Class: Rex::Encoder::Alpha2::AlphaUpper

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

Class Method Summary collapse

Methods inherited from Generic

add_terminator, encode, encode_byte, gen_second

Class Method Details

.default_accepted_chars ⇒ Object 



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# File 'lib/rex/encoder/alpha2/alpha_upper.rb', line 10

def self.default_accepted_chars ; ('B' .. 'Z').to_a + ('0' .. '9').to_a ; end

.gen_decoder(reg, offset) ⇒ Object 



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# File 'lib/rex/encoder/alpha2/alpha_upper.rb', line 47

def self.gen_decoder(reg, offset)
  decoder =
    gen_decoder_prefix(reg, offset) +
    "V" +           # push esi
    "T" +           # push esp
    "X" +           # pop eax
    "30" +          # xor esi, [eax]
    "V" +           # push esi
    "X" +           # pop eax
    "4A" +          # xor al, 41
    "P" +           # push eax
    "0A3" +         # xor [ecx+33], al
    "H" +           # dec eax
    "H" +           # dec eax
    "0A0" +         # xor [ecx+30], al
    "0AB" +         # xor [ecx+42], al
    "A" +           # inc ecx   <---------------
    "A" +           # inc ecx                   |
    "B" +           # inc edx                   |
    "TAAQ" +        # imul eax, [ecx+41], 10 *  |
    "2AB" +         # xor al [ecx+42]           |
    "2BB" +         # xor al, [edx+42]          |
    "0BB" +         # xor [edx+42], al          |
    "X" +           # pop eax                   |
    "P" +           # push eax                  |
    "8AC" +         # cmp [ecx+43], al          |
    "JJ" +          # jnz * --------------------
    "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_upper.rb', line 12

def self.gen_decoder_prefix(reg, offset)
  if (offset > 20)
    raise "Critical: Offset is greater than 20"
  end

  # use inc ebx as a nop here so we still pad correctly
  if (offset <= 10)
    nop = 'C' * offset
    mod = 'I' * (10 - offset) + nop + 'QZ'    # dec ecx,,, push ecx, pop edx
    edxmod = 'J' * (11 - offset)
  else
    mod = 'A' * (offset - 10)
    nop = 'C' * (10 - mod.length)
    mod << nop + 'QZ'
    edxmod = 'B' * (11 - (offset - 10))
  end
  regprefix = {
    'EAX'   => 'PY' + mod,                        # push eax, pop ecx
    'ECX'   => 'I' + mod,                         # dec ecx
    'EDX'   =>  edxmod + nop + 'RY',  			  # mod 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 edi
  }

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

end