Hak5 2019 – Linux Server Build: OpenVPN From Scratch

Today we’re building an OpenVPN server from scratch in Linux!
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Install and setup OpenVPN

apt-get update; apt-get install openvpn easy-rsa

gunzip -c /usr/share/doc/openvpn/examples/sample-config-files/server.conf.gz /etc/openvpn/server.conf

nano /etc/openvpn/server.conf

replace dh1024.pem with dh2048.pem
#uncomment push “redirect-gateway def1 bypass-dhcp”
#uncomment push “dhcp-option DNS” and replace IP addresses with your fav DNS
#uncomment user nobody
#uncomment group nogroup
#save and exit

Setup Firewall

#Enable IP forwarding
echo 1 /proc/sys/net/ipv4/ip_forward

nano /etc/sysctl.conf
#uncomment net.ipv4.ip_forward=1
#save and exit

#Configure firewall.

ufw status
ufw allow ssh
ufw allow 1194/udp

#Let packets forward through the VPS by changing for forward policy to accept

nano /etc/default/ufw
#replace DROP with ACCEPT in DEFAULT_FORWARD_POLICY=”DROP”
#save and exit

#Enable NAT and IP masquerading for clients
nano /etc/ufw/before.rules
#Add the following near the top
*nat
:POSTROUTING ACCEPT [0:0]
-A POSTROUTING -s 10.8.0.0/8 -o eth0 -j MASQUERADE
COMMIT

ufw status

Setup Keys and Start the Server

cp -r /usr/share/easy-rsa/ /etc/openvpn
mkdir /etc/openvpn/easy-rsa/keys

nano /etc/openvpn/easy-rsa/vars
#change export KEY_* values
#set KEY_NAME to “server”
#save and exit

#Generate the 2048 bit Diffie-Hellman pem file we pointed to in the openvpn config
openssl dhparam -out /etc/openvpn/dh2048.pem 2048

#move to the easy-rsa directory

cd /etc/openvpn/easy-rsa

#Set the variables we configured
. ./vars
./clean-all
./build-ca #Accept all defaults
./build-key-server server #Accept all defaults

#Move the newly generated certificates to /etc/openvpn
cp /etc/openvpn/easy-rsa/keys/server.crt,server.key,ca.crt /etc/openvpn

#In /etc/openvpn we should have a server.conf, server.crt, server.key, ca.crt and dh2048.pem

#start the OpenVPN service
service openvpn start
service openvpn status

Setup keys for the first client

./build-key client
ls keys

#Make a new directory to merge the client configuration and keys
mkdir ~/client

#Copy the example client configuration renaming the file extension from conf to ovpn
cp /usr/share/doc/openvpn/examples/sample-config-files/client.conf ~/client/pineapple.ovpn

cd /etc/openvpn/easy-rsa/keys
cp client.crt client.key client.ovpn ~/client
cp /etc/openvpn/ca.crt ~/client

Securely copy client.crt, client.key, ca.crt and client.ovpn to your client device

cd ~/client

#determine public IP address
ifconfig

nano pineapple.ovpn
# find remote and replace my-server-1 with IP address of VPN server
# uncomment group nogroup
# uncomment user nobody
# comment out the ca, cert and key directives
# save and exit

echo “ca” to pineapple.ovpn
cat ca.crt to pineapple.ovpn
echo “/ca” to pineapple.ovpn

echo “cert” to pineapple.ovpn
cat client.crt to pineapple.ovpn
echo “/cert” to pineapple.ovpn

echo “key” to pineapple.ovpn
cat client.key to pineapple.ovpn
echo “/key” to pineapple.ovpn

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