OpenVPN (Ubuntu 18.04)

Installation

Um die Installation anzuzeigen bitte aufklappen

sudo apt-get install openvpn easy-rsa 

Ordner zur Schlüsselerzeugung kopieren:

sudo cp -r /usr/share/easy-rsa /etc/openvpn/easy-rsa2 

Konfiguration

Um die allgemeine Konfiguration anzuzeigen bitte aufklappen

Schlüssel und Zertifikate generieren

Variablen anpassen

In das RSA-Verzeichnis wechseln:

cd /etc/openvpn/easy-rsa2/

Die Datei /etc/openvpn/easy-rsa2/vars kopieren

sudo cp vars.example vars
sudo nano vars

und folgende Zeilen einkommenieren und anpassen (nicht leer lassen):

#set_var EASYRSA_REQ_COUNTRY    "US"
#set_var EASYRSA_REQ_PROVINCE   "California"
#set_var EASYRSA_REQ_CITY       "San Francisco"
#set_var EASYRSA_REQ_ORG        "Copyleft Certificate Co"
#set_var EASYRSA_REQ_EMAIL      "me@example.net"
#set_var EASYRSA_REQ_OU         "My Organizational Unit"

...

#set_var EASYRSA_KEY_SIZE        2048

Certificate Authority (CA) erstellen

sudo ./easyrsa init-pki
sudo ./easyrsa build-ca nopass

Bei der Frage Common Name (eg: your user, host, or server name) [Easy-RSA CA]: einfach ENTER klicken.

Server Schlüssel erstellen

Mittels folgendem Befehl wird ein Server-Schlüssel und ein Zertifikatsantrag erstellt:

sudo ./easyrsa gen-req server nopass

Bei der Frage nach dem Common Name einfach den Standardwert server übernehmen.

Danach muss der Zertifikatsantrag von der CA unterschrieben werde:

sudo ./easyrsa sign-req server server

Diffie-Hellman-Schlüssel für den Austausch

sudo ./easyrsa gen-dh

Keyed-Hash Message Authentication Code

cd /etc/openvpn/server
sudo openvpn --genkey --secret ta.key

Client-Zertifikat und Schlüssel

Schlüssel und Zertifikatsantrag erstellen:

sudo ./easyrsa gen-req client1 nopass

Bei der Frage nach dem Common Name einfach den Standardwert server übernehmen.

Der Zertifikatsantrag muss, wie beim Server, wieder von der CA unterschrieben werden:

sudo ./easyrsa sign-req client client1

Danach die Dateien in ein Verzeichnis pro Client kopieren und ein TAR-Archiv daraus erstellen:

sudo su
mkdir -p /etc/openvpn/easy-rsa2/client-configs/client1/keys 
chmod -R 700 /etc/openvpn/easy-rsa2/client-configs 

cp /etc/openvpn/easy-rsa2/pki/issued/client1.crt /etc/openvpn/easy-rsa2/client-configs/client1/keys
cp /etc/openvpn/easy-rsa2/pki/private/client1.key /etc/openvpn/easy-rsa2/client-configs/client1/keys
cp /etc/openvpn/easy-rsa2/pki/ca.crt /etc/openvpn/easy-rsa2/client-configs/client1/keys
cp /etc/openvpn/server/ta.key /etc/openvpn/easy-rsa2/client-configs/client1/keys

cd client-configs/client1/
tar -czf client1.tgz keys/*
exit

Auflistung aller Serverdateien

Die für die Serverkonfiguration benötigten Dateien liegen danach unter folgenden Verzeichnissen:

../easy-rsa2/pki/ca.crt
../easy-rsa2/pki/issued/server.crt
../easy-rsa2/pki/private/server.key
../easy-rsa2/pki/dh.pem

Server Konfiguration

Um die Server-Konfiguration anzuzeigen bitte aufklappen

IPV4-Weiterleitung aktivieren

Siehe dazu Netzwerk einrichten (Linux)

Benutzer openvpn anlegen

Zur Erhöhung der Sicherheit wird der Server mit dem Benutzer openvpn ausgeführt.

Zum Anlegen eines systemspezifischen Benutzers siehe User Administration

Beispeil einer server.conf-Konfigurationsdatei

#################################################
# Sample OpenVPN 2.0 config file for            #
# multi-client server.                          #
#                                               #
# This file is for the server side              #
# of a many-clients <-> one-server              #
# OpenVPN configuration.                        #
#                                               #
# OpenVPN also supports                         #
# single-machine <-> single-machine             #
# configurations (See the Examples page         #
# on the web site for more info).               #
#                                               #
# This config should work on Windows            #
# or Linux/BSD systems.  Remember on            #
# Windows to quote pathnames and use            #
# double backslashes, e.g.:                     #
# "C:\\Program Files\\OpenVPN\\config\\foo.key" #
#                                               #
# Comments are preceded with '#' or ';'         #
#################################################

# Which local IP address should OpenVPN
# listen on? (optional)
local 10.0.0.101

# Which TCP/UDP port should OpenVPN listen on?
# If you want to run multiple OpenVPN instances
# on the same machine, use a different port
# number for each one.  You will need to
# open up this port on your firewall.
port 10000

# TCP or UDP server?
;proto tcp
proto udp

# "dev tun" will create a routed IP tunnel,
# "dev tap" will create an ethernet tunnel.
# Use "dev tap0" if you are ethernet bridging
# and have precreated a tap0 virtual interface
# and bridged it with your ethernet interface.
# If you want to control access policies
# over the VPN, you must create firewall
# rules for the the TUN/TAP interface.
# On non-Windows systems, you can give
# an explicit unit number, such as tun0.
# On Windows, use "dev-node" for this.
# On most systems, the VPN will not function
# unless you partially or fully disable
# the firewall for the TUN/TAP interface.
;dev tap
dev tun

# SSL/TLS root certificate (ca), certificate
# (cert), and private key (key).  Each client
# and the server must have their own cert and
# key file.  The server and all clients will
# use the same ca file.
#
# See the "easy-rsa" directory for a series
# of scripts for generating RSA certificates
# and private keys.  Remember to use
# a unique Common Name for the server
# and each of the client certificates.
#
# Any X509 key management system can be used.
# OpenVPN can also use a PKCS #12 formatted key file
# (see "pkcs12" directive in man page).
ca ./easy-rsa2/keys/ca.crt
cert ./easy-rsa2/keys/server.crt
key ./easy-rsa2/keys/server.key  # This file should be kept secret

# Diffie hellman parameters.
# Generate your own with:
#   openssl dhparam -out dh1024.pem 1024
# Substitute 2048 for 1024 if you are using
# 2048 bit keys. 
dh ./easy-rsa2/keys/dh2048.pem

# Configure server mode and supply a VPN subnet
# for OpenVPN to draw client addresses from.
# The server will take 10.8.0.1 for itself,
# the rest will be made available to clients.
# Each client will be able to reach the server
# on 10.8.0.1. Comment this line out if you are
# ethernet bridging. See the man page for more info.
server 10.8.0.0 255.255.255.0

# In subnet topology, the tun device is configured
# with an IP and netmask like a "traditional" 
# broadcast-based network.
topology subnet

# Maintain a record of client <-> virtual IP address
# associations in this file.  If OpenVPN goes down or
# is restarted, reconnecting clients can be assigned
# the same virtual IP address from the pool that was
# previously assigned.
ifconfig-pool-persist ipp.txt

# Push routes to the client to allow it
# to reach other private subnets behind
# the server.  Remember that these
# private subnets will also need
# to know to route the OpenVPN client
# address pool (10.8.0.0/255.255.255.0)
# back to the OpenVPN server.
push "route 10.0.0.0 255.255.255.0"

# If enabled, this directive will configure
# all clients to redirect their default
# network gateway through the VPN, causing
# all IP traffic such as web browsing and
# and DNS lookups to go through the VPN
# (The OpenVPN server machine may need to NAT
# or bridge the TUN/TAP interface to the internet
# in order for this to work properly).
push "redirect-gateway def1 bypass-dhcp"

# Certain Windows-specific network settings
# can be pushed to clients, such as DNS
# or WINS server addresses.  CAVEAT:
# http://openvpn.net/faq.html#dhcpcaveats
# The addresses below refer to the public
# DNS servers provided by opendns.com.
push "dhcp-option DNS 10.0.0.101"
;push "dhcp-option DNS 208.67.220.220"

# The keepalive directive causes ping-like
# messages to be sent back and forth over
# the link so that each side knows when
# the other side has gone down.
# Ping every 10 seconds, assume that remote
# peer is down if no ping received during
# a 120 second time period.
keepalive 10 120

# Select a cryptographic cipher.
# This config item must be copied to
# the client config file as well.
;cipher BF-CBC        # Blowfish (default)
cipher AES-256-CBC   # AES
;cipher DES-EDE3-CBC  # Triple-DES

# Enable compression on the VPN link.
# If you enable it here, you must also
# enable it in the client config file.
comp-lzo

# It's a good idea to reduce the OpenVPN
# daemon's privileges after initialization.
#
# You can uncomment this out on
# non-Windows systems.
user openvpn
group openvpn

# The persist options will try to avoid
# accessing certain resources on restart
# that may no longer be accessible because
# of the privilege downgrade.
persist-key
persist-tun

# Output a short status file showing
# current connections, truncated
# and rewritten every minute.
status openvpn-status.log

# By default, log messages will go to the syslog (or
# on Windows, if running as a service, they will go to
# the "\Program Files\OpenVPN\log" directory).
# Use log or log-append to override this default.
# "log" will truncate the log file on OpenVPN startup,
# while "log-append" will append to it.  Use one
# or the other (but not both).
;log         openvpn.log
log-append  openvpn.log

# Set the appropriate level of log
# file verbosity.
#
# 0 is silent, except for fatal errors
# 4 is reasonable for general usage
# 5 and 6 can help to debug connection problems
# 9 is extremely verbose
verb 3

tls-server
auth SHA1

script-security 3 execve
auth-user-pass-verify checklogin.sh via-env

# This directive sets a client configuration directory,
# which the OpenVPN server will scan for every 
# incomming connection, searching for a client specific
# configuration file.
client-config-dir ccd

Script checklogin.sh

cd /etc/openvpn/
sudo nano checklogin.sh

#!/bin/bash
# zur Sicherheit

if [ "$username" == "" -o "$password" == "" ] ; then
  exit 1
fi

# Username und Passwort werden zusammengesetzt
USER_PASS="$username:$password"

# der Eintrag wird in der Datei users gesucht
cat ./users | grep $USER_PASS > /dev/null

# wenn grep den Eintrag gefunden hat, ist der Exitcode 0
exit $?

Besitzer ändern und ausführbar machen:

sudo chown openvpn:openvpn checklogin.sh
sudo chmod a+x checklogin.sh

Inhalt der Datei users

sudo nano users

Benutzer:Passwort
<user name>:<password>

sudo chown openvpn:openvpn users

client config dir (ccd)

Mit einer Datei im client config dir-Verzeichnis kann man einem Client eine statische IP-Adresse zuordnen

Zuerst ein Verzeichnis anlegen (muss mit der Direktive client-config-dir übereinstimmen), wo alle Dateien abgelegt werden:

cd /etc/openvpn/
sudo mkdir ccd

Danach eine Datei mit der Angabe Common Name beim Benutzerschlüssel anlegen:

sudo nano ccd/<common name>

Und folgenden Inhalt eintragen:

ifconfig-push <ip address> <net mask>

z.B.

ifconfig-push 10.8.0.8 255.255.255.0

Links

https://www.digitalocean.com/community/tutorials/how-to-set-up-an-openvpn-server-on-debian-10

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