This page will get you started using Linux FreeS/WAN with opportunistic encryption (OE). OE enables you to set up IPsec tunnels to a site without co-ordinating with the site administrator, and without hand configuring each tunnel. If enough sites support OE, a "FAX effect" occurs, and many of us can communicate without eavesdroppers.
Opportunistic encryption is new technology and we are still working out some fine points. Please see this list of known issues.
To set up opportunistic encryption, you will need:
Note: Only Linux FreeS/WAN supports opportunistic encryption.
Our instructions are for a recent Red Hat with a stock Red Hat kernel. For other ways to install, see our install document.
Check your kernel version with
uname -a
From our FTP site, get the kernel module which matches your kernel. For example:
freeswan-module-1.99_2.4.18_3-0.i386.rpm
Note: Our kernel modules will only work on the Red Hat kernel they were built for, since they are very sensitive to small changes in the kernel.
Get FreeS/WAN utilities to match. For example:
freeswan-1.99_2.4.18_3-0.i386.rpm
While you're at our ftp site, grab the RPM signing key
freeswan-rpmsign.asc
If you're running RedHat 8.x, import this key into the RPM database:
rpm --import freeswan-rpmsign.asc
For RedHat 7.x systems, you'll need to add it to your PGP keyring:
pgp -ka freeswan-rpmsign.asc
Check the signatures on both RPMs using:
rpm --checksig freeswan-module-1.99_2.4.18_3-0.i386.rpm rpm --checksig freeswan-1.99_2.4.18_3-0.i386.rpm
You should see:
freeswan-module-1.99_2.4.18_3-0.i386.rpm: pgp md5 OK freeswan-1.99_2.4.18_3-0.i386.rpm: pgp md5 OK
Become root:
su
Install your RPMs with:
rpm -ivh freeswan-module-1.99_2.4.18_3-0.i386.rpm
rpm -ivh freeswan-1.99_2.4.18_3-0.i386.rpm
Then, start FreeS/WAN:
service ipsec start
To check that you have a successful install, run:
ipsec verify
You should see at least:
Checking your system to see if IPsec got installed and started correctly Version check and ipsec on-path [OK] Checking for KLIPS support in kernel [OK] Checking for RSA private key (/etc/ipsec.secrets) [OK] Checking that pluto is running [OK]
If any of these first four checks fails, see our troubleshooting guide.
Determine the fullest form of opportunism your system can support.
When you set yourself up as an opportunistic initiator:
Find a DNS forward domain where you can publish your key. You'll need access to the DNS zone files for that domain. For the following examples, we'll use "example.com".
Dynamic IP users take note: the domain where you place your key need not be associated with the IP address for your system, or even with your system's usual hostname.
Choose a name within that domain which you will use to identify your machine. Normally, but not always, your ID is the same as your machine name. Our machine is called xy, and we'll choose the corresponding FQDN xy.example.com.
Generate a DNS KEY record containing your system's public key with the command:
ipsec showhostkey
This command takes the contents of /etc/ipsec.secrets and reformats it into something usable by ISC's BIND. The result should look like this (with the key data trimmed down for clarity):
; RSA 2048 bits xy.example.com Sat Apr 15 13:53:22 2000 xy.example.com. IN KEY 0x4200 4 1 AQOF8tZ2...+buFuFn/
Change xy.example.com to your FQDN.
Insert the record into DNS, or have a system adminstrator do it for you. It may take up to 48 hours for the record to propagate, but it's usually much quicker.
Check your DNS work
ipsec verify
You ought to see something like:
Looking for forward key for xy.example.com [OK]
For this type of opportunism, only the forward key test is relevant.
If your FreeS/WAN is older than 1.98b, simply query your nameserver (here, 1.2.3.254):
dig @1.2.3.254 xy.example.com KEY
You should see (with the key again shortened):
;; ANSWER SECTION: xy.example.com. 6835 IN KEY 16896 4 1 AQO6DJc6LIwGq82ehvIGLKn4S...
In /etc/ipsec.conf find conn me-to-anyone
Make it look like:
conn me-to-anyone left=%defaultroute leftrsasigkey=%dnsondemand right=%opportunistic rightrsasigkey=%dnsondemand keylife=1h rekey=no leftid=@xy.example.com # put your ID here auto=route # be sure this is enabled
Put your FQDN ID, preceded by an @sign, in place of @xy.example.com. Be sure auto=route is enabled.
Restart FreeS/WAN so that the new configuration takes effect:
service ipsec restart
That's it! Test your connection.
This allows you to initiate and receive opportunistic connections from one machine.
Generate a KEY record:
ipsec showhostkey
This command takes the contents of /etc/ipsec.secrets and reformats it into something usable by ISC's BIND. It will yield (with key data trimmed for clarity):
; RSA 2048 bits xy.example.com Sat Apr 15 13:53:22 2000 xy.example.com IN KEY 0x4200 4 1 AQOF8tZ2...+buFuFn/
Edit it to insert the IP address in reverse map format. In our example, 1.2.3.4 becomes 4.3.2.1.in-addr.arpa. The result:
; RSA 2048 bits xy.example.com Sat Apr 15 13:53:22 2000 4.3.2.1.in-addr.arpa. IN KEY 0x4200 4 1 AQOF8tZ2...+buFuFn/
This lets others know that this machine can receive opportunistic connections. It also lets them know that the machine is authorized to encrypt on its own behalf.
Use the command:
ipsec showhostkey --txt 1.2.3.4
where you replace 1.2.3.4 with your public IP.
The record (with key shortened) looks like:
; RSA 2048 bits xy.example.com Sat Apr 15 13:53:22 2000 IN TXT "X-IPsec-Server(10)=1.2.3.4" " AQOF8tZ2...+buFuFn/"
Send these records to your ISP, to be published in your IP's reverse map. It may take up to 48 hours for these to propagate, but usually takes much less time.
Test that your KEY has been published by querying your nameserver (here, 1.2.3.254):
dig @1.2.3.254 4.3.2.1.in-addr.arpa. KEY
You should see (with the key shortened for clarity):
;; ANSWER SECTION: xy.example.com. 6835 IN KEY 16896 4 1 AQO6DJc6LIwGq82ehvIGLKn4S...
Next, test that your TXT record is visible:
dig @1.2.3.254 4.3.2.1.in-addr.arpa. TXT
You should see (with the key shortened for clarity):
;; ANSWER SECTION: xy.example.com. 6835 IN KEY 16896 4 1 AQO6DJc6LIwGq82ehvIGLKn4S...
Find conn me-to-anyone in /etc/ipsec.conf:
Adjust it to look like:
conn me-to-anyone left=%defaultroute leftrsasigkey=%dnsondemand right=%opportunistic rightrsasigkey=%dnsondemand keylife=1h rekey=no auto=route # be sure this is enabled # Note there is NO leftid=
If you've previously configured for initiator-only opportunism, remove leftid=
#leftid=xy.example.com
Restart FreeS/WAN so that it reads the new settings:
service ipsec restart
If you are running a default install of RedHat 8.0, take note: you will need to alter your iptables rule setup to allow IPSec traffic through your firewall. See our firewall document for sample rules you can add to /etc/sysconfig/iptables to permit this.
More information.That's it. Now, test your connection.
You need these so that your Opportunistic peers can:
On the gateway, generate a TXT record with:
ipsec showhostkey --txt 1.2.3.4
Use your gateway address in place of 1.2.3.4
You should see (keys are trimmed for clarity throughout our example):
; RSA 2048 bits gateway.example.com Sat Apr 15 13:53:22 2000 IN TXT "X-IPsec-Server(10)=1.2.3.4" " AQOF8tZ2...+buFuFn/"
This MUST BE the same key as in your gateway's KEY record, or nothing will work.
In a text file, make one copy of this TXT record for each subnet node:
; RSA 2048 bits gateway.example.com Sat Apr 15 13:53:22 2000 IN TXT "X-IPsec-Server(10)=1.2.3.4" " AQOF8tZ2...+buFuFn/" ; RSA 2048 bits gateway.example.com Sat Apr 15 13:53:22 2000 IN TXT "X-IPsec-Server(10)=1.2.3.4" " AQOF8tZ2...+buFuFn/" ; RSA 2048 bits gateway.example.com Sat Apr 15 13:53:22 2000 IN TXT "X-IPsec-Server(10)=1.2.3.4" " AQOF8tZ2...+buFuFn/"
Above each entry, insert a line like this:
1.42.42.42.in-addr.arpa. IN PTR arthur.example.com
It must include:
The result will be a file full of TXT records, like this:
1.42.42.42.in-addr.arpa. IN PTR arthur.example.com ; RSA 2048 bits gateway.example.com Sat Apr 15 13:53:22 2000 IN TXT "X-IPsec-Server(10)=1.2.3.4" " AQOF8tZ2...+buFuFn/" 2.42.42.42.in-addr.arpa. IN PTR ford.example.com ; RSA 2048 bits gateway.example.com Sat Apr 15 13:53:22 2000 IN TXT "X-IPsec-Server(10)=1.2.3.4" " AQOF8tZ2...+buFuFn/" 3.42.42.42.in-addr.arpa. IN PTR trillian.example.com ; RSA 2048 bits gateway.example.com Sat Apr 15 13:53:22 2000 IN TXT "X-IPsec-Server(10)=1.2.3.4" " AQOF8tZ2...+buFuFn/"
Ask your ISP to publish these records in your reverse map.
Check a couple of records with commands like this one:
dig @1.2.3.254 1.42.42.42.in-addr.arpa. TXT
Replace 1.2.3.254 with your nameserver's IP, and 1.42.42.42.in-addr.arpa. with the reverse-format IP of one of your subnet nodes.
You should see:
ANSWER SECTION: 1.42.42.42.in-addr.arpa. 180 IN TXT "X-IPsec-Server(10)=1.2.3.4 " AQOF8tZ2...+buFuFn/"
In /etc/ipsec.conf place this before me-to-anyone :
conn subnet-to-anyone also=me-to-anyone leftsubnet=42.42.42.0/24More detail.
Once again, restart FreeS/WAN to complete the configuration changes:
service ipsec restart
Proceed to the next section and test away.
The quick method is:
links oetest.freeswan.org
A thought for the paranoid -- the feds are probably watching that site. You should see:
You seem to be connecting from: 1.2.3.4 which DNS says is: xy.example.com _________________________________________________________________ Status E-route OE enabled 16 192.139.46.73/32 -> 1.2.3.4/32 => tun0x2097@1.2.3.5 OE enabled 176 192.139.46.77/32 -> 1.2.3.4/32 => tun0x208a@1.2.3.5
If you do not see this, see this section of the FAQ.
Congratulations! Your machine will now encrypt whenever it can.
If you haven't already, read up on our known issues, below. Or, proceed to make some vpn connections.