lib/crypto/xor_ciphers.nit

   1 # This file is part of NIT ( http://www.nitlanguage.org ).
   2 #
   3 # Licensed under the Apache License, Version 2.0 (the "License");
   4 # you may not use this file except in compliance with the License.
   5 # You may obtain a copy of the License at
   6 #
   7 #     http://www.apache.org/licenses/LICENSE-2.0
   8 #
   9 # Unless required by applicable law or agreed to in writing, software
  10 # distributed under the License is distributed on an "AS IS" BASIS,
  11 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  12 # See the License for the specific language governing permissions and
  13 # limitations under the License.
  14
  15 # XOR oriented cryptographic ciphers and utilities.
  16 module xor_ciphers
  17
  18 redef class Bytes
  19         # Returns `self` xored with `key`
  20         #
  21         # The key is cycled through until the `self` has been completely xored.
  22         #
  23         #     assert "goodmorning".to_bytes.xorcipher(" ".to_bytes) == "GOODMORNING".bytes
  24         fun xorcipher(key: Bytes): Bytes do
  25                 var xored = new Bytes.with_capacity(self.length)
  26
  27                 for i in self.length.times do
  28                         xored.add(self[i] ^ key[i % key.length])
  29                 end
  30
  31                 return xored
  32         end
  33 end
  34
  35 # Base class to modelize cryptographic ciphers
  36 abstract class Cipher
  37
  38         # Encrypted data
  39         var ciphertext = new Bytes.empty is writable
  40
  41         # Unencrypted data
  42         var plaintext = new Bytes.empty is writable
  43
  44         # Encrypt plaintext and populate `self.ciphertext`
  45         fun encrypt is abstract
  46
  47         # Decrypt ciphertext and populate `self.plaintext`
  48         fun decrypt is abstract
  49
  50 end
  51
  52 # Simple XOR cipher where the whole plaintext is XORed with a single byte.
  53 class SingleByteXorCipher
  54         super Cipher
  55
  56         # Cryptographic key used in encryption and decryption.
  57         var key: Byte = 0.to_b
  58
  59         redef fun encrypt do
  60                 var key_bytes = new Bytes.with_capacity(1)
  61                 key_bytes.add(key)
  62                 ciphertext = plaintext.xorcipher(key_bytes)
  63         end
  64
  65         redef fun decrypt do
  66                 var key_bytes = new Bytes.with_capacity(1)
  67                 key_bytes.add(key)
  68                 plaintext = ciphertext.xorcipher(key_bytes)
  69         end
  70 end
  71
  72 # XOR cipher where the key is repeated to match the length of the message.
  73 class RepeatingKeyXorCipher
  74         super Cipher
  75
  76         # Cryptographic key used in encryption and decryption.
  77         var key = new Bytes.empty
  78
  79         redef fun encrypt do
  80                 assert key.length > 0
  81                 ciphertext = plaintext.xorcipher(key)
  82         end
  83
  84         redef fun decrypt do
  85                 assert key.length > 0
  86                 plaintext = ciphertext.xorcipher(key)
  87         end
  88 end