{
 "cells": [
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {},
   "outputs": [],
   "source": [
    "import os\n",
    "from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes\n",
    "from cryptography.hazmat import backends"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {},
   "outputs": [],
   "source": [
    "# Представление числа в виде битовой строки\n",
    "get_bin = lambda x, n: format(x, 'b').zfill(n)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {},
   "outputs": [],
   "source": [
    "# Представление массива чисел в виде битовой строки\n",
    "def byte_array_to_binary_string(array):\n",
    "    str_output = \"\"\n",
    "    for i in range(len(array)):\n",
    "        str_output += get_bin(array[i],8)\n",
    "    return str_output"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {},
   "outputs": [],
   "source": [
    "# Вычисление расстояние Хэмминга для строк из нулей и единиц\n",
    "def hamming_distance(str1, str2):\n",
    "    counter = 0\n",
    "    for i in range(min(len(str1),len(str2))):\n",
    "        if str1[i] != str2[i]:\n",
    "            counter += 1\n",
    "    return counter"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {},
   "outputs": [],
   "source": [
    "def xor_of_bytes_arrays(arr1, arr2):\n",
    "    xor_bytes = bytearray()\n",
    "    for i in range(min(len(arr1), len(arr2))):\n",
    "        xor_bytes.append(arr1[i] ^ arr2[i])\n",
    "    return xor_bytes"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "metadata": {},
   "outputs": [],
   "source": [
    "# Два открытых текста, отличающихся в одном бите\n",
    "# TODO: попробуйте использовать открытый текст длиной, не кратной размеру шифруемого блока. Объясните результат.\n",
    "plain_text1 = b\"a secret message\"\n",
    "plain_text2 = b\"c secret message\""
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "metadata": {
    "scrolled": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "01100001001000000111001101100101011000110111001001100101011101000010000001101101011001010111001101110011011000010110011101100101\n",
      "01100011001000000111001101100101011000110111001001100101011101000010000001101101011001010111001101110011011000010110011101100101\n",
      "Hamming distance =  1\n",
      "XORed plain texts =  00000010000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000\n"
     ]
    }
   ],
   "source": [
    "print(byte_array_to_binary_string(plain_text1))\n",
    "print(byte_array_to_binary_string(plain_text2))\n",
    "print(\"Hamming distance = \", hamming_distance(byte_array_to_binary_string(plain_text1), byte_array_to_binary_string(plain_text2)))\n",
    "print(\"XORed plain texts = \", byte_array_to_binary_string(bytes(xor_of_bytes_arrays(plain_text1, plain_text2))))"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 8,
   "metadata": {
    "scrolled": true
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Key =  01001000010100010111111001110010111001101010100110000101101101001101101110011111101111011010101100011110111010101101101000111010\n"
     ]
    }
   ],
   "source": [
    "# Генерация ключа длиной 128 бит. \n",
    "# TODO: попробуйте задать другую длину ключа. Объясните результат\n",
    "key = os.urandom(16)\n",
    "print(\"Key = \", byte_array_to_binary_string(key))\n",
    "cipher = Cipher(algorithms.AES(key), modes.ECB(), backend=backends.default_backend())\n",
    "encryptor1 = cipher.encryptor()\n",
    "encryptor2 = cipher.encryptor()\n",
    "decryptor1 = cipher.decryptor()\n",
    "decryptor2 = cipher.decryptor()\n",
    "decryptor3 = cipher.decryptor()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 9,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Cipher text's length =  16 , 16\n",
      "b'a secret message'\n"
     ]
    }
   ],
   "source": [
    "# Шифрование сообщений.\n",
    "# TODO: Почему для каждого сообщения используется свой экземпляр шифратора\n",
    "cipher_text1 = encryptor1.update(plain_text1) + encryptor1.finalize()\n",
    "cipher_text2 = encryptor2.update(plain_text2) + encryptor2.finalize()\n",
    "print(\"Cipher text's length = \", len(cipher_text1), \",\", len(cipher_text2))\n",
    "print(decryptor1.update(cipher_text1))"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 10,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "01111001011111110111001011000100111101101000011000011100010011111101111110100011100000110110000000011100011101010110110110101011\n",
      "10000010111001110010001101010111010010111111000110110011110010101100010001110101110110011001001110011010101010000000011100111111\n",
      "Hamming distance =  73\n"
     ]
    }
   ],
   "source": [
    "print(byte_array_to_binary_string(cipher_text1))\n",
    "print(byte_array_to_binary_string(cipher_text2))\n",
    "print(\"Hamming distance = \", hamming_distance(byte_array_to_binary_string(cipher_text1), byte_array_to_binary_string(cipher_text2)))"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 11,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "XORed cipher texts =  11111011100110000101000110010011101111010111011110101111100001010001101111010110010110101111001110000110110111010110101010010100\n"
     ]
    }
   ],
   "source": [
    "xored_cipher_text = bytes(xor_of_bytes_arrays(cipher_text1, cipher_text2))\n",
    "print(\"XORed cipher texts = \", byte_array_to_binary_string(xored_cipher_text))"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 17,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "b',\\xe1\\xbb\\xc1(Y\\xb6\\xa4\\x13\\xeb?\\xebC\\x18p8'\n"
     ]
    }
   ],
   "source": [
    "print(decryptor2.update(xored_cipher_text))"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 18,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "b'V\\x9e\\xa2i\\xaf^\\xf23\\x9c:\\xf3Q\\xed\\x03\\xa4\\x0b'\n"
     ]
    }
   ],
   "source": [
    "# Стравните (plain_text1) XOR (plain_text2) с результатом расшифрования decryptor2.update(xored_cipher_text). Объясните результат сравнения\n",
    "xored_plain_text = bytes(xor_of_bytes_arrays(plain_text1, plain_text2))\n",
    "print(decryptor1.update(xored_plain_text))"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": []
  }
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