Add script to unsign Mac executables

unsign

@@ -0,0 +1,99 @@
+#!/usr/bin/env ruby
+# Deactivates any embedded code signatures in a Mach-O binary.
+
+module MachO
+  class Unsign
+    def self.unsign(filename)
+      File.open(filename, "r+") do |f|
+        Unsign.new(f).headers
+      end
+    end
+
+    attr_accessor :headers
+
+    protected
+
+    FatHeader = Struct.new(:cpu_type, :cpu_subtype, :offset, :size, :align, :mach)
+    MachHeader = Struct.new(:cpu_type, :cpu_subtype, :filetype, :ncmds, :sizeofcmds, :flags, :reserved, :cmds)
+    LoadCommand = Struct.new(:cmd, :cmdsize)
+
+    def initialize(f)
+      @f = f
+      @headers = process
+    end
+
+    def debug(message)
+      puts message if ENV["DEBUG"]
+    end
+
+    def word_type
+      @big_endian ? 'N' : 'V'
+    end
+
+    def patch_code_signature(lc)
+      # just change LC_CODE_SIGNATURE to a high value that will be ignored by the loader
+      debug "PATCHING LC_CODE_SIGNATURE"
+      @f.seek(-8, IO::SEEK_CUR)
+      @f.write([0xff, lc.cmdsize].pack("#{word_type}2"))
+      lc
+    end
+
+    def process_mach
+      len = @x86_64 ? 7 : 6
+      header = MachHeader.new(*@f.read(len*4).unpack("#{word_type}#{len}"))
+      debug "MACH HEADER: #{header.inspect}"
+      header.cmds = (1..(header.ncmds)).collect do
+        lc = LoadCommand.new(*@f.read(8).unpack("#{word_type}2"))
+        debug "LOAD COMMAND: #{lc.inspect}"
+
+        lc = case lc.cmd
+        when 0x1d then patch_code_signature(lc)
+        else lc
+        end
+
+        @f.seek(lc.cmdsize - 8, IO::SEEK_CUR)
+
+        lc
+      end
+      header
+    end
+
+    def process_fat
+      num_arches, = @f.read(4).unpack("N")
+      arches = (1..num_arches).collect do
+        FatHeader.new(*@f.read(20).unpack("N5"))
+      end
+      debug "FAT HEADER: #{arches.inspect}"
+      arches.each do |arch|
+        @f.seek(arch.offset)
+        arch.mach = process
+      end
+      arches
+    end
+
+    def process
+      magic, = @f.read(4).unpack("N")
+      debug "MAGIC: 0x%08x" % magic
+      case magic
+      when 0xcafebabe then @big_endian, @x86_64 = false, false; process_fat
+      when 0xfeedface then @big_endian, @x86_64 = true,  false; process_mach
+      when 0xcffaedfe then @big_endian, @x86_64 = false, true;  process_mach
+      when 0xcefaedfe then @big_endian, @x86_64 = false, false; process_mach
+      else raise "unknown magic: 0x%08x" % magic
+      end
+    end
+  end
+end
+
+# command line driver
+if __FILE__ == $0
+  if ARGV.empty?
+    $stderr.puts "usage:  #{$0} filename ..."
+    exit 1
+  end
+
+  ARGV.each do |filename|
+    puts "removing signatures from: #{filename}"
+    MachO::Unsign::unsign(filename)
+  end
+end