Class: BiCrypt

Inherits:
Object
  • Object
show all
Defined in:
lib/bicrypt.rb

Overview

BiCrypt

A simple two-way encryption class.

This class is based on algorithms given in Applied Cryptography 2nd Ed.

If subclassed, the new encryption class must provide three methods:

  • encrypt_block(block)

  • decrypt_block(block)

  • block_size()

Constant Summary collapse

VERSION = 
'1.2.0'
ULONG = 
0x100000000
SBOX =

These are the S-boxes given in Applied Cryptography 2nd Ed., p. 333

[
  [4, 10, 9, 2, 13, 8, 0, 14, 6, 11, 1, 12, 7, 15, 5, 3],
  [14, 11, 4, 12, 6, 13, 15, 10, 2, 3, 8, 1, 0, 7, 5, 9],
  [5, 8, 1, 13, 10, 3, 4, 2, 14, 15, 12, 7, 6, 0, 9, 11],
  [7, 13, 10, 1, 0, 8, 9, 15, 14, 4, 6, 12, 11, 2, 5, 3],
  [6, 12, 7, 1, 5, 15, 13, 8, 4, 10, 9, 14, 0, 3, 11, 2],
  [4, 11, 10, 0, 7, 2, 1, 13, 3, 6, 8, 5, 9, 12, 15, 14],
  [13, 11, 4, 1, 3, 15, 5, 9, 0, 10, 14, 7, 6, 8, 2, 12],
  [1, 15, 13, 0, 5, 7, 10, 4, 9, 2, 3, 14, 6, 11, 8, 12]
]

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(userKey) ⇒ BiCrypt

Returns a new instance of BiCrypt.



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# File 'lib/bicrypt.rb', line 61

def initialize(userKey)
  @sBox = SBOX

  if userKey.size < 8
    userKey += '01234567'
  end

  #@sTable = precalculate_s_table()

  # derive the 32-byte key from the user-supplied key
  userKeyLength = userKey.length

  @key = userKey[0..31].unpack('C'*32)

  if (userKeyLength < 32)
    userKeyLength.upto(31) { @key << 0 }
  end
end

Instance Attribute Details

#sBox ⇒ Object (readonly, private)

S-boxes.



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# File 'lib/bicrypt.rb', line 170

def sBox
  @sBox
end

Instance Method Details

#block_size ⇒ Object (private) 



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# File 'lib/bicrypt.rb', line 205

def block_size
  8
end

#carefully_open_file(filename, mode) ⇒ Object (private) 



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# File 'lib/bicrypt.rb', line 273

def carefully_open_file(filename, mode)
  begin
    aFile = File.new(filename, mode)
  rescue
    puts "Sorry. There was a problem opening the file <#{filename}>."
    aFile.close() unless aFile.nil?
    raise
  end
  return(aFile)
end

#decrypt_block(block) ⇒ Object (private) 



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# File 'lib/bicrypt.rb', line 197

def decrypt_block(block)
  xl, xr = block.unpack('NN')
  xl, xr = decrypt_pair(xl, xr)
  decrypted = [xl, xr].pack('NN')
  return(decrypted)
end

#decrypt_file(cryptFilename, plainFilename) ⇒ Object

Decrypt an encrypted file.



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# File 'lib/bicrypt.rb', line 141

def decrypt_file(cryptFilename, plainFilename)
  cryptFile = carefully_open_file(cryptFilename, 'rb')
  plainFile = carefully_open_file(plainFilename, 'wb+')
  decrypt_stream(cryptFile, plainFile)
  cryptFile.close unless cryptFile.closed?
  plainFile.close unless plainFile.closed?
end

#decrypt_pair(xl, xr) ⇒ Object (private) 



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# File 'lib/bicrypt.rb', line 233

def decrypt_pair(xl, xr)
  xr ^= f(xl+@key[0])
  xl ^= f(xr+@key[1])
  xr ^= f(xl+@key[2])
  xl ^= f(xr+@key[3])
  xr ^= f(xl+@key[4])
  xl ^= f(xr+@key[5])
  xr ^= f(xl+@key[6])
  xl ^= f(xr+@key[7])
  3.times {
    xr ^= f(xl+@key[7])
    xl ^= f(xr+@key[6])
    xr ^= f(xl+@key[5])
    xl ^= f(xr+@key[4])
    xr ^= f(xl+@key[3])
    xl ^= f(xr+@key[2])
    xr ^= f(xl+@key[1])
    xl ^= f(xr+@key[0])
  }
  return([xr, xl])
end

#decrypt_stream(cryptStream, plainStream) ⇒ Object

Decrypt an encrypted IO stream.



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# File 'lib/bicrypt.rb', line 114

def decrypt_stream(cryptStream, plainStream)
  # Cypher-block-chain mode
  chain = cryptStream.read(block_size())

  while (block = cryptStream.read(block_size()))
    decrypted = decrypt_block(block)
    plainText = xor(decrypted, chain)
    plainStream.write(plainText) unless cryptStream.eof?
    chain = block
  end

  # write the final block, omitting the padding
  buffer = plainText.split('')
  remainingMessageBytes = buffer.last.unpack('C').first
  remainingMessageBytes.times { plainStream.write(buffer.shift) }
end

#decrypt_string(cryptText) ⇒ Object

Decrypt an encrypted string.



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# File 'lib/bicrypt.rb', line 159

def decrypt_string(cryptText)
  cryptStream = StringIO.new(cryptText)
  plainStream = StringIO.new('')
  decrypt_stream(cryptStream, plainStream)
  plainText = plainStream.string
  return(plainText)
end

#encrypt_block(block) ⇒ Object (private) 



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# File 'lib/bicrypt.rb', line 189

def encrypt_block(block)
  xl, xr = block.unpack('NN')
  xl, xr = encrypt_pair(xl, xr)
  encrypted = [xl, xr].pack('NN')
  return(encrypted)
end

#encrypt_file(plainFilename, cryptFilename) ⇒ Object

Encrypt a file.



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# File 'lib/bicrypt.rb', line 132

def encrypt_file(plainFilename, cryptFilename)
  plainFile = carefully_open_file(plainFilename, 'rb')
  cryptFile = carefully_open_file(cryptFilename, 'wb+')
  encrypt_stream(plainFile, cryptFile)
  plainFile.close unless plainFile.closed?
  cryptFile.close unless cryptFile.closed?
end

#encrypt_pair(xl, xr) ⇒ Object (private) 



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# File 'lib/bicrypt.rb', line 210

def encrypt_pair(xl, xr)
  3.times {
    xr ^= f(xl+@key[0])
    xl ^= f(xr+@key[1])
    xr ^= f(xl+@key[2])
    xl ^= f(xr+@key[3])
    xr ^= f(xl+@key[4])
    xl ^= f(xr+@key[5])
    xr ^= f(xl+@key[6])
    xl ^= f(xr+@key[7])
  }
  xr ^= f(xl+@key[7])
  xl ^= f(xr+@key[6])
  xr ^= f(xl+@key[5])
  xl ^= f(xr+@key[4])
  xr ^= f(xl+@key[3])
  xl ^= f(xr+@key[2])
  xr ^= f(xl+@key[1])
  xl ^= f(xr+@key[0])
  return([xr, xl])
end

#encrypt_stream(plainStream, cryptStream) ⇒ Object

Encrypt an IO stream.



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# File 'lib/bicrypt.rb', line 83

def encrypt_stream(plainStream, cryptStream)
  # Cypher-block-chain mode

  initVector = generate_initialization_vector(block_size() / 4)
  chain = encrypt_block(initVector)
  cryptStream.write(chain)

  while ((block = plainStream.read(block_size())) && (block.length == block_size()))
    block = xor(block, chain)
    encrypted = encrypt_block(block)
    cryptStream.write(encrypted)
    chain = encrypted
  end

  # write the final block
  # At most block_size()-1 bytes can be part of the message.
  # That means the final byte can be used to store the number of meaningful
  # bytes in the final block
  block = '' if block.nil?
  buffer = block.split('')
  remainingMessageBytes = buffer.length
  # we use 7-bit characters to avoid possible strange behavior on the Mac
  remainingMessageBytes.upto(block_size()-2) { buffer << rand(128).chr }
  buffer << remainingMessageBytes.chr
  block = buffer.join('')
  block = xor(block, chain)
  encrypted = encrypt_block(block)
  cryptStream.write(encrypted)
end

#encrypt_string(plainText) ⇒ Object

Encrypt a string.



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# File 'lib/bicrypt.rb', line 150

def encrypt_string(plainText)
  plainStream = StringIO.new(plainText)
  cryptStream = StringIO.new('')
  encrypt_stream(plainStream, cryptStream)
  cryptText = cryptStream.string
  return(cryptText)
end

#f(longWord) ⇒ Object (private) 



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# File 'lib/bicrypt.rb', line 256

def f(longWord)
  longWord = longWord % ULONG
  a, b, c, d = [longWord].pack('L').unpack('CCCC')
  return(sTable[3][d] ^ sTable[2][c] ^ sTable[1][b] ^ sTable[0][a])
end

#generate_initialization_vector(words) ⇒ Object (private) 



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# File 'lib/bicrypt.rb', line 263

def generate_initialization_vector(words)
  srand(Time.now.to_i)
  vector = ""
  words.times {
    vector << [rand(ULONG)].pack('N')
  }
  return(vector)
end

#sTable ⇒ Object (private)

Calculated S-boxes



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# File 'lib/bicrypt.rb', line 173

def sTable
  @sTable ||= (
    sTable = [[], [], [], []]
    0.upto(3) { |i|
      0.upto(255) { |j|
        t = sBox[2*i][j % 16] | (sBox[2*i+1][j/16] << 4)
        u = (8*i + 11) % 32
        v = (t << u) | (t >> (32-u))
        sTable[i][j] = (v % ULONG)
      }
    }
    sTable
  )
end

#xor(str1, str2) ⇒ Object (private)

Binary XOR of two strings. 

puts "\000\000\001\001" ^ "\000\001\000\001"
puts  "\003\003\003" ^ "\000\001\002"

produces

"\000\001\001\000"
"\003\002\001"

– NOTE: This used to be a String#^ extension in v1.0. So if an uncaught bug should arise check this first. ++



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# File 'lib/bicrypt.rb', line 298

def xor(str1, str2)
  a = str1.unpack('C'*(str1.length)) #.bytes.to_a
  b = str2.unpack('C'*(str2.length)) #.bytes.to_a
  if (b.length < a.length)
    (a.length - b.length).times { b << 0 }
  end
  xor = ""
  0.upto(a.length - 1) do |pos|
    x = a[pos] ^ b[pos]
    xor << x.chr()
  end
  return(xor)
end