Class: Crypt::Rijndael

Inherits:
Object show all
Includes:
CBC, RijndaelTables
Defined in:
lib/flatulent/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(userKey, keyBits = 256, blockBits = 128) ⇒ Rijndael

Returns a new instance of Rijndael.



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# File 'lib/flatulent/crypt/rijndael.rb', line 19

def initialize(userKey, keyBits = 256, blockBits = 128)
  case keyBits
    when 128 
      @keyWords = 4
    when 192 
      @keyWords = 6
    when 256
      @keyWords = 8
    else raise "The key must be 128, 192, or 256 bits long."
  end
  
  case (keyBits >= blockBits) ? keyBits : blockBits
    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 blockBits
    when 128 
      @blockSize = 16
      @blockWords = 4
      @shiftIndex = 0
    when 192 
      @blockSize = 24
      @blockWords = 6
      @shiftIndex = 1
    when 256 
      @blockSize = 32
      @blockWords = 8
      @shiftIndex = 2
    else raise "The block size must be 128, 192, or 256 bits long."
  end
  
  uk = userKey.unpack('C'*userKey.length)
  maxUsefulSizeOfUserKey = (keyBits/8)
  uk = uk[0..maxUsefulSizeOfUserKey-1]    # truncate
  padding = 0
  if (userKey.length < keyBits/8)
    shortfallInUserKey = (keyBits/8 - userKey.length)
    shortfallInUserKey.times { uk << padding }
  end
  @key = [[], [], [], []]
  0.upto(uk.length-1) { |pos|
    @key[pos % 4][pos / 4] = uk[pos]
  }
  @roundKeys = generate_key_schedule(@key, keyBits, blockBits)
end

Instance Method Details

#add_round_key(blockArray, roundKey) ⇒ Object 



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# File 'lib/flatulent/crypt/rijndael.rb', line 87

def add_round_key(blockArray, roundKey)
0.upto(3) { |i|
  0.upto(@blockWords) { |j|
    blockArray[i][j] ^= roundKey[i][j]
  }
}
return(blockArray)
end

#block_size ⇒ Object 



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# File 'lib/flatulent/crypt/rijndael.rb', line 72

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

#decrypt_block(block) ⇒ Object 



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# File 'lib/flatulent/crypt/rijndael.rb', line 253

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

#decrypt_byte_array(blockArray) ⇒ Object 



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# File 'lib/flatulent/crypt/rijndael.rb', line 236

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

#encrypt_block(block) ⇒ Object 



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# File 'lib/flatulent/crypt/rijndael.rb', line 221

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

#encrypt_byte_array(blockArray) ⇒ Object 



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# File 'lib/flatulent/crypt/rijndael.rb', line 205

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

#generate_key_schedule(k, keyBits, blockBits) ⇒ Object 



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# File 'lib/flatulent/crypt/rijndael.rb', line 150

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

#inverse_mix_columns(blockArray) ⇒ Object 



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# File 'lib/flatulent/crypt/rijndael.rb', line 136

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

#mix_columns(blockArray) ⇒ Object 



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# File 'lib/flatulent/crypt/rijndael.rb', line 122

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

#mul(a, b) ⇒ Object 



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# File 'lib/flatulent/crypt/rijndael.rb', line 77

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(blockArray, direction) ⇒ Object 



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# File 'lib/flatulent/crypt/rijndael.rb', line 97

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

#substitution(blockArray, sBox) ⇒ Object 



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# File 'lib/flatulent/crypt/rijndael.rb', line 111

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