Class: Crypt::Rijndael

Inherits:
Object
  • Object
show all
Includes:
CBC, RijndaelTables
Defined in:
lib/crypt/rijndael.rb

Constant Summary

Constants included from RijndaelTables

Crypt::RijndaelTables::AlogTable, Crypt::RijndaelTables::IG, Crypt::RijndaelTables::LogTable, Crypt::RijndaelTables::Rcon, Crypt::RijndaelTables::S, Crypt::RijndaelTables::Shifts, Crypt::RijndaelTables::Si

Constants included from CBC

CBC::ULONG

Instance Method Summary collapse

Methods included from CBC

#carefully_open_file, #decrypt_file, #decrypt_stream, #decrypt_string, #encrypt_file, #encrypt_stream, #encrypt_string, #generate_initialization_vector

Constructor Details

#initialize(user_key, key_bits = 256, block_bits = 128) ⇒ Rijndael

Returns a new instance of Rijndael.



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# File 'lib/crypt/rijndael.rb', line 16

def initialize(user_key, key_bits = 256, block_bits = 128)
  case key_bits
    when 128 
      @key_words = 4
    when 192 
      @key_words = 6
    when 256
      @key_words = 8
    else raise "The key must be 128, 192, or 256 bits long."
  end

  case (key_bits >= block_bits) ? key_bits : block_bits
    when 128 
      @rounds = 10
    when 192 
      @rounds = 12
    when 256
      @rounds = 14
    else raise "The key and block sizes must be 128, 192, or 256 bits long."
  end
   
  case block_bits
    when 128 
      @block_size = 16
      @block_words = 4
      @shift_index = 0
    when 192 
      @block_size = 24
      @block_words = 6
      @shift_index = 1
    when 256 
      @block_size = 32
      @block_words = 8
      @shift_index = 2
    else raise "The block size must be 128, 192, or 256 bits long."
  end

  uk = user_key.unpack('C'*user_key.length)
  max_useful_size_of_user_key = (key_bits/8)
  uk = uk[0..max_useful_size_of_user_key-1]    # truncate
  padding = 0
  if (user_key.length < key_bits/8)
    shortfall_in_user_key = (key_bits/8 - user_key.length)
    shortfall_in_user_key.times { uk << padding }
  end
  @key = [[], [], [], []]
  0.upto(uk.length-1) { |pos|
    @key[pos % 4][pos / 4] = uk[pos]
  }
  @round_keys = generate_key_schedule(@key, key_bits, block_bits)
end

Instance Method Details

#add_round_key(block_array, round_key) ⇒ Object 



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# File 'lib/crypt/rijndael.rb', line 84

def add_round_key(block_array, round_key)
0.upto(3) { |i|
  0.upto(@block_words) { |j|
    block_array[i][j] ^= round_key[i][j]
  }
}
return(block_array)
end

#block_size ⇒ Object 



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# File 'lib/crypt/rijndael.rb', line 69

def block_size
  return(@block_size) # needed for CBC
end

#decrypt_block(block) ⇒ Object 



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# File 'lib/crypt/rijndael.rb', line 251

def decrypt_block(block)
  raise "block must be #{@block_size} bytes long" if (block.length() != @block_size)
  block_array = [[], [], [], []]
  block_bytes = block.bytes.to_a
  0.upto(@block_size - 1) { |pos|
    block_array[pos % 4][pos / 4] = block_bytes[pos]
  }
  decrypted_block = decrypt_byte_array(block_array)
  decrypted = ""
  0.upto(@block_size - 1) { |pos|
    decrypted << decrypted_block[pos % 4][pos / 4]
  }
  return(decrypted)
end

#decrypt_byte_array(block_array) ⇒ Object 



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# File 'lib/crypt/rijndael.rb', line 234

def decrypt_byte_array(block_array)
  # first special round without inverse_mix_columns
  # add_round_key is an involution - applying it a second time returns the original result
  block_array = add_round_key(block_array, @round_keys[@rounds]) 
  block_array = substitution(block_array,Si)   # using inverse S-box
  block_array = shift_rows(block_array,1)
  (@rounds-1).downto(1) { |round|
    block_array = add_round_key(block_array, @round_keys[round])
    block_array = inverse_mix_columns(block_array)
    block_array = substitution(block_array, Si) 
    block_array = shift_rows(block_array, 1)
  }
  block_array = add_round_key(block_array, @round_keys[0])
  return(block_array)
end

#encrypt_block(block) ⇒ Object 



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# File 'lib/crypt/rijndael.rb', line 218

def encrypt_block(block)
  raise "block must be #{@block_size} bytes long" if (block.length() != @block_size)
  block_array = [[], [], [], []]
  block_bytes = block.bytes.to_a
  0.upto(@block_size - 1) { |pos|
    block_array[pos % 4][pos / 4] = block_bytes[pos]
  }
  encrypted_block = encrypt_byte_array(block_array)
  encrypted = ""
  0.upto(@block_size - 1) { |pos|
    encrypted << encrypted_block[pos % 4][pos / 4]
  }
  return(encrypted)
end

#encrypt_byte_array(block_array) ⇒ Object 



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# File 'lib/crypt/rijndael.rb', line 202

def encrypt_byte_array(block_array)
  block_array = add_round_key(block_array, @round_keys[0])
  1.upto(@rounds - 1) { |round|
    block_array = substitution(block_array, S)
    block_array = shift_rows(block_array, 0)
    block_array = mix_columns(block_array)
    block_array = add_round_key(block_array, @round_keys[round])
  }
  # special round without mix_columns
  block_array = substitution(block_array,S)
  block_array = shift_rows(block_array,0)
  block_array = add_round_key(block_array, @round_keys[@rounds])
  return(block_array)
end

#generate_key_schedule(k, key_bits, block_bits) ⇒ Object 



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# File 'lib/crypt/rijndael.rb', line 147

def generate_key_schedule(k, key_bits, block_bits)
  tk = k[0..3][0..@key_words-1]  # using slice to get a copy instead of a reference
  key_sched = []
  (@rounds + 1).times { key_sched << [[], [], [], []] }
  t = 0
  j = 0
  while ((j < @key_words) && (t < (@rounds+1)*@block_words))
    0.upto(3) { |i|
      key_sched[t / @block_words][i][t % @block_words] = tk[i][j]
    }
    j += 1
    t += 1
  end
  # while not enough round key material collected, calculate new values
  rcon_index = 0
  while (t < (@rounds+1)*@block_words) 
    0.upto(3) { |i|
      tk[i][0] ^= S[tk[(i + 1) % 4][@key_words - 1]]
    }
    tk[0][0] ^= Rcon[rcon_index]
    rcon_index = rcon_index.next
    if (@key_words != 8)
      1.upto(@key_words - 1) { |j|
        0.upto(3) { |i|
          tk[i][j] ^= tk[i][j-1];
        }
      }
    else
      1.upto(@key_words/2 - 1) { |j|
        0.upto(3) { |i|
          tk[i][j] ^= tk[i][j-1]
        }
      }
      0.upto(3) { |i|
        tk[i][@key_words/2] ^= S[tk[i][@key_words/2 - 1]]
      }
      (@key_words/2 + 1).upto(@key_words - 1) { |j|
        0.upto(3) { |i| 
          tk[i][j] ^= tk[i][j-1] 
        }
      }
    end
    j = 0
    while ((j < @key_words) && (t < (@rounds+1) * @block_words))
      0.upto(3) { |i|
        key_sched[t / @block_words][i][t % @block_words] = tk[i][j]
      }
      j += 1
      t += 1
    end
  end
  return(key_sched)
end

#inverse_mix_columns(block_array) ⇒ Object 



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# File 'lib/crypt/rijndael.rb', line 133

def inverse_mix_columns(block_array)
  unmixed = [[], [], [], []]
  0.upto(@block_words-1) { |j|
    0.upto(3) { |i|
      unmixed[i][j] = mul(0xe, block_array[i][j]) ^
        mul(0xb, block_array[(i + 1) % 4][j]) ^                
        mul(0xd, block_array[(i + 2) % 4][j]) ^
        mul(0x9, block_array[(i + 3) % 4][j])
    }
  }
   return(unmixed)
end

#mix_columns(block_array) ⇒ Object 



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# File 'lib/crypt/rijndael.rb', line 119

def mix_columns(block_array)
  mixed = [[], [], [], []]
  0.upto(@block_words-1) { |j|
    0.upto(3) { |i|
      mixed[i][j] = mul(2,block_array[i][j]) ^
        mul(3,block_array[(i + 1) % 4][j]) ^
        block_array[(i + 2) % 4][j] ^
        block_array[(i + 3) % 4][j]
    }
  }
  return(mixed)
end

#mul(a, b) ⇒ Object 



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# File 'lib/crypt/rijndael.rb', line 74

def mul(a, b)
  if ((a ==0) | (b == 0))
    result = 0 
  else
    result = AlogTable[(LogTable[a] + LogTable[b]) % 255]
  end
  return(result)
end

#shift_rows(block_array, direction) ⇒ Object 



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# File 'lib/crypt/rijndael.rb', line 94

def shift_rows(block_array, direction)
  tmp = []
  1.upto(3) { |i|  # row zero remains unchanged
    0.upto(@block_words-1) { |j|
      tmp[j] = block_array[i][(j + Shifts[@shift_index][i][direction]) % @block_words]
    }
    0.upto(@block_words-1) { |j|
      block_array[i][j] = tmp[j]
    }
  }
  return(block_array)
end

#substitution(block_array, sBox) ⇒ Object 



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# File 'lib/crypt/rijndael.rb', line 108

def substitution(block_array, sBox)
  # replace every byte of the input with the byte at that position in the S-box
  0.upto(3) { |i|
    0.upto(@block_words-1) { |j|
      block_array[i][j] = sBox[block_array[i][j]]
    }
  }
  return(block_array)
end