metasploit-framework/modules/encoders/x86/call4_dword_xor.rb

require 'msf/core'

module Msf
module Encoders
module X86

class Call4Dword < Msf::Encoder::Xor

	def initialize
		super(
			'Name'             => 'Call+4 Dword XOR Encoder',
			'Version'          => '$Revision$',
			'Description'      => 'Call+4 Dword XOR Encoder',
			'Author'           => [ 'hdm', 'spoonm' ],
			'Arch'             => ARCH_X86,
			'License'          => MSF_LICENSE,
			'Decoder'          =>
				{
					'KeySize'    => 4,
					'BlockSize'  => 4,
				})
	end

	#
	# Returns the decoder stub that is adjusted for the size of
	# the buffer being encoded
	#
	def decoder_stub(state)
		decoder = 
			Rex::Arch::X86.sub(-(((state.buf.length - 1) / 4) + 1), Rex::Arch::X86::ECX,
				state.badchars) +
			"\xe8\xff\xff\xff" + # call $+4
			"\xff\xc0"         + # inc eax
			"\x5e"             + # pop esi
			"\x81\x76\x0eXORK" + # xor [esi + 0xe], xork
			"\x83\xee\xfc"     + # sub esi, -4
			"\xe2\xf4"           # loop xor

		# Calculate the offset to the XOR key
		state.decoder_key_offset = decoder.index('XORK')

		return decoder
	end

end

end end end