jamesduncombe · July 1, 2014 20:47 · Jul 1, 2014 · Jul 1, 2014
diff --git a/gistfile1.rb → jpeg_smash.rb b/gistfile1.rb → jpeg_smash.rb
diff --git a/gistfile1.rb b/gistfile1.rb
@@ -0,0 +1,62 @@
+#!/usr/bin/env ruby
+require 'optparse'
+
+options = {}
+
+# Markers
+JPEG_START = 'ffda'
+JPEG_END = 'ffd9'
+
+OptionParser.new do |opts|
+  opts.banner = 'Usage: jpeg_crush.rb [options]'
+
+  opts.on('-f', '--file [FILE]', 'Use source file') do |v|
+    options[:file] = v
+  end
+
+  opts.on('-o', '--output-file [FILE]', 'Use output file') do |v|
+    options[:output_file] = v
+  end
+
+  opts.on('-m', '--message [MESSAGE]', 'Specify message to inject') do |v|
+    options[:message] = v.unpack("H*").first.scan(/.{2}/)
+  end
+end.parse!
+
+puts 'Opening source file...'
+if File.exists? options[:file]
+  original = File.binread(options[:file])
+else
+  raise ArgumentError, 'Incorrect filename given'
+end
+
+puts 'Unpacking hex into pairs...'
+ready = original.unpack('H*').first.scan(/.{2}/)  # get hex pairs
+
+def start_of_data(data)
+  data.each_with_index { |e,i| return i if e == 'ff' && data[i+1] == 'da' }
+end
+
+def end_of_data(data)
+  data.each_with_index { |e,i| return i if e == 'ff' && data[i+1] == 'd9' }
+end
+
+# remember these are split into 2's and there's 4 as delimeters (ffda and ffd9) hance
+# the 2 offset forwards and back (we don't want to ovewrite the markers)
+puts 'Getting offsets for JPEG markers...'
+starts = start_of_data(ready) + 2
+ends = end_of_data(ready) - 2
+
+puts 'Get the length of my name, insert Hex randomly...'
+options[:message].count.times do |t|
+  loc = rand(starts+2..ends-2)
+  ready[loc] = options[:message].shuffle.first
+end
+
+# re-assemble file for writing out to a JPEG file
+ready = [ready.join].pack('H*')
+
+f = File.open(options[:output_file], 'w+')
+f.write ready
+f.close
+puts 'Done :)'