stream-autokey-cipher.ipynb

   1 {
   2  "cells": [
   3   {
   4    "cell_type": "code",
   5    "execution_count": 1,
   6    "metadata": {
   7     "collapsed": true
   8    },
   9    "outputs": [],
  10    "source": [
  11     "import string\n",
  12     "import itertools"
  13    ]
  14   },
  15   {
  16    "cell_type": "code",
  17    "execution_count": 2,
  18    "metadata": {
  19     "collapsed": true
  20    },
  21    "outputs": [],
  22    "source": [
  23     "def sanitised(text):\n",
  24     "    return ''.join(letter.lower() for letter in text if letter in string.ascii_letters)"
  25    ]
  26   },
  27   {
  28    "cell_type": "code",
  29    "execution_count": 3,
  30    "metadata": {
  31     "collapsed": false
  32    },
  33    "outputs": [
  34     {
  35      "data": {
  36       "text/plain": [
  37        "'thequickbrownfoxjumpedoverthelzydoga'"
  38       ]
  39      },
  40      "execution_count": 3,
  41      "metadata": {},
  42      "output_type": "execute_result"
  43     }
  44    ],
  45    "source": [
  46     "sanitised('The quick brown fox! jumped OVER the l\\a!z%y* dog....a')"
  47    ]
  48   },
  49   {
  50    "cell_type": "code",
  51    "execution_count": 4,
  52    "metadata": {
  53     "collapsed": false
  54    },
  55    "outputs": [],
  56    "source": [
  57     "def encipher_letter(previous, key, current):\n",
  58     "    new = (ord(previous) + ord(key) + ord(current) - 3 * ord('a')) % 26\n",
  59     "    return chr(new + ord('a'))"
  60    ]
  61   },
  62   {
  63    "cell_type": "code",
  64    "execution_count": 17,
  65    "metadata": {
  66     "collapsed": true
  67    },
  68    "outputs": [],
  69    "source": [
  70     "def decipher_letter(previous, key, current):\n",
  71     "    new = (ord(current) - ord(key) - ord(previous) + ord('a')) % 26\n",
  72     "    return chr(new + ord('a'))"
  73    ]
  74   },
  75   {
  76    "cell_type": "code",
  77    "execution_count": 6,
  78    "metadata": {
  79     "collapsed": false
  80    },
  81    "outputs": [
  82     {
  83      "data": {
  84       "text/plain": [
  85        "'a'"
  86       ]
  87      },
  88      "execution_count": 6,
  89      "metadata": {},
  90      "output_type": "execute_result"
  91     }
  92    ],
  93    "source": [
  94     "encipher_letter('a', 'a', 'a')"
  95    ]
  96   },
  97   {
  98    "cell_type": "code",
  99    "execution_count": 8,
 100    "metadata": {
 101     "collapsed": false
 102    },
 103    "outputs": [
 104     {
 105      "data": {
 106       "text/plain": [
 107        "'abcdefghijklmnopqrstuvwxyz'"
 108       ]
 109      },
 110      "execution_count": 8,
 111      "metadata": {},
 112      "output_type": "execute_result"
 113     }
 114    ],
 115    "source": [
 116     "''.join(encipher_letter('a', 'a', l) for l in string.ascii_lowercase)"
 117    ]
 118   },
 119   {
 120    "cell_type": "code",
 121    "execution_count": 9,
 122    "metadata": {
 123     "collapsed": false
 124    },
 125    "outputs": [
 126     {
 127      "data": {
 128       "text/plain": [
 129        "'cdefghijklmnopqrstuvwxyzab'"
 130       ]
 131      },
 132      "execution_count": 9,
 133      "metadata": {},
 134      "output_type": "execute_result"
 135     }
 136    ],
 137    "source": [
 138     "''.join(encipher_letter('b', 'b', l) for l in string.ascii_lowercase)"
 139    ]
 140   },
 141   {
 142    "cell_type": "code",
 143    "execution_count": 18,
 144    "metadata": {
 145     "collapsed": false
 146    },
 147    "outputs": [
 148     {
 149      "data": {
 150       "text/plain": [
 151        "'abcdefghijklmnopqrstuvwxyz'"
 152       ]
 153      },
 154      "execution_count": 18,
 155      "metadata": {},
 156      "output_type": "execute_result"
 157     }
 158    ],
 159    "source": [
 160     "''.join(decipher_letter('a', 'a', l) for l in string.ascii_lowercase)"
 161    ]
 162   },
 163   {
 164    "cell_type": "code",
 165    "execution_count": 21,
 166    "metadata": {
 167     "collapsed": false
 168    },
 169    "outputs": [
 170     {
 171      "data": {
 172       "text/plain": [
 173        "'yzabcdefghijklmnopqrstuvwx'"
 174       ]
 175      },
 176      "execution_count": 21,
 177      "metadata": {},
 178      "output_type": "execute_result"
 179     }
 180    ],
 181    "source": [
 182     "''.join(decipher_letter('b', 'b', l) for l in string.ascii_lowercase)"
 183    ]
 184   },
 185   {
 186    "cell_type": "code",
 187    "execution_count": 20,
 188    "metadata": {
 189     "collapsed": false
 190    },
 191    "outputs": [
 192     {
 193      "data": {
 194       "text/plain": [
 195        "'b'"
 196       ]
 197      },
 198      "execution_count": 20,
 199      "metadata": {},
 200      "output_type": "execute_result"
 201     }
 202    ],
 203    "source": [
 204     "decipher_letter('a', 'a', 'b')"
 205    ]
 206   },
 207   {
 208    "cell_type": "code",
 209    "execution_count": 23,
 210    "metadata": {
 211     "collapsed": false
 212    },
 213    "outputs": [
 214     {
 215      "data": {
 216       "text/plain": [
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 218       ]
 219      },
 220      "execution_count": 23,
 221      "metadata": {},
 222      "output_type": "execute_result"
 223     }
 224    ],
 225    "source": [
 226     "''.join(encipher_letter(k, p, l) \n",
 227     "        for l in string.ascii_lowercase \n",
 228     "        for k in string.ascii_lowercase \n",
 229     "        for p in string.ascii_lowercase)"
 230    ]
 231   },
 232   {
 233    "cell_type": "code",
 234    "execution_count": 24,
 235    "metadata": {
 236     "collapsed": false
 237    },
 238    "outputs": [
 239     {
 240      "data": {
 241       "text/plain": [
 242        "[('a', 'a', 'a', 'a'),\n",
 243        " ('a', 'b', 'a', 'b'),\n",
 244        " ('a', 'c', 'a', 'c'),\n",
 245        " ('a', 'd', 'a', 'd'),\n",
 246        " ('a', 'e', 'a', 'e'),\n",
 247        " ('a', 'f', 'a', 'f'),\n",
 248        " ('a', 'g', 'a', 'g'),\n",
 249        " ('a', 'h', 'a', 'h'),\n",
 250        " ('a', 'i', 'a', 'i'),\n",
 251        " ('a', 'j', 'a', 'j')]"
 252       ]
 253      },
 254      "execution_count": 24,
 255      "metadata": {},
 256      "output_type": "execute_result"
 257     }
 258    ],
 259    "source": [
 260     "encrypted = [(k, p, l, encipher_letter(k, p, l)) \n",
 261     "             for l in string.ascii_lowercase \n",
 262     "             for k in string.ascii_lowercase\n",
 263     "             for p in string.ascii_lowercase]\n",
 264     "encrypted[:10]"
 265    ]
 266   },
 267   {
 268    "cell_type": "code",
 269    "execution_count": 25,
 270    "metadata": {
 271     "collapsed": false
 272    },
 273    "outputs": [
 274     {
 275      "data": {
 276       "text/plain": [
 277        "True"
 278       ]
 279      },
 280      "execution_count": 25,
 281      "metadata": {},
 282      "output_type": "execute_result"
 283     }
 284    ],
 285    "source": [
 286     "all(l == decipher_letter(k, p, e) for k, l, p, e in encrypted)"
 287    ]
 288   },
 289   {
 290    "cell_type": "code",
 291    "execution_count": 39,
 292    "metadata": {
 293     "collapsed": true
 294    },
 295    "outputs": [],
 296    "source": [
 297     "def encipher_message(plaintext, keystring='a'):\n",
 298     "    key = itertools.cycle(keystring)\n",
 299     "    ciphertext = ''\n",
 300     "    previous = keystring[0]\n",
 301     "    for letter, keychar in zip(plaintext, key):\n",
 302     "        cipherletter = encipher_letter(previous, keychar, letter)\n",
 303     "        ciphertext += cipherletter\n",
 304     "        previous = cipherletter\n",
 305     "        # previous = letter\n",
 306     "    return ciphertext"
 307    ]
 308   },
 309   {
 310    "cell_type": "code",
 311    "execution_count": 40,
 312    "metadata": {
 313     "collapsed": false
 314    },
 315    "outputs": [
 316     {
 317      "data": {
 318       "text/plain": [
 319        "'hlnbk'"
 320       ]
 321      },
 322      "execution_count": 40,
 323      "metadata": {},
 324      "output_type": "execute_result"
 325     }
 326    ],
 327    "source": [
 328     "encipher_message('hello', 'aardvark')"
 329    ]
 330   },
 331   {
 332    "cell_type": "code",
 333    "execution_count": 41,
 334    "metadata": {
 335     "collapsed": false
 336    },
 337    "outputs": [
 338     {
 339      "data": {
 340       "text/plain": [
 341        "'nhijn'"
 342       ]
 343      },
 344      "execution_count": 41,
 345      "metadata": {},
 346      "output_type": "execute_result"
 347     }
 348    ],
 349    "source": [
 350     "encipher_message('hello', 'q')"
 351    ]
 352   },
 353   {
 354    "cell_type": "code",
 355    "execution_count": 42,
 356    "metadata": {
 357     "collapsed": true
 358    },
 359    "outputs": [],
 360    "source": [
 361     "def decipher_message(ciphertext, keystring='a'):\n",
 362     "    key = itertools.cycle(keystring)\n",
 363     "    plaintext = ''\n",
 364     "    previous = keystring[0]\n",
 365     "    for letter, keychar in zip(ciphertext, key):\n",
 366     "        plainletter = decipher_letter(previous, keychar, letter)\n",
 367     "        plaintext += plainletter\n",
 368     "        previous = letter\n",
 369     "        # previous = plainletter\n",
 370     "    return plaintext"
 371    ]
 372   },
 373   {
 374    "cell_type": "code",
 375    "execution_count": 43,
 376    "metadata": {
 377     "collapsed": false
 378    },
 379    "outputs": [
 380     {
 381      "data": {
 382       "text/plain": [
 383        "'hello'"
 384       ]
 385      },
 386      "execution_count": 43,
 387      "metadata": {},
 388      "output_type": "execute_result"
 389     }
 390    ],
 391    "source": [
 392     "decipher_message('hlnbk', 'aardvark')"
 393    ]
 394   },
 395   {
 396    "cell_type": "code",
 397    "execution_count": 44,
 398    "metadata": {
 399     "collapsed": false
 400    },
 401    "outputs": [
 402     {
 403      "data": {
 404       "text/plain": [
 405        "'hello'"
 406       ]
 407      },
 408      "execution_count": 44,
 409      "metadata": {},
 410      "output_type": "execute_result"
 411     }
 412    ],
 413    "source": [
 414     "decipher_message('nhijn', 'q')"
 415    ]
 416   },
 417   {
 418    "cell_type": "code",
 419    "execution_count": 45,
 420    "metadata": {
 421     "collapsed": false
 422    },
 423    "outputs": [
 424     {
 425      "data": {
 426       "text/plain": [
 427        "'hecoj'"
 428       ]
 429      },
 430      "execution_count": 45,
 431      "metadata": {},
 432      "output_type": "execute_result"
 433     }
 434    ],
 435    "source": [
 436     "decipher_message('hlnbk')"
 437    ]
 438   },
 439   {
 440    "cell_type": "code",
 441    "execution_count": 46,
 442    "metadata": {
 443     "collapsed": false
 444    },
 445    "outputs": [
 446     {
 447      "data": {
 448       "text/plain": [
 449        "'hlwhvjxlznbpdrfthvjxlznbpd'"
 450       ]
 451      },
 452      "execution_count": 46,
 453      "metadata": {},
 454      "output_type": "execute_result"
 455     }
 456    ],
 457    "source": [
 458     "encipher_message('helloooooooooooooooooooooo')"
 459    ]
 460   },
 461   {
 462    "cell_type": "code",
 463    "execution_count": 47,
 464    "metadata": {
 465     "collapsed": false
 466    },
 467    "outputs": [
 468     {
 469      "data": {
 470       "text/plain": [
 471        "'helloooooooooooooooooooooo'"
 472       ]
 473      },
 474      "execution_count": 47,
 475      "metadata": {},
 476      "output_type": "execute_result"
 477     }
 478    ],
 479    "source": [
 480     "decipher_message('hlwhvjxlznbpdrfthvjxlznbpd')"
 481    ]
 482   },
 483   {
 484    "cell_type": "code",
 485    "execution_count": 48,
 486    "metadata": {
 487     "collapsed": false
 488    },
 489    "outputs": [
 490     {
 491      "data": {
 492       "text/plain": [
 493        "'fdkknnnnnnnnnnnnnnnnnnnnnn'"
 494       ]
 495      },
 496      "execution_count": 48,
 497      "metadata": {},
 498      "output_type": "execute_result"
 499     }
 500    ],
 501    "source": [
 502     "decipher_message('hlwhvjxlznbpdrfthvjxlznbpd', 'b')"
 503    ]
 504   },
 505   {
 506    "cell_type": "code",
 507    "execution_count": null,
 508    "metadata": {
 509     "collapsed": true
 510    },
 511    "outputs": [],
 512    "source": []
 513   }
 514  ],
 515  "metadata": {
 516   "kernelspec": {
 517    "display_name": "Python 3",
 518    "language": "python",
 519    "name": "python3"
 520   },
 521   "language_info": {
 522    "codemirror_mode": {
 523     "name": "ipython",
 524     "version": 3
 525    },
 526    "file_extension": ".py",
 527    "mimetype": "text/x-python",
 528    "name": "python",
 529    "nbconvert_exporter": "python",
 530    "pygments_lexer": "ipython3",
 531    "version": "3.4.2"
 532   }
 533  },
 534  "nbformat": 4,
 535  "nbformat_minor": 0
 536 }