Class: Rex::Encoding::Xor::Generic

Inherits:
Object
  • Object
show all
Defined in:
lib/rex/encoding/xor/generic.rb

Direct Known Subclasses

Byte, Dword, DwordAdditive, Qword, Word

Class Method Summary collapse

Class Method Details

._check(data, key, badchars) ⇒ Object

hook stylies! return index of offending byte or nil


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# File 'lib/rex/encoding/xor/generic.rb', line 25

def Generic._check(data, key, badchars)
  return _check_key(key, badchars) || _check_encode(data, key, badchars)
end

._check_encode(data, key, badchars) ⇒ Object


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# File 'lib/rex/encoding/xor/generic.rb', line 31

def Generic._check_encode(data, key, badchars)
  return Rex::Text.badchar_index(encode(data, key), badchars)
end

._check_key(key, badchars) ⇒ Object


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# File 'lib/rex/encoding/xor/generic.rb', line 28

def Generic._check_key(key, badchars)
  return Rex::Text.badchar_index(key, badchars)
end

._encode_mutate_key(buf, key, pos, len) ⇒ Object

kind of ghetto, but very convenient for mutating keys by default, do no key mutations


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# File 'lib/rex/encoding/xor/generic.rb', line 134

def Generic._encode_mutate_key(buf, key, pos, len)
  return key
end

._find_bad_keys(data, badchars) ⇒ Object

Find a list of bytes that can't be valid xor keys, from the data and badchars. This returns a Array of hashes, length keysize


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# File 'lib/rex/encoding/xor/generic.rb', line 45

def Generic._find_bad_keys(data, badchars)

  ksize = keysize

  # array of hashes for the bad characters based
  # on their position in the data
  badkeys = [ ]
  ksize.times { badkeys << { } }

  badchars.each_byte { |badchar|
    pos = 0
    data.each_byte { |char|
      badkeys[pos % ksize][char ^ badchar] = true
      pos += 1
    }
  }

  return badkeys
end

._find_good_key(data, badkeys, badchars) ⇒ Object

(Hopefully) find a good key, from badkeys and badchars


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# File 'lib/rex/encoding/xor/generic.rb', line 68

def Generic._find_good_key(data, badkeys, badchars)

  ksize = keysize
  strip = 0
  key   = ""

  while strip < keysize

    kbyte = rand(256)

    catch(:found_kbyte) do
      256.times {

        if !badkeys[strip][kbyte] && !badchars[kbyte.chr]
          throw :found_kbyte
        end

        kbyte = (kbyte + 1) & 0xff
      }

      raise KeySearchError, "Exhausted byte space for strip #{strip}!", caller
    end

    key << kbyte
    strip += 1
  end

  # ok, we should have a good key now, lets double check...
  if _check(data, key, badchars)
    raise KeySearchError, "Key found, but bad character check failed!", caller
  end

  return key
end

.encode(buf, key) ⇒ Object


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# File 'lib/rex/encoding/xor/generic.rb', line 103

def Generic.encode(buf, key)

  if !key.kind_of?(String)
    raise ::ArgumentError, "Key must be a string!", caller
  end

  len = key.length

  if len == 0
    raise ::ArgumentError, "Zero key length!", caller
  end

  if keysize != 0 && keysize != len
    raise ::ArgumentError, "Key length #{len}, expected #{keysize}", caller
  end

  encoded = ""
  pos     = 0

  while pos < buf.length
    encoded += (buf[pos,1].unpack("C*")[0] ^ key[pos % len, 1].unpack("C*")[0]).chr
    key = _encode_mutate_key(buf, key, pos, len)
    pos += 1
  end

  return [ encoded, key ]

end

.find_key(data, badchars) ⇒ Object


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# File 'lib/rex/encoding/xor/generic.rb', line 35

def Generic.find_key(data, badchars)
  return _find_good_key(data, _find_bad_keys(data, badchars), badchars)
end

.find_key_and_encode(data, badchars) ⇒ Object

maybe a bit a smaller of method name?


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# File 'lib/rex/encoding/xor/generic.rb', line 139

def Generic.find_key_and_encode(data, badchars)
  key        = find_key(data, badchars)
  enc, fkey  = encode(data, key)
  return [ enc, key, fkey ]
end

.keysizeObject


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# File 'lib/rex/encoding/xor/generic.rb', line 12

def Generic.keysize
  # special case:
  # 0 means we encode based on the length of the key
  # we don't enforce any perticular key length
  return 0
end