#!/usr/bin/env ruby require 'rex/text' module Rex module Encoder module Alpha2 class Generic @@default_accepted_chars = ('a' .. 'z').to_a + ('B' .. 'Z').to_a + ('0' .. '9').to_a def Generic.gen_decoder_prefix(reg, offset) # Should never happen - have to pick a specifc # encoding: # alphamixed, alphaupper, unicodemixed, unicodeupper '' end def Generic.gen_decoder(reg, offset) # same as above return '' end def Generic.gen_base_set(ignored_max=0x0f) # 0xf is max for XOR encodings - non-unicode max = 0x0f Rex::Text.shuffle_a( [* ( (0..(max-1)).map { |i| i *= 0x10 } ) ] ) end def Generic.gen_second(block, base) # XOR encoder for ascii - unicode uses additive (block^base) end def Generic.encode_byte(block, badchars) accepted_chars = @@default_accepted_chars.dup # Remove bad chars from the accepted_chars list. Sadly 'A' must be # an accepted char or we'll certainly fail at this point. This could # be fixed later maybe with some recalculation of the encoder stubs... # - Puss (badchars || '').split('').each { |c| accepted_chars.delete(c) } first = 0 second = 1 randbase = 0 gen_base_set(block).each do |randbase| second = gen_second(block, randbase) next if second < 0 break if accepted_chars.include?(second.chr) end raise RuntimeError, "Negative" if second < 0 raise RuntimeError, "BadChar; #{block} to #{second}" if not accepted_chars.include?(second.chr) if (randbase > 0xa0) # first num must be 4 first = (randbase/0x10) + 0x40 elsif (randbase == 0x00) || (randbase == 0x10) # first num must be 5 first = (randbase/0x10) + 0x50 else # pick one at "random" first = (randbase/0x10) if (first % 2) first += 0x40 else randbase += 0x50 end end # now add our new bytes :) first.to_i.chr + second.chr end def Generic.encode(buf, reg, offset, badchars = '') encoded = gen_decoder(reg, offset) buf.each_byte { |block| encoded += encode_byte(block, badchars) } encoded += add_terminator() return encoded end # 'A' signifies the end of the encoded shellcode def Generic.add_terminator() 'AA' end end end end end