#  $Id$

Racket -- Ruby Raw Packet library.  

Comments, concerns, bugs, money, food, libations to:

  Jon Hart <[email protected]>

Installation is simple:

  gem install --source http://spoofed.org/files/racket/ racket

Includes support for reading and writing most major layer 2, 3, 4 and
5 protocols.

Basic packet construction and writing is as simple (!) as walking
the stack:

  require 'rubygems'
  require 'racket'

  include Racket
  unless (ARGV.size == 4)
    puts "Usage: #{$0} <srcip> <dstip> <dst_port> <size>"
    exit
  end

  # create a new Racket object and pick an interface
  n = Racket::Racket.new
  n.iface = "eth0"

  # skip right to layer3, layer2 will be done automatically
  # build a new IPv4 layer, and assign src and dst ip from the command line
  n.l3 = IPv4.new
  n.l3.src_ip = ARGV[0]
  n.l3.dst_ip = ARGV[1]
  n.l3.protocol = 0x11

  # tack on UDP 
  n.l4 = UDP.new
  # randomize source port
  n.l4.src_port = 1024 + rand(65535-1024)
  # take destination port from the commandline
  n.l4.dst_port = ARGV[2].to_i
  # build a random amount of garbage for the payload
  n.l4.payload = Misc.randstring(ARGV[3].to_i)

  # fix 'er  up (checksum, length) prior to sending
  n.l4.fix!(n.l3.src_ip, n.l3.dst_ip)

  # off you go
  f = n.sendpacket

  # print out what we built
  n.layers.compact.each do |l|
    puts l.pretty
  end
  puts "Sent #{f}"

Packet reading, done through something like Pcap, is pretty straight forward too:

  require 'rubygems'
  require 'racket'

  # Get the raw capture data from somewhere.  In this case, I've hardcoded it
  binary = "\x45\x10\x00\x3c\x2f\xdf\x40\x00\x40\x06\x89\x17\xc0\xa8\x00\x64\xc0\xa8\x00\x01\x99\xb7\x00\x35\x29\x39\x28\x66\x00\x00\x00\x00\xa0\x02\x16\xd0\xbc\x04\x00\x00\x02\x04\x05\xb4\x04\x02\x08\x0a\x00\x31\x07\xb9\x00\x00\x00\x00\x01\x03\x03\x07"
  i = Racket::IPv4.new(binary)

  # this will print it out all pretty like, and should show a 60 byte TCP packet from 192.168.0.100 to 192.168.0.1
  puts i.pretty