Free freeswan software for linux

Arnos IPTABLES firewall script was initially written because I needed to protect my single-homed Linux machine at work. I wrote it at the time I couldnt find any script that really satisfied my needs except for one that was written by a guy called Seven.
I helped him for several months with the work on his script by suppling patches, reporting bugs etc. In this period I was fortunately also able to master scripting for iptables myself because soon Seven discontinued his work, I never got to even talk to the guy ever again. At that point I decided to continue his work, or actually I started my own branch based on his script.
In the summer of 2002 I finally got an ADSL connection at home. Initially I used the iptables firewall that came with the great ADSL4LINUX-package (http://www.adsl4linux.nl). But it didnt take me long to come to the conclusion that their iptables firewall lacked important features like port-forwarding and flexbility with "trusted hosts" etc.
I also didnt like the fact that I had to use a different firewall for my home machine and the machine at work. This made me decide to use some of the ADSL4LINUX knowledge to implement ADSL support.
By now (about 1 year later as of writing) there are only few remnants left of Sevens original script and many, many, many improvements were applied. One major improvement is the ADSL and NAT support (Check the features page with the specifiations of my firewall). For version 2 (alpha) I plan to completely rewrite to script to make it more flexible and to increase the usability for others.
Main features:
- Very secure stateful filtering firewall
- Both kernel 2.4 & 2.6 support
- It can be used for both single- and multi(eg. dual)-homed boxes
- Masquerading (NAT) and SNAT support
- Multiple external (internet) interfaces
- Support multiroute NAT & SNAT (load balancing over multiple (internet) interfaces)
- Port forwarding (NAT)
- Support MAC address filtering
- Support for DSL/ADSL modems
- Support for PPPoE, PPPoA and bridging modem setups
- Support for static and ISP assigned (DHCP) IPs
- Support for (transparent) proxies
- Full support for DMZs and DMZ-2-LAN forwarding. You can also use it to isolate your eg. wireless LAN.
- (Nmap)(stealth) portscan detection
- Protection against SYN-flooding (DoS attacks)
- Protection against ICMP-flooding (DoS attacks)
- Extensive user-definable logging with rate limiting to prevent log flooding
- Includes options to optimize your throughput
- User definable open ports, closed ports, trusted hosts, blocked hosts etc.
- Log & protection options are both highly customizable
- Support for custom iptables rules in a seperate file
- It can be used with chkconfig runlevel system (eg. RedHat/Fedora)
- Main focus on TCP/UDP/ICMP but additional support for *ALL* IP protocols
- It works with Freeswan IPSEC (VPN) & SSH Sentinel (http://www.freeswan.org) (+virtual IPs)
- It works with PoPTop PPTP (http://www.poptop.org)
- It works with UPnP
- DRDOS protection/detection (experimental)
- Its easy to configure
- And much more.
Enhancements:
- This release fixes a nasty bug in the NAT forwarding rules that caused using subnet-source-restrictions not to work.
- It adds an extra rule to the DHCP server section to allow packets from DHCP servers in the same segment.
- There are several plugin updates.
- A Racoon IPSEC VPN plugin and a transparent DNAT plugin have been added.

seppl is both a protocol definition and a software implementation of a new encryption layer for IPv4. seppl project makes use of symmetric cryptography for encrypting the whole traffic on a network. Its implementation is designed around Linux netfilter/iptables.
seppl introduces two new netfilter targets: CRYPT and DECRYPT. A firewall rule may thus be used for encrypting/decrypting the incoming and outgoing network traffic. This makes seppl extraordinarily easy to use, since no daemons need to run for secure communication.
seppl uses the encryption engine of the Linux Cryptographic API which is available in kernel 2.4.22 and newer.
seppl is primarily intended for encrypting wireless LANs (as secure replacement of the broken WEP encryption) and local ethernet networks but may be used for large scale VPN solutions as well.
The protocol seppl relies on is not compatible with any other software. The protocol is open and well defined but there is no implementation other than this reference software.
Why SEPPL, there are already IPSEC, CIPE,...?
CIPE may be used for point-to-point connections only. It has tunnel structure and thus introduces new IP addresses. This is not always desirable. It requires a user space daemon.
IPSEC/FreeSwan is extremely complicated to use. Due to its strange routing scheme it is nearly impossible to use together with routing daemons. IPSEC is heavyweight.
seppl is truely peer-to-peer. It encrypts seamlessly all outgoing traffic and it thus compatible with routing daemons. It is extremely easy to use as well, as it makes no change to the normal routing behaviour. seppl is extremely lightweight.
The Implementation
The implementation consists of three Linux kernel modules: seppl.o, ipt_CRYPT.o and ipt_DECRYPT.o. The former is the in-kernel key manager, the latter are the two new netfilter targets. Both depend on seppl.o.
seppl.o must be inserted into kernel in first place. The key manager may be accessed with the file /proc/net/seppl_keyring. It contains binary key data, and is initially empty. You may add a new key by writing it to that file.
The two Python scripts seppl-ls and seppl-gen-key me be used for key management. seppl-ls may be used for converting seppl keys between the binary format used by /proc/net/seppl_keyring and a human readable XML based format. Simply call seppl-ls for a list of all currently active keys. seppl-gen-key generates a new key from /dev/urandom. By default it will use the XML format. The parameter -x forces binary mode. You may generate and activate two keys "linus" and "alan" by issuing the following command lines:
seppl-gen-key -n linus -x > /proc/net/seppl_keyring
seppl-gen-key -n alan -x > /proc/net/seppl_keyring
seppl-ls without argument lists the new keys saved in the kernel keyring. You may remove all (currently unused) keys by issuing:
echo clear > /proc/net/seppl_keyring
Since seppl is based on symmetric cryptography using shared keys you have to copy newly generated keys to every host you want to connect to your seppl infrastructure. (preferably via SSH or any other secure file transfer) You get a binary copy of your current keyring by issuing:
cat /proc/net/seppl_keyring > keyring.save
Now copy that file keyring.save to all other hosts and issue the following command there:
cat keyring.save > /proc/net/seppl_keyring
That is simple, isnt it?
After doing so you may configure your firewall settings on each host:
iptables -t mangle -A POSTROUTING -o eth0 -j CRYPT --key linus
iptables -t mangle -A PREROUTING -i eth0 -j DECRYPT
This will encrypt all outgoing traffic on eth0 with the key "linus". All incoming traffic is decrypted with either "linus" or "alan", depending on the key name specified in the specific network packet. Unencrypted incoming packets are silently dropped. Use
iptables -t mangle -A PREROUTING -p 177 -i eth0 -j DECRYPT
for allowing both crypted and unencrypted incoming traffic.
Thats it. Youre done. All your traffic on the local subnet is now crypted with seppl.
The default cipher is AES-128. If you dont specify the name of the used key it defaults to "def".
An SysV init script /etc/init.d/seppl is provided. It will load seppls kernel modules and write all keys from the directory /etc/seppl to the kernel keyring. It will not add any firewall rules, however.
Performance issues
The network packets are increased in size when they are crypted, since two new headers and the IV are added. (36 bytes in average) This conflicts on some way with the MTU management of the Linux kernel and results in having all large packets (that is: package size near MTU) fragmented in one large and another very small package. This will hurt network performance. A work-around of this limitation is using the TCPMSS target of netfilter to adjust the MSS value in the TCP header to smaller values. This will increase TCP perfomance, since TCP packets of the size of the MTU are no longer generated. Thus no fragmentation is needed. However, TCPMSS is TCP specific, it wont help on UDP or other IP protocols.
Add the following line before encryption to your firewall setup:
iptables -t mangle -A POSTROUTING -p tcp --tcp-flags SYN,RST SYN -o eth0 -j TCPMSS --set-mss $((1500-40-8-16-6-15))
The Protocol
For encryption every single unencrypted packet is taken and converted to a crypted one. Not a single further packet is ever sent.
Original SEPPL counterpart
+------------+ +-----------------------+
| IP-Header | | Modified IP-Header | |
+------------+ +-----------------------+ |
| Payload | | SEPPL-Header | > Unencrypted
+------------+ +-----------------------+ |
| Initialization Vector | |
+-----------------------+ /
| SEPPL-Header |
+-----------------------+ | Crypted
| Payload | |
+-----------------------+ /
The original IP header is kept as far as possible. Only three fields are replaced with new values. The protocol number is set to 177, the fragment offset is set to 0 and the total length is corrected to the new length. All other fields are kept as is, including IP options.
The unencrypted seppl header consists of a one-byte cipher number and a key name. Currently only 0 and 1 are defined as cipher numbers for AES with 128bit key, resp. AES with 192bit key. The key name (7 bytes) may be used to select a specific key in a larger keyring.
The IV is used for CBC coding of the cipher used. It differs from packet to packet, but is not randomly generated. Due to perfomance reasons, only the initial IV on system startup is randomized, all following IVs are generated by incrementing the previous ones.
The crypted seppl header consists of three saved fields of the original IP header (protocol number, fragment offset, total length) and a byte which is always 0 for detecting unmatching keys.
The payload is the original IP-playload, from the TCP/UDP/other header to the end.
Version restrictions:
- seppl interferes with netfilters connection tracking in some way. Thus you will not be able to use NAT in conjunction with seppl. If you use connection tracking in some other way together with seppl your mileage may vary.
- seppl is tested with Linux 2.6.1. Use version 0.3 for Linux 2.4.