class Unveiler

Unveiler is a basic steganography tool that encodes data by manipulating existing binary data and can decode previously encoded data.

Author: Brendan Goodenough
Copyright: Copyright © 2016 Brendan Goodenough
License: MIT

The encoding of the data is achieved by manipulating the least significant bits of each byte in the target data. These bits are replaced with the next sequential bit of the data to be encoded, looping until the end of the data is reached.

Decoding is achieved by looping through each byte of the target data, and stringing together the least significant bits of each byte. This is repeated until the last 3 bytes in the string of bits forms the phrase 'EOF'.

Public Class Methods

decode(target) click to toggle source

Decodes any data within the specified target data. Upon success, the decoded string will be returned.

target: Target data to be decoded

# File lib/unveiler.rb, line 49
def self.decode(target)
  raise ArgumentError, 'target must be a String' unless target.is_a? String

  # Convert the target data into an array of bytes
  bytes = target.unpack('B*')[0].scan(/.{8}/)

  # Obtain string from the bytes
  bytes = self.process_bytes(bytes)
  return Base64.decode64(bytes)
end

encode(target, data) click to toggle source

Encodes the specified string of data into the target data. Upon success, a UTF-8 string containing the manipulated data will be returned.

target: Target data to be manipulated
data: Data to encode

# File lib/unveiler.rb, line 25
def self.encode(target, data)
  raise ArgumentError, 'target must be a string' unless target.is_a? String
  raise ArgumentError, 'data must be a string' unless data.is_a? String

  # Convert target data into an array of bytes
  bytes = target.unpack('B*')[0].scan(/.{8}/)

  # Convert data to binary
  data = Base64.encode64(data)
  data += 'EOF'
  data = data.unpack('B*').first

  # Encode the data into the array of bytes
  bytes = self.manipulate_bytes(bytes, data)

  # Convert binary to UTF-8
  bytes.map!{|byte| byte = byte.to_i(2)}
  return bytes.pack('C*').force_encoding('utf-8')
end

manipulate_bytes(bytes, data) click to toggle source

Manipulates an array of bytes by looping through and replacing the least significant bit of each byte with the next sequential bit in a string of binary data. The loop will break when the end of the data string is reached. Returns the manipulated array of bytes.

bytes: Array of bytes to manipulate
data: Binary data to insert

# File lib/unveiler.rb, line 67
def self.manipulate_bytes(bytes, data)
  count = 0

  8.times do |index|
    # Loop through each byte and replace the bit at the given index
    bytes.reverse.each do |byte|
      byte[7 - index] = data[count]
      count += 1
      return bytes if count == data.length
    end
  end

  # Ran out of space to encode data
  raise 'Input file is too small for the specified data'
end

process_bytes(bytes) click to toggle source

Processes the specified array of bytes by looping through each byte and appending the least significant bit onto a string of bits. At the end of every eighth bit, a check will be made to see if the last 3 bytes of the string contain the phrase 'EOF'. Only the bytes before EOF will be returned if the phrase is found. An error will be raised if no EOF is found.

bytes: Array of bytes to be processed

# File lib/unveiler.rb, line 90
def self.process_bytes(bytes)
  eof = '010001010100111101000110' # binary "EOF"
  bits = ''

  8.times do |index|
    bytes.reverse.each do |byte|
      # Least significant bit
      bits += byte[7 - index]

      # Check whether a full byte has been read
      if bits.length % 8 == 0 && bits.length >= 24
        if bits[-24..-1] == eof
          # Convert bits to array of bytes
          data = bits.scan(/.{8}/)

          # Convert bytes to a UTF-8 string
          data.map!{|b| byte = b.to_i(2)}
          data = data.pack('C*').force_encoding('utf-8')

          return data[0..data.length - 3]
        end
      end
    end
  end

  # No EOF was found, error
  raise 'No phrase matching "EOF" was found'
end