Module: ZSteg::Checker::WBStego

Defined in:
lib/zsteg/checker/wbstego.rb

Defined Under Namespace

Classes: Result

Constant Summary collapse

ENCRYPTIONS = 
[
  nil,         # 0
  "Blowfish",  # 1
  "Twofish",   # 2
  "CAST128",   # 3
  "Rijndael",  # 4
]

Class Method Summary collapse

Class Method Details

.calc_avail_size(image) ⇒ Object

from wbStego4open sources



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# File 'lib/zsteg/checker/wbstego.rb', line 69

def calc_avail_size image
 space = 0
 biHeader = image.hdr
 if biHeader.biCompression == 0
   case biHeader.biBitCount
   when 4
     space = 2*image.imagedata_size if used_colors < 9
   when 8
     space = image.imagedata_size if used_colors < 129
   when 24
     space = image.imagedata_size
   end
 else
   raise "TODO"
#           if biHeader.biBitCount=4 then begin
#             if UsedColors<9 then space:=GetAvailSizeRLE else space:=0;
#           end;
#           if biHeader.biBitCount=8 then begin
#             if UsedColors<129 then space:=GetAvailSizeRLE else space:=0;
#           end;
 end
 space/8
end

.check(data, params = {}) ⇒ Object 



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# File 'lib/zsteg/checker/wbstego.rb', line 93

def check data, params = {}
  return if data.size < 4
  return if params[:bit_order] != :lsb

  force_color = nil

  if params[:image].format == :bmp
    return if params[:order] !~ /b/i
  else
    # PNG
    return if Array(params[:channels]).join != 'bgr'
    force_color = :gray if params[:order] != 'xY'
  end

  size1 = (data[0,3] + "\x00").unpack('V')[0]
  avail_size =
    if params[:image].format == :bmp
      calc_avail_size(params[:image])
    else
      params[:max_hidden_size]
    end
  return if size1 == 0 || size1 > avail_size

  # check if too many zeroes, prevent false positive
  nzeroes = data[3..-1].count("\x00")
  return if nzeroes > 10 && data.size-3-nzeroes < 4

  result = nil

  size2 = (data[3,3] + "\x00").unpack('V')[0]
#          p [size1, size2, avail_size]
  if size2 < avail_size && size2 > 0
    spacing = 1.0*avail_size/(size2+5) - 1
#            puts "[d] spacing=#{spacing}"
    if spacing > 0
      error = 0
      r = ''
      6.upto(data.size-1) do |idx|
        if error < 1
          r << data[idx]
          error += spacing
        else
          error -= 1
        end
      end
      if r.size > 4
        ext = r[0,3]
        result = Result.new(size2, ext, r[3..-1], true)
      end
    end
  end
  # no even distribution
  #return unless valid_ext?(data[3,3])
  result ||= Result.read(data)
  result.color = force_color if result && force_color
  result

rescue
  STDERR.puts "[!] wbStego: #{$!.inspect}".red
end

.used_colors ⇒ Object 



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# File 'lib/zsteg/checker/wbstego.rb', line 64

def used_colors
  raise "TODO"
end