Difference between revisions of "VPN"

(Created page with "VIRTUAL PRIVATE NETWORK (VPN) =Introduction= ==Reminder: What is a “VPN”?== * French: http://www.frameip.com/vpn/ * English: ==Sources== * Linode: https://li...")
 
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[[Category:Linux]]
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VIRTUAL PRIVATE NETWORK (VPN)
 
VIRTUAL PRIVATE NETWORK (VPN)
  
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==Reminder: What is a “VPN”?==
 
==Reminder: What is a “VPN”?==
 +
 +
Nice explanations:
  
 
* French: http://www.frameip.com/vpn/  
 
* French: http://www.frameip.com/vpn/  
Line 12: Line 16:
  
  
==Sources==
 
  
* Linode: https://library.linode.com/networking/openvpn/debian-6-squeeze#sph_id7
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As a quick reminder, you can use a VPN for 3 things:
* WebSite (1) : http://dev.shyd.de/2011/02/dockstar-howto-setup-openvpn-debian/
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* Mask your source IP @
  
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[[File:VPN change ip address 1.png|none|VPN change ip address (1)]]
  
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[[File:VPN change ip address 2.png|none|VPN change ip address (2)]]
  
=Installation=
 
  
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* Secure communication through the VPN server
  
==Binary==
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[[File:VPN client to client.png|none|VPN client to client]]
  
Installation is easy. You just need “openvpn”.
 
  
<syntaxhighlight lang="bash">
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* Access remote LAN
apt-get update && upgrade
 
apt-get install openvpn
 
</syntaxhighlight>
 
  
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[[File:VPN to lan.png|none|VPN to LAN]]
  
==Logs==
 
  
Create target files
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Of course you can combine some / all of these usages.
  
<syntaxhighlight lang="bash">
 
touch /var/log/openvpn.log
 
touch /var/log/openvpn-status.log
 
chmod 777 /var/log/openvpn*
 
</syntaxhighlight>
 
  
Create symlinks
 
  
<syntaxhighlight lang="bash">
 
ln -s /var/log/openvpn.log /etc/openvpn/openvpn.log
 
ln -s /var/log/openvpn-status.log /etc/openvpn/openvpn-status.log
 
</syntaxhighlight>
 
  
Adjust '/etc/openvpn/server.conf' accordingly
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==Sources==
  
<syntaxhighlight lang="bash">
+
* Linode: https://library.linode.com/networking/openvpn/debian-6-squeeze#sph_id7
/var/log/openvpn.log => real time log
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* WebSite (1) : http://dev.shyd.de/2011/02/dockstar-howto-setup-openvpn-debian/
/var/log/openvpn-status.log => list of connected clients
 
</syntaxhighlight>
 
 
 
 
 
 
=Public Key Infrastructure=
 
 
 
The OpenVPN package provides a set of encryption-related tools called "easy-rsa".
 
These scripts are located by default in the ''/usr/share/doc/openvpn/examples/easy-rsa/'' directory.
 
However, in order to function properly, these scripts should be located in the /etc/openvpn directory.
 
 
 
 
 
==Installation==
 
 
 
Copy these files with the following command:
 
 
 
<syntaxhighlight lang="bash">
 
cp -R /usr/share/doc/openvpn/examples/easy-rsa/ /etc/openvpn
 
</syntaxhighlight>
 
 
 
 
 
==Configure Public Key Infrastructure Variables==
 
 
 
===Default values===
 
 
 
Before you can generate the public key infrastructure for OpenVPN, you must configure a few variables that the easy-rsa scripts will use to generate the scripts.
 
These variables are set near the end of the /etc/openvpn/easy-rsa/2.0/vars file.
 
 
 
 
 
<syntaxhighlight lang="bash">
 
vim /etc/openvpn/easy-rsa/2.0/vars
 
</syntaxhighlight>
 
 
 
Here is an example of the relevant values:
 
 
 
<syntaxhighlight lang="bash">
 
export KEY_COUNTRY="SE"
 
export KEY_PROVINCE="Västergötland"
 
export KEY_CITY="Goteborg"
 
export KEY_ORG="daxiongmao.eu"
 
export KEY_EMAIL="guillaume@qin-diaz.com"
 
</syntaxhighlight>
 
 
 
>> Alter the examples to reflect your configuration.
 
 
 
This information will be included in certificates you create!
 
That must be accurate, particularly the KEY_ORG and KEY_EMAIL values.
 
 
 
 
 
===Initialize the Public Key Infrastructure (PKI)===
 
 
 
Generate the Authority of Certification (AC):
 
 
 
 
 
<syntaxhighlight lang="bash">
 
cd /etc/openvpn/easy-rsa/2.0/
 
. /etc/openvpn/easy-rsa/2.0/vars
 
. /etc/openvpn/easy-rsa/2.0/clean-all
 
. /etc/openvpn/easy-rsa/2.0/build-ca
 
</syntaxhighlight>
 
 
 
 
 
===Generate OpenVPN Server Certificates and Private Key===
 
 
 
 
 
<syntaxhighlight lang="bash">
 
cd /etc/openvpn/easy-rsa/2.0/
 
source /etc/openvpn/easy-rsa/2.0/vars
 
. /etc/openvpn/easy-rsa/2.0/build-key-server server
 
</syntaxhighlight>
 
 
 
This script will also prompt you for additional information.
 
Common Name = Name of the current server (server DNS name)
 
 
 
 
 
===Generate Clients certificates and private keys===
 
 
 
 
 
<syntaxhighlight lang="bash">
 
cd /etc/openvpn/easy-rsa/2.0/
 
source /etc/openvpn/easy-rsa/2.0/vars
 
. /etc/openvpn/easy-rsa/2.0/build-key [clientName]
 
<syntaxhighlight lang="bash">
 
 
 
Replace the ''[clientName]'' parameter with a relevant identifier for each client.
 
* The client common name must be unique
 
* It helps you to identify each client. Don’t hesitate to use meaningful name.
 
 
 
The name is put inside the certificate.
 
 
 
All other information can remain the same
 
 
 
 
 
===Generate Diffie Hellman Parameters===
 
The "Diffie Hellman Parameters" govern the method of key exchange and authentication used by the OpenVPN server.
 
 
 
<syntaxhighlight lang="bash">
 
cd /etc/openvpn/easy-rsa/2.0/
 
. /etc/openvpn/easy-rsa/2.0/build-dh
 
</syntaxhighlight>
 
 
 
 
 
===Generate shared security key===
 
 
 
'''NOT TESTED – July 2013'''
 
 
 
To increase security, you can use a share common key between server and clients.
 
Each client will need the shared key + its own key to communicate.
 
 
 
 
 
<syntaxhighlight lang="bash">
 
openvpn --genkey --secret ./keys/ta.key
 
</syntaxhighlight>
 
 
 
 
 
==Distribute keys==
 
 
 
===Client files===
 
 
 
In order to authenticate to the VPN, you'll need to copy a number of certificate and key files to the remote client machines.
 
They are:
 
* Authority of certification ca.crt
 
* Client certificate [clientName].crt
 
* Client private key [clientName].key
 
 
 
!!! These keys should transferred with the utmost attention to security.
 
Anyone who has the key is able to gain full access to your virtual private network !!!
 
 
 
 
===Server files===
 
 
 
The keys and certificates for the server need to be relocated to the /etc/openvpn directory so the OpenVPN server process can access them.
 
These files are:
 
* Authority of certification ca.crt
 
* Authority private key ca.key
 
* Diffie Hellman props dh1024.pem
 
* Server certificate server.crt
 
* Server private key server.key
 
 
 
 
 
<syntaxhighlight lang="bash">
 
cd /etc/openvpn/
 
ln -s /etc/openvpn/easy-rsa/2.0/keys/ca.crt /etc/openvpn/ca.crt
 
ln -s /etc/openvpn/easy-rsa/2.0/keys/ca.key /etc/openvpn/ca.key
 
ln -s /etc/openvpn/easy-rsa/2.0/keys/dh1024.pem /etc/openvpn/dh1024.pem
 
ln -s /etc/openvpn/easy-rsa/2.0/keys/myServer.crt /etc/openvpn/server.crt
 
ln -s /etc/openvpn/easy-rsa/2.0/keys/myServer.key /etc/openvpn/server.key
 
</syntaxhighlight>
 
 
 
 
 
!! Apart 'ca.crt', all these files mustn't leave your server!!
 
 
 
 
 
==Revoking Client Certificates==
 
 
 
''How to remove a user's access to the VPN server?''
 
 
 
<syntaxhighlight lang="bash">
 
cd /etc/openvpn/easy-rsa/2.0/
 
. /etc/openvpn/easy-rsa/2.0/vars
 
. /etc/openvpn/easy-rsa/2.0/revoke-full [clientName]
 
</syntaxhighlight>
 
 
 
This will revoke the ability of users who have the [clientName] certificate to access the VPN.
 
 
 
For this reason, keeping track of which users are in possession of which certificates is crucial.
 
 
 
 
 
 
 
 
=Server configuration=
 
 
 
 
 
==Configuration file==
 
 
 
===Basic setup===
 
 
 
<syntaxhighlight lang="bash">
 
cp /usr/share/doc/openvpn/examples/sample-config-files/server.conf.gz /etc/openvpn
 
cd /etc/openvpn/
 
gzip -d server.conf.gz
 
</syntaxhighlight>
 
 
 
 
 
===Security algorithms and hash===
 
 
 
'''Cryptographic algorithms'''
 
<syntaxhighlight lang="bash">
 
openvpn --show-ciphers
 
</syntaxhighlight>
 
 
 
Search for: AES-128-CBC, AES-256-CBC
 
 
 
 
 
'''Hash algorithms'''
 
<syntaxhighlight lang="bash">
 
openvpn --show-digests
 
</syntaxhighlight>
 
 
 
Search for: MD5
 
 
 
 
 
'''Handshake algorithms'''
 
<syntaxhighlight lang="bash">
 
openvpn --show-tls
 
</syntaxhighlight>
 
 
 
 
 
 
 
=Server configuration=
 
 
 
See attached file “server.conf”
 
 
 
You can either use TCP or UDP. Performances are the same, UDP is a bit easier to install.
 
 
 
Be careful when you choose the port number!
 
Common open ports:
 
* 80 (http)
 
* 443 (HTTPS)
 
* 8080 (Proxy / JEE servers)
 
 
 
 
 
 
=Firewall=
 
 
 
You can use the following firewall script:
 
 
 
<syntaxhighlight lang="bash">
 
MODPROBE=`which modprobe`
 
IPTABLES=`which iptables`
 
INT_ETH = eth0
 
INT_VPN = tun0
 
IP_LAN_VPN = 10.8.0.0/24
 
 
 
# --- #
 
# VPN #
 
# --- #
 
$MODPROBE iptable_nat
 
 
 
echo " ... Enable NAT features"
 
echo 1 > /proc/sys/net/ipv4/ip_forward
 
 
 
echo " ... Allow all VPN communications (no filter)"
 
$IPTABLES -A INPUT -i $INT_VPN -m state ! --state INVALID -j ACCEPT
 
$IPTABLES -A OUTPUT -o $INT_VPN -m state ! --state INVALID -j ACCEPT
 
 
 
echo " ... Allowing VPN forwarding"
 
# Allow forwarding
 
$IPTABLES -A FORWARD -m state --state RELATED,ESTABLISHED -j ACCEPT
 
$IPTABLES -A FORWARD -i $INT_VPN -s $IP_LAN_VPN -j ACCEPT
 
$IPTABLES -A FORWARD -j REJECT
 
# Allow devices communication $ETH0 <--> tun0
 
$IPTABLES -t nat -A POSTROUTING -s $IP_LAN_VPN -o $INT_ETH -j MASQUERADE
 
# Forward Established, Related
 
$IPTABLES -A FORWARD -s $IP_LAN_VPN -p tcp -m state --state RELATED,ESTABLISHED --sport 1024:65535 --dport 1024:65535 -j ACCEPT
 
$IPTABLES -A FORWARD -s $IP_LAN_VPN -p udp -m state --state RELATED,ESTABLISHED --sport 1024:65535 --dport 1024:65535 -j ACCEPT
 
 
 
Off course, you should also have:
 
echo -e " ... Keep$GREEN ESTABLISHED$BLACK connections "
 
# Keep established connections
 
$IPTABLES -A INPUT -m state --state ESTABLISHED -j ACCEPT
 
$IPTABLES -A OUTPUT -m state --state ESTABLISHED -j ACCEPT
 
 
 
# keep related connections
 
echo -e " ... Keep$GREEN RELATED$BLACK connections"
 
$IPTABLES -A INPUT -m state --state RELATED -j ACCEPT
 
$IPTABLES -A OUTPUT -m state --state RELATED -j ACCEPT
 
</syntaxhighlight>
 
 
 
 
 
 
 
=Startup=
 
 
 
==Restart services==
 
 
 
<syntaxhighlight lang="bash">
 
service openvpn restart
 
service firewall restart
 
</syntaxhighlight>
 
 
 
 
 
==Client Software==
 
 
 
===Linux===
 
 
 
<syntaxhighlight lang="bash">
 
apt-get install openssl openssh-server openvpn
 
</syntaxhighlight>
 
 
 
===Windows===
 
 
 
On windows, many clients are available.
 
The best one for Windows 7 and 8 is: « OpenVPN Connect Client Download for Windows »
 
https://openvpn.net/index.php?option=com_content&id=357
 
 
 
Note: The file must be around 15 Mb.
 
 
 
===MacOSX===
 
The best VPN client is “tunnelblick”
 
http://code.google.com/p/tunnelblick
 
* Configuration files are in ~/librairies/openvpn
 
* That’s the libraries [“bibliothèque”] folder of the current user
 
 
 
 
 
==Client files==
 
 
 
The client requires:
 
* Authority of certification ca.cert
 
* Client private key client.key
 
* Client certificate client.crt
 
 
 
Then, you can setup client configuration.
 
* See “client_conf.ovpn”
 
  
  
'''Notes:'''
 
You have to edit the configuration file.
 
  
* Adjust paths on lines 30-38
 
  
* On Windows you must you the double slash \\
+
=Next steps=
  
* On Linux don’t forget to uncomment the following lines for better security:
 
<syntaxhighlight lang="bash">
 
# Downgrade privileges after initialization (non-Windows only)
 
user nobody
 
group nobody
 
</syntaxhighlight>
 
  
* Linux: depending on your distribution you might need to adjust user / group default name.
+
* [[VPN server]]
 +
* [[VPN client]]

Latest revision as of 17:23, 8 August 2014


VIRTUAL PRIVATE NETWORK (VPN)


Introduction

Reminder: What is a “VPN”?

Nice explanations:

  • English:


As a quick reminder, you can use a VPN for 3 things:

  • Mask your source IP @
VPN change ip address (1)
VPN change ip address (2)


  • Secure communication through the VPN server
VPN client to client


  • Access remote LAN
VPN to LAN


Of course you can combine some / all of these usages.



Sources



Next steps