Add 5 of Diamonds build process

resources/flags/linux_flags/5_of_diamonds/make_5_of_diamonds_http_server.rb

@@ -0,0 +1,77 @@
+#!/usr/bin/env ruby
+
+require 'base64'
+
+# source should be PNG file
+source_path = ARGV.shift
+
+if source_path.nil? || source_path.empty? || !File.exists?(source_path)
+  source_path = 'source.png'
+  puts "* No argument provided. Using #{source_path} as the flag."
+end
+
+str = Base64.strict_encode64(File.read(source_path))
+# Because Crystal crashes when concatenating the long Base64 string one byte at a time,
+# we need to make the operation small. We do this by preserving the first 99.9% of the string,
+# and then we obfuscate the rest, which should be enough of a pain to reverse for
+# most people.
+max_size = (str.length * 0.999).to_i
+puts "* First portion of the Base64 string size is: #{max_size}"
+str1 = str[0, max_size]
+str2 = str[max_size..-1]
+puts "* The last #{str2.length} will be obfuscated"
+obfuscated_str = str2.split('').map { |c| %Q|"#{c}"| } * " + "
+
+crystal_code = %Q|
+# This file needs to be compiled into a binary using 'crystal build flag.rb' on a
+# x86/64 Ubuntu machine.
+#
+# The resulting binary will be what is added to the system.
+# It is intended to be accessed after initiating the correct port knocking sequence.
+#
+# To run: ./flag1 -p <port>
+# Defaults to 8989 if no port specified.
+
+require "http/server"
+require "option_parser"
+require "base64"
+
+flag = "#{str1}" + #{obfuscated_str}
+port = 8989
+
+OptionParser.parse! do \|parser\|
+  parser.banner = "Usage: flag_server [arguments]"
+  parser.on("-p", "--port=PORT", "Use a custom port. Default is 8989.") { \|p\| port = p.to_i }
+  parser.on("-h", "--help", "Show this help.") { puts parser }
+end
+
+server = HTTP::Server.new(port) do \|context\|
+  context.response.content_type = "image/png"
+  context.response.print Base64.decode_string("\#{flag}")
+end
+
+puts "Listening on http://127.0.0.1:\#{port}"
+server.listen|
+
+puts "* This is the Crystal code you are about to compile:"
+puts
+puts crystal_code
+puts
+
+CRYSTALFNAME = '/tmp/five_of_diamonds.cr'
+CRYSTALOUTPUT = 'five_of_diamonds'
+
+File.open(CRYSTALFNAME, 'wb') { |f| f.write(crystal_code) }
+
+puts "* Compiling code, please wait..."
+`crystal build --no-debug #{CRYSTALFNAME}`
+
+unless File.exists?(CRYSTALOUTPUT)
+  puts "[x] Crystal failed to build our code"
+  exit
+end
+
+puts "* Crystal built: #{CRYSTALOUTPUT}"
+print '* '
+puts `file #{CRYSTALOUTPUT}`
+