Class: Rex::Encoder::Alpha2::AlphaMixed

Inherits:
Generic
  • Object
show all
Defined in:
lib/rex/encoder/alpha2/alpha_mixed.rb

Class Method Summary collapse

Methods inherited from Generic

add_terminator, default_accepted_chars, encode, encode_byte, gen_second

Class Method Details

.gen_decoder(reg, offset) ⇒ Object 



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# File 'lib/rex/encoder/alpha2/alpha_mixed.rb', line 45

def self.gen_decoder(reg, offset)
  decoder =
     gen_decoder_prefix(reg, offset) +
     "jA" +          # push 0x41
     "X" +           # pop eax
     "P" +           # push eax
     "0A0" +         # xor byte [ecx+30], al
     "A" +           # inc ecx                        <---
     "kAAQ" +        # imul eax, [ecx+42], 51 -> 10       |
     "2AB" +         # xor al, [ecx + 42]                 |
     "2BB" +         # xor al, [edx + 42]                 |
     "0BB" +         # xor [edx + 42], al                 |
     "A" +           # inc ecx                            |
     "B" +           # inc edx                            |
     "X" +           # pop eax                            |
     "P" +           # push eax                           |
     "8AB" +         # cmp [ecx + 42], al                 |
     "uJ" +          # jnz short -------------------------
     "I"             # first encoded char, fixes the above J

  return decoder
end

.gen_decoder_prefix(reg, offset) ⇒ Object 



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# File 'lib/rex/encoder/alpha2/alpha_mixed.rb', line 11

def self.gen_decoder_prefix(reg, offset)
  if (offset > 32)
    raise "Critical: Offset is greater than 32"
  end

  # use inc ebx as a nop here so we still pad correctly
  if (offset <= 16)
    nop = 'C' * offset
    mod = 'I' * (16 - offset) + nop + '7QZ'    # dec ecx,,, push ecx, pop edx
    edxmod = 'J' * (17 - offset)
  else
    mod = 'A' * (offset - 16)
    nop = 'C' * (16 - mod.length)
    mod << nop + '7QZ'
    edxmod = 'B' * (17 - (offset - 16))
  end
  regprefix = {
    'EAX'   => 'PY' + mod,                         # push eax, pop ecx
    'ECX'   => 'I' + mod,                          # dec ecx
    'EDX'   =>  edxmod + nop + '7RY',			   # dec edx,,, push edx, pop ecx
    'EBX'   => 'SY' + mod,                         # push ebx, pop ecx
    'ESP'   => 'TY' + mod,                         # push esp, pop ecx
    'EBP'   => 'UY' + mod,                         # push ebp, pop ecx
    'ESI'   => 'VY' + mod,                         # push esi, pop ecx
    'EDI'   => 'WY' + mod,                         # push edi, pop ecx
  }

  reg.upcase!
  if (not regprefix.keys.include? reg)
    raise ArgumentError.new("Invalid register name")
  end
  return regprefix[reg]
end