/${1}_qr.png -d 300 -s 10 "otpauth://totp/${1}?secret=${AUTH_ID}&issuer=${MFA_LABEL}"
fi
# Zip up all the client's files
/opt/easy-rsa/zip_client_files.sh ${1}
if [ -n "${MFA_DISABLED}" ]; then
    rm -f /opt/easy-rsa/keys/${1}_password.txt
fi

Delete Client Script

/opt/easy-rsa/del_client.sh

#!/bin/bash
# Delete a client by deleting their client files and unix user.
# Usage: ./del_client.sh [USERNAME]
set -e
test "$#" -eq "1" || { echo "Provide 1 argument (username"; exit 1; }
# Revoke client files
. /opt/easy-rsa/vars
. /opt/easy-rsa/local_vars
/opt/easy-rsa/revoke-full ${1}
# Delete client openvpn files
rm -f /opt/easy-rsa/keys/${1}.zip
rm -f /opt/easy-rsa/keys/${1}.key
rm -f /opt/easy-rsa/keys/openvpn_${1}.ovpn
# Delete unix user
deluser --remove-home ${1}
echo "User account ${1} has been deleted"

Set ownership and permissions:

chmod 0700 /opt/easy-rsa/del_client.sh
chown root:root /opt/easy-rsa/del_client.sh

Delete Client Script MFA Version

/opt/easy-rsa/del_client.sh

#!/bin/bash
# Delete a client by deleting their client files and unix user.
# Usage: ./del_client.sh [USERNAME]
set -e
test "$#" -eq "1" || { echo "Provide 1 argument (username"; exit 1; }
# Revoke client files
. /opt/easy-rsa/vars
. /opt/easy-rsa/local_vars
/opt/easy-rsa/revoke-full ${1}
# Delete client openvpn files
rm -f /opt/easy-rsa/keys/${1}.zip
rm -f /opt/easy-rsa/keys/${1}.key
rm -f /opt/easy-rsa/keys/openvpn_${1}.ovpn
# Delete client MFA files (if they exist)
rm -f /etc/openvpn/google-authenticator/${1}
rm -f /etc/openvpn/google-authenticator/${1}.log
rm -f /etc/openvpn/google-authenticator/${1}_qr.png
rm -f /etc/openvpn/google-authenticator/${1}_backup_codes.txt
# Delete unix user
deluser --remove-home ${1}
echo "User account ${1} has been deleted"

Using the VPN

Process for clients to use the VPN:

• Sign up a client using the gen_client.sh script. You specify the username with the first argument, and that's it.
• The gen client script will produce a zip file with the username of the client. This zip file should be securely transferred to the client.
• Clients unzip the file and use the contents to connect to the OpenVPN server. Use the .ovpn profile to connect, and use the username_password.txt file to log in.

Example: Create a New User

To create a new user:

cd /opt/easy-rsa/
./gen_client.sh <username>

Example: Create MFA and Non-MFA Users

If you have used the MFA versions of the scripts above, you can create an MFA user like so:

MFA_DISABLED="" ./gen_client.sh <username>

Similarly you can create a non-MFA user like so:

MFA_DISABLED="yes" ./gen_client.sh <username>