OpenVPN(EN)

As a user-space VPN daemon, OpenVPN is compatible with with SSL/TLS, RSA Certificates and X509 PKI, NAT, DHCP, and TUN/TAP virtual devices.

OpenVPN is not compatible with IPSec, IKE, PPTP, or L2TP.

Installation

Download source from openvpn.net

Download verison 2.0

install Lzo

tar zxvf lzo-1.08.tar.gz
cd lzo-1-08.tar.gz
./configure --prefix=/usr
make ; make install-strip

install OpenVPN

tar zxvf openvpn-2.0.tar.gz
cd openvpn-2.0
./configure --prefix=/usr \
--sysconfdir=/etc/openvpn \
--enable-pthread \
--enable-iproute2 \
--with-ssl \
--with-lzo-header=/usr/include \
--with-lzo-lib=/usr/lib \
--with-ifconfig \
--with-route \
--with-mem-check=dmalloc 
make ; make install-strip

Configuring Certificates

Save all certificates in /etc/openvpn/certs

This is a small RSA key management package,
based on the openssl command line tool, that
can be found in the easy-rsa subdirectory
of the OpenVPN distribution.

These are reference notes.  For step
by step instructions, see the HOWTO:

http://openvpn.net/howto.html

INSTALL

1. Edit vars.
2. Set KEY_CONFIG to point to the openssl.cnf file
   included in this distribution.
3. Set KEY_DIR to point to a directory which will
   contain all keys, certificates, etc.  This
   directory need not exist, and if it does,
   it will be deleted with rm -rf, so BE
   CAREFUL how you set KEY_DIR.
4. (Optional) Edit other fields in vars
   per your site data.  You may want to
   increase KEY_SIZE to 2048 if you are
   paranoid and don't mind slower key
   processing, but certainly 1024 is
   fine for testing purposes.  KEY_SIZE
   must be compatible across both peers
   participating in a secure SSL/TLS
   connection.
5  . vars
6. ./clean-all
7. As you create certificates, keys, and
   certificate signing requests, understand that
   only .key files should be kept confidential.
   .crt and .csr files can be sent over insecure
   channels such as plaintext email.
8. You should never need to copy a .key file
   between computers.  Normally each computer
   will have its own certificate/key pair.

BUILD YOUR OWN ROOT CERTIFICATE AUTHORITY (CA) CERTIFICATE/KEY

1. ./build-ca
2. ca.crt and ca.key will be built in your KEY_DIR
   directory

BUILD AN INTERMEDIATE CERTIFICATE AUTHORITY CERTIFICATE/KEY (optional)

1. ./build-inter inter
2. inter.crt and inter.key will be built in your KEY_DIR
   directory and signed with your root certificate.

BUILD DIFFIE-HELLMAN PARAMETERS (necessary for
the server end of a SSL/TLS connection).

1. ./build-dh

BUILD A CERTIFICATE SIGNING REQUEST (If
you want to sign your certificate with a root
certificate controlled by another individual
or organization, or residing on a different machine).

1. Get ca.crt (the root certificate) from your
   certificate authority.  Though this
   transfer can be over an insecure channel, to prevent
   man-in-the-middle attacks you must confirm that
   ca.crt was not tampered with.  Large CAs solve this
   problem by hardwiring their root certificates into
   popular web browsers.  A simple way to verify a root
   CA is to call the issuer on the telephone and confirm
   that the md5sum or sha1sum signatures on the ca.crt
   files match (such as with the command: "md5sum ca.crt").
2. Choose a name for your certificate such as your computer
   name.  In our example we will use "mycert".
3. ./build-req mycert
4. You can ignore most of the fields, but set
   "Common Name" to something unique such as your
   computer's host name.  Leave all password
   fields blank, unless you want your private key
   to be protected by password.  Using a password
   is not required -- it will make your key more secure
   but also more inconvenient to use, because you will
   need to supply your password anytime the key is used.
   NOTE: if you are using a password, use ./build-req-pass
   instead of ./build-req
5. Your key will be written to $KEY_DIR/mycert.key
6. Your certificate signing request will be written to
   to $KEY_DIR/mycert.csr
7. Email mycert.csr to the individual or organization
   which controls the root certificate.  This can be
   done over an insecure channel.
8. After the .csr file is signed by the root certificate
   authority, you will receive a file mycert.crt
   (your certificate).  Place mycert.crt in your
   KEY_DIR directory.
9. The combined files of mycert.crt, mycert.key,
   and ca.crt can now be used to secure one end of
   an SSL/TLS connection.

SIGN A CERTIFICATE SIGNING REQUEST

1. ./sign-req mycert
2. mycert.crt will be built in your KEY_DIR
   directory using mycert.csr and your root CA
   file as input.

BUILD AND SIGN A CERTIFICATE SIGNING REQUEST
USING A LOCALLY INSTALLED ROOT CERTIFICATE/KEY -- this
script generates and signs a certificate in one step,
but it requires that the generated certificate and private
key files be copied to the destination host over a
secure channel.

1. ./build-key mycert (no password protection)
2. OR ./build-key-pass mycert (with password protection)
3. OR ./build-key-pkcs12 mycert (PKCS #12 format)
4. OR ./build-key-server mycert (with nsCertType=server)
5. mycert.crt and mycert.key will be built in your
   KEY_DIR directory, and mycert.crt will be signed
   by your root CA. If ./build-key-pkcs12 was used a
   mycert.p12 file will also be created including the
   private key, certificate and the ca certificate.

IMPORTANT

To avoid a possible Man-in-the-Middle attack where an authorized
client tries to connect to another client by impersonating the
server, make sure to enforce some kind of server certificate
verification by clients.  There are currently four different ways
of accomplishing this, listed in the order of preference:

(1) Build your server certificates with the build-key-server
    script.  This will designate the certificate as a
    server-only certificate by setting nsCertType=server.
    Now add the following line to your client configuration:

    ns-cert-type server

    This will block clients from connecting to any
    server which lacks the nsCertType=server designation
    in its certificate, even if the certificate has been
    signed by the CA which is cited in the OpenVPN configuration
    file (--ca directive).

(2) Use the --tls-remote directive on the client to
    accept/reject the server connection based on the common
    name of the server certificate.

(3) Use a --tls-verify script or plugin to accept/reject the
    server connection based on a custom test of the server
    certificate's embedded X509 subject details.
IMPORTANT

To avoid a possible Man-in-the-Middle attack where an authorized
client tries to connect to another client by impersonating the
server, make sure to enforce some kind of server certificate
verification by clients.  There are currently four different ways
of accomplishing this, listed in the order of preference:

(1) Build your server certificates with the build-key-server
    script.  This will designate the certificate as a
    server-only certificate by setting nsCertType=server.
    Now add the following line to your client configuration:

    ns-cert-type server

    This will block clients from connecting to any
    server which lacks the nsCertType=server designation
    in its certificate, even if the certificate has been
    signed by the CA which is cited in the OpenVPN configuration
    file (--ca directive).

(2) Use the --tls-remote directive on the client to
    accept/reject the server connection based on the common
    name of the server certificate.

(3) Use a --tls-verify script or plugin to accept/reject the
    server connection based on a custom test of the server
    certificate's embedded X509 subject details.

(4) Sign server certificates with one CA and client certificates
    with a different CA.  The client config "ca" directive should
    reference the server-signing CA while the server config "ca"
    directive should reference the client-signing CA.

NOTES

Show certificate fields:
  openssl x509 -in cert.crt -text

# cd easy-rsa
# vi vars
. vars
./clean-all

## BUILD YOUR OWN ROOT CERTIFICATE AUTHORITY (CA) CERTIFICATE/KEY
./build.ca

## BUILD AN INTERMEDIATE CERTIFICATE AUTHORITY CERTIFICATE/KEY (optional)
./build-inter inter

## BUILD DIFFIE-HELLMAN PARAMETERS (necessary for the server end of a SSL/TLS connection).
./build.dh

## BUILD A CERTIFICATE SIGNING REQUEST 
## (If you want to sign your certificate with a root certificate controlled by another individual 
## or organization, or residing on a different machine)

./build-req mycert
## SIGN A CERTIFICATE SIGNING REQUEST
./sign-req mycert

## BUILD AND SIGN A CERTIFICATE SIGNING REQUEST USING A LOCALLY INSTALLED ROOT CERTIFICATE/KEY
./build-key mycert (no password protection)
OR 
./build-key-pass mycert (with password protection)
OR 
./build-key-pkcs12 mycert (PKCS #12 format)
OR 
./build-key-server mycert (with nsCertType=server)

Configuring the Server

Edit the server.conf file: vi /etc/openvpn/server.conf

## Mode Server
mode server

## Local Host Name/IP Server
;local 127.0.0.1

## Protocol
;proto tcp
proto udp

## Port
; port 1194

## Device Interface
;dev tap
dev tun

## TAP-Win32 adapter name
;dev-node MyTap

## SSL/TLS 
## root certificate (ca)
## certificate (cert)
## private key (key)
ca /etc/openvpn/certs/ca.crt
cert /etc/openvpn/certs/server.crt
key /etc/openvpn/certs/server.key

## Diffie hellman parameters
dh dh1024.pem

## VPN subnet
server 10.8.0.0 255.255.255.0

ifconfig-pool-persist ipp.txt

##ethernet bridging
;server-bridge 10.8.0.4 255.255.255.0 10.8.0.50 10.8.0.100

## dhcpcaveats
;push "route 192.168.10.0 255.255.255.0"
;push "route 192.168.20.0 255.255.255.0"

;client-config-dir ccd

;route 192.168.40.128 255.255.255.248

;client-config-dir ccd

;route 10.9.0.0 255.255.255.252

;learn-address ./script

## dhcpcaveats
;push "redirect-gateway"
;push "dhcp-option DNS 10.8.0.1"
;push "dhcp-option WINS 10.8.0.1"

##
;client-to-client

## same "COMMON NAME" certificate/key
;duplicate-cn

## Status Connection
keepalive 10 120

## tls-auth key
;tls-auth ta.key 0 

## Cryptographic cipher
;cipher BF-CBC        # Blowfish (default)
;cipher AES-128-CBC   # AES
;cipher DES-EDE3-CBC  # Triple-DES

## Link Compresion
comp-lzo

## Max Client Connections
;max-clients 100

## daemon privileges (non windows saja)
user nobody
group nobody

persist-key
persist-tun

## Openvpn Log
;log         /var/log/openvpn/openvpn.log
;log-append  /var/log/openvpn/openvpn.log

## Output Log
status /var/log/openvpn/openvpn-status.log

## Log 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

## Repeating Messages
;mute 20

## Pid File
writepid /var/run/openvpn.pid

Routing

echo 1 > /proc/sys/net/ipv4/ip_forward
route add -net 10.0.1.0 netmask 255.255.255.0 gw 10.4.0.2

Firewall

iptables -A INPUT -p udp -s 1.2.3.4 --dport 1194 -j ACCEPT
OR
iptables -A INPUT -p udp --dport 1194 -j ACCEPT

## Tun Device
iptables -A INPUT -i tun+ -j ACCEPT
iptables -A FORWARD -i tun+ -j ACCEPT

## Tap Device
iptables -A INPUT -i tap+ -j ACCEPT
iptables -A FORWARD -i tap+ -j ACCEPT

Configuring the Client

Edit the client.conf file: vi /etc/openvpn/client.conf

## Config
client

## Device Interface
;dev tap
dev tun

## Tap adapter name (Win only)
;dev-node MyTap

## Conectivity
;proto tcp
proto udp

## Server [hostname/ip] [port]
remote my-server-1 1194
;remote my-server-2 1194

## load-balancing
;remote-random

## resolve host name OpenVPN server
resolv-retry infinite

# local port
nobind

## privileges (non windows saja)
user nobody
group nobody

## preserve
persist-key
persist-tun

## HTTP proxy
;http-proxy-retry 
;http-proxy [proxy server] [proxy port]

## duplicate packet warnings
;mute-replay-warnings

## SSL/TLS parms
/etc/openvpn/certs/ca ca.crt
/etc/openvpn/certs/cert client.crt
/etc/openvpn/certs/key client.key

## nsCertType key
;ns-cert-type server

## tls-auth key
;tls-auth /etc/openvpn/certs/ta.key 1

## Cryptographic cipher
;cipher x

## Link compression
comp-lzo

## 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

## repeating messages
;mute 20

Routing

route add -net 10.0.0.0 netmask 255.255.255.0 gw 10.4.0.1 

Example

Example 1: A simple tunnel without security
On May: Server Side

openvpn --remote jun.kg --dev tun1 --ifconfig 10.4.0.1 10.4.0.2 --verb 9

On Jun: Client Side

openvpn --remote may.kg --dev tun1 --ifconfig 10.4.0.2 10.4.0.1 --verb 9 

On May:

   ping 10.4.0.2 

On Jun:

   ping 10.4.0.1

Example 2: A tunnel with static-key security (i.e. using a pre-shared secret)
On May: Server Side

openvpn --remote jun.kg --dev tun1 --ifconfig 10.4.0.1 10.4.0.2 \
--verb 5 --secret key

On Jun: Client Side

openvpn --remote may.kg --dev tun1 --ifconfig 10.4.0.2 10.4.0.1 \
--verb 5 --secret key 

On May:

   ping 10.4.0.2 

On Jun:

   ping 10.4.0.1

Example 3: A tunnel with full TLS-based security
On May: Server Side

openvpn --remote jun.kg --dev tun1 --ifconfig 10.4.0.1 10.4.0.2 \
--tls-client --ca tmp-ca.crt --cert client.crt --key client.key \
--reneg-sec 60 --verb 5 

On Jun: Client Side

openvpn --remote may.kg --dev tun1 --ifconfig 10.4.0.2 10.4.0.1 \
--tls-server --ca tmp-ca.crt --cert server.crt --key server.key \
--reneg-sec 60 --verb 5 --dh dh1024.pem

On May:

   ping 10.4.0.2 

On Jun:

   ping 10.4.0.1

External Links

• http://dmalloc.com/
• http://valgrind.org/
• http://www.oberhumer.com/opensource/lzo/
• http://openvpn.net/
• http://openvpn.net/howto.html
• http://openvpn.net/1xhowto.html (Old-v1.06)
• http://openvpn.net/man.html