stream-cipher.ipynb

   1 {
   2  "cells": [
   3   {
   4    "cell_type": "code",
   5    "execution_count": 5,
   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": 6,
  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": 7,
  30    "metadata": {
  31     "collapsed": false
  32    },
  33    "outputs": [
  34     {
  35      "data": {
  36       "text/plain": [
  37        "'thequickbrownfoxjumpedoverthelzydoga'"
  38       ]
  39      },
  40      "execution_count": 7,
  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": 12,
  52    "metadata": {
  53     "collapsed": false
  54    },
  55    "outputs": [],
  56    "source": [
  57     "def encipher_letter(key, current):\n",
  58     "    new = (ord(key) + ord(current) - 2 * ord('a')) % 26\n",
  59     "    return chr(new + ord('a'))"
  60    ]
  61   },
  62   {
  63    "cell_type": "code",
  64    "execution_count": 9,
  65    "metadata": {
  66     "collapsed": true
  67    },
  68    "outputs": [],
  69    "source": [
  70     "def decipher_letter(key, current):\n",
  71     "    new = (ord(current) - ord(key)) % 26\n",
  72     "    return chr(new + ord('a'))"
  73    ]
  74   },
  75   {
  76    "cell_type": "code",
  77    "execution_count": 13,
  78    "metadata": {
  79     "collapsed": false
  80    },
  81    "outputs": [
  82     {
  83      "data": {
  84       "text/plain": [
  85        "'a'"
  86       ]
  87      },
  88      "execution_count": 13,
  89      "metadata": {},
  90      "output_type": "execute_result"
  91     }
  92    ],
  93    "source": [
  94     "encipher_letter('a', 'a')"
  95    ]
  96   },
  97   {
  98    "cell_type": "code",
  99    "execution_count": 14,
 100    "metadata": {
 101     "collapsed": false
 102    },
 103    "outputs": [
 104     {
 105      "data": {
 106       "text/plain": [
 107        "'abcdefghijklmnopqrstuvwxyz'"
 108       ]
 109      },
 110      "execution_count": 14,
 111      "metadata": {},
 112      "output_type": "execute_result"
 113     }
 114    ],
 115    "source": [
 116     "''.join(encipher_letter('a', l) for l in string.ascii_lowercase)"
 117    ]
 118   },
 119   {
 120    "cell_type": "code",
 121    "execution_count": 15,
 122    "metadata": {
 123     "collapsed": false
 124    },
 125    "outputs": [
 126     {
 127      "data": {
 128       "text/plain": [
 129        "'bcdefghijklmnopqrstuvwxyza'"
 130       ]
 131      },
 132      "execution_count": 15,
 133      "metadata": {},
 134      "output_type": "execute_result"
 135     }
 136    ],
 137    "source": [
 138     "''.join(encipher_letter('b', l) for l in string.ascii_lowercase)"
 139    ]
 140   },
 141   {
 142    "cell_type": "code",
 143    "execution_count": 16,
 144    "metadata": {
 145     "collapsed": false
 146    },
 147    "outputs": [
 148     {
 149      "data": {
 150       "text/plain": [
 151        "'abcdefghijklmnopqrstuvwxyz'"
 152       ]
 153      },
 154      "execution_count": 16,
 155      "metadata": {},
 156      "output_type": "execute_result"
 157     }
 158    ],
 159    "source": [
 160     "''.join(decipher_letter('a', l) for l in string.ascii_lowercase)"
 161    ]
 162   },
 163   {
 164    "cell_type": "code",
 165    "execution_count": 17,
 166    "metadata": {
 167     "collapsed": false
 168    },
 169    "outputs": [
 170     {
 171      "data": {
 172       "text/plain": [
 173        "'zabcdefghijklmnopqrstuvwxy'"
 174       ]
 175      },
 176      "execution_count": 17,
 177      "metadata": {},
 178      "output_type": "execute_result"
 179     }
 180    ],
 181    "source": [
 182     "''.join(decipher_letter('b', l) for l in string.ascii_lowercase)"
 183    ]
 184   },
 185   {
 186    "cell_type": "code",
 187    "execution_count": 18,
 188    "metadata": {
 189     "collapsed": false
 190    },
 191    "outputs": [
 192     {
 193      "data": {
 194       "text/plain": [
 195        "'b'"
 196       ]
 197      },
 198      "execution_count": 18,
 199      "metadata": {},
 200      "output_type": "execute_result"
 201     }
 202    ],
 203    "source": [
 204     "decipher_letter('a', 'b')"
 205    ]
 206   },
 207   {
 208    "cell_type": "code",
 209    "execution_count": 19,
 210    "metadata": {
 211     "collapsed": false
 212    },
 213    "outputs": [
 214     {
 215      "data": {
 216       "text/plain": [
 217        "'abcdefghijklmnopqrstuvwxyzbcdefghijklmnopqrstuvwxyzacdefghijklmnopqrstuvwxyzabdefghijklmnopqrstuvwxyzabcefghijklmnopqrstuvwxyzabcdfghijklmnopqrstuvwxyzabcdeghijklmnopqrstuvwxyzabcdefhijklmnopqrstuvwxyzabcdefgijklmnopqrstuvwxyzabcdefghjklmnopqrstuvwxyzabcdefghiklmnopqrstuvwxyzabcdefghijlmnopqrstuvwxyzabcdefghijkmnopqrstuvwxyzabcdefghijklnopqrstuvwxyzabcdefghijklmopqrstuvwxyzabcdefghijklmnpqrstuvwxyzabcdefghijklmnoqrstuvwxyzabcdefghijklmnoprstuvwxyzabcdefghijklmnopqstuvwxyzabcdefghijklmnopqrtuvwxyzabcdefghijklmnopqrsuvwxyzabcdefghijklmnopqrstvwxyzabcdefghijklmnopqrstuwxyzabcdefghijklmnopqrstuvxyzabcdefghijklmnopqrstuvwyzabcdefghijklmnopqrstuvwxzabcdefghijklmnopqrstuvwxy'"
 218       ]
 219      },
 220      "execution_count": 19,
 221      "metadata": {},
 222      "output_type": "execute_result"
 223     }
 224    ],
 225    "source": [
 226     "''.join(encipher_letter(k, l) \n",
 227     "        for l in string.ascii_lowercase \n",
 228     "        for k in string.ascii_lowercase)"
 229    ]
 230   },
 231   {
 232    "cell_type": "code",
 233    "execution_count": 20,
 234    "metadata": {
 235     "collapsed": false
 236    },
 237    "outputs": [
 238     {
 239      "data": {
 240       "text/plain": [
 241        "[('a', 'a', 'a'),\n",
 242        " ('b', 'a', 'b'),\n",
 243        " ('c', 'a', 'c'),\n",
 244        " ('d', 'a', 'd'),\n",
 245        " ('e', 'a', 'e'),\n",
 246        " ('f', 'a', 'f'),\n",
 247        " ('g', 'a', 'g'),\n",
 248        " ('h', 'a', 'h'),\n",
 249        " ('i', 'a', 'i'),\n",
 250        " ('j', 'a', 'j')]"
 251       ]
 252      },
 253      "execution_count": 20,
 254      "metadata": {},
 255      "output_type": "execute_result"
 256     }
 257    ],
 258    "source": [
 259     "encrypted = [(k, l, encipher_letter(k, l)) \n",
 260     "             for l in string.ascii_lowercase \n",
 261     "             for k in string.ascii_lowercase]\n",
 262     "encrypted[:10]"
 263    ]
 264   },
 265   {
 266    "cell_type": "code",
 267    "execution_count": 21,
 268    "metadata": {
 269     "collapsed": false
 270    },
 271    "outputs": [
 272     {
 273      "data": {
 274       "text/plain": [
 275        "True"
 276       ]
 277      },
 278      "execution_count": 21,
 279      "metadata": {},
 280      "output_type": "execute_result"
 281     }
 282    ],
 283    "source": [
 284     "all(l == decipher_letter(k, e) for k, l, e in encrypted)"
 285    ]
 286   },
 287   {
 288    "cell_type": "code",
 289    "execution_count": 32,
 290    "metadata": {
 291     "collapsed": true
 292    },
 293    "outputs": [],
 294    "source": [
 295     "def encipher_message(plaintext, keystring='key'):\n",
 296     "    key = itertools.cycle(keystring)\n",
 297     "    ciphertext = ''\n",
 298     "    previous = keystring[0]\n",
 299     "    for letter, keychar in zip(plaintext, key):\n",
 300     "        cipherletter = encipher_letter(keychar, letter)\n",
 301     "        ciphertext += cipherletter\n",
 302     "        previous = cipherletter\n",
 303     "        # previous = letter\n",
 304     "    return ciphertext"
 305    ]
 306   },
 307   {
 308    "cell_type": "code",
 309    "execution_count": 23,
 310    "metadata": {
 311     "collapsed": false
 312    },
 313    "outputs": [
 314     {
 315      "data": {
 316       "text/plain": [
 317        "'hecoj'"
 318       ]
 319      },
 320      "execution_count": 23,
 321      "metadata": {},
 322      "output_type": "execute_result"
 323     }
 324    ],
 325    "source": [
 326     "encipher_message('hello', 'aardvark')"
 327    ]
 328   },
 329   {
 330    "cell_type": "code",
 331    "execution_count": 24,
 332    "metadata": {
 333     "collapsed": false
 334    },
 335    "outputs": [
 336     {
 337      "data": {
 338       "text/plain": [
 339        "'xubbe'"
 340       ]
 341      },
 342      "execution_count": 24,
 343      "metadata": {},
 344      "output_type": "execute_result"
 345     }
 346    ],
 347    "source": [
 348     "encipher_message('hello', 'q')"
 349    ]
 350   },
 351   {
 352    "cell_type": "code",
 353    "execution_count": 33,
 354    "metadata": {
 355     "collapsed": true
 356    },
 357    "outputs": [],
 358    "source": [
 359     "def decipher_message(ciphertext, keystring='key'):\n",
 360     "    key = itertools.cycle(keystring)\n",
 361     "    plaintext = ''\n",
 362     "    previous = keystring[0]\n",
 363     "    for letter, keychar in zip(ciphertext, key):\n",
 364     "        plainletter = decipher_letter(keychar, letter)\n",
 365     "        plaintext += plainletter\n",
 366     "        previous = letter\n",
 367     "        # previous = plainletter\n",
 368     "    return plaintext"
 369    ]
 370   },
 371   {
 372    "cell_type": "code",
 373    "execution_count": 27,
 374    "metadata": {
 375     "collapsed": false
 376    },
 377    "outputs": [
 378     {
 379      "data": {
 380       "text/plain": [
 381        "'hello'"
 382       ]
 383      },
 384      "execution_count": 27,
 385      "metadata": {},
 386      "output_type": "execute_result"
 387     }
 388    ],
 389    "source": [
 390     "decipher_message('hecoj', 'aardvark')"
 391    ]
 392   },
 393   {
 394    "cell_type": "code",
 395    "execution_count": 28,
 396    "metadata": {
 397     "collapsed": false
 398    },
 399    "outputs": [
 400     {
 401      "data": {
 402       "text/plain": [
 403        "'hello'"
 404       ]
 405      },
 406      "execution_count": 28,
 407      "metadata": {},
 408      "output_type": "execute_result"
 409     }
 410    ],
 411    "source": [
 412     "decipher_message('xubbe', 'q')"
 413    ]
 414   },
 415   {
 416    "cell_type": "code",
 417    "execution_count": 31,
 418    "metadata": {
 419     "collapsed": false
 420    },
 421    "outputs": [
 422     {
 423      "data": {
 424       "text/plain": [
 425        "'romyt'"
 426       ]
 427      },
 428      "execution_count": 31,
 429      "metadata": {},
 430      "output_type": "execute_result"
 431     }
 432    ],
 433    "source": [
 434     "decipher_message('hecoj', 'q')"
 435    ]
 436   },
 437   {
 438    "cell_type": "code",
 439    "execution_count": 34,
 440    "metadata": {
 441     "collapsed": false
 442    },
 443    "outputs": [
 444     {
 445      "data": {
 446       "text/plain": [
 447        "'rijvsmysmysmysmysmysmysmys'"
 448       ]
 449      },
 450      "execution_count": 34,
 451      "metadata": {},
 452      "output_type": "execute_result"
 453     }
 454    ],
 455    "source": [
 456     "encipher_message('helloooooooooooooooooooooo')"
 457    ]
 458   },
 459   {
 460    "cell_type": "code",
 461    "execution_count": 35,
 462    "metadata": {
 463     "collapsed": false
 464    },
 465    "outputs": [
 466     {
 467      "data": {
 468       "text/plain": [
 469        "'helloooooooooooooooooooooo'"
 470       ]
 471      },
 472      "execution_count": 35,
 473      "metadata": {},
 474      "output_type": "execute_result"
 475     }
 476    ],
 477    "source": [
 478     "decipher_message('rijvsmysmysmysmysmysmysmys')"
 479    ]
 480   },
 481   {
 482    "cell_type": "code",
 483    "execution_count": 36,
 484    "metadata": {
 485     "collapsed": false
 486    },
 487    "outputs": [
 488     {
 489      "data": {
 490       "text/plain": [
 491        "'qhiurlxrlxrlxrlxrlxrlxrlxr'"
 492       ]
 493      },
 494      "execution_count": 36,
 495      "metadata": {},
 496      "output_type": "execute_result"
 497     }
 498    ],
 499    "source": [
 500     "decipher_message('rijvsmysmysmysmysmysmysmys', 'b')"
 501    ]
 502   },
 503   {
 504    "cell_type": "code",
 505    "execution_count": 37,
 506    "metadata": {
 507     "collapsed": false
 508    },
 509    "outputs": [
 510     {
 511      "data": {
 512       "text/plain": [
 513        "'dlghpjalicxktzjayi'"
 514       ]
 515      },
 516      "execution_count": 37,
 517      "metadata": {},
 518      "output_type": "execute_result"
 519     }
 520    ],
 521    "source": [
 522     "encipher_message(sanitised('This is a test message'), 'keyphrase')"
 523    ]
 524   },
 525   {
 526    "cell_type": "code",
 527    "execution_count": 38,
 528    "metadata": {
 529     "collapsed": false
 530    },
 531    "outputs": [
 532     {
 533      "data": {
 534       "text/plain": [
 535        "'thisisatestmessage'"
 536       ]
 537      },
 538      "execution_count": 38,
 539      "metadata": {},
 540      "output_type": "execute_result"
 541     }
 542    ],
 543    "source": [
 544     "decipher_message('dlghpjalicxktzjayi', 'keyphrase')"
 545    ]
 546   },
 547   {
 548    "cell_type": "code",
 549    "execution_count": null,
 550    "metadata": {
 551     "collapsed": true
 552    },
 553    "outputs": [],
 554    "source": []
 555   }
 556  ],
 557  "metadata": {
 558   "kernelspec": {
 559    "display_name": "Python 3",
 560    "language": "python",
 561    "name": "python3"
 562   },
 563   "language_info": {
 564    "codemirror_mode": {
 565     "name": "ipython",
 566     "version": 3
 567    },
 568    "file_extension": ".py",
 569    "mimetype": "text/x-python",
 570    "name": "python",
 571    "nbconvert_exporter": "python",
 572    "pygments_lexer": "ipython3",
 573    "version": "3.4.2"
 574   }
 575  },
 576  "nbformat": 4,
 577  "nbformat_minor": 0
 578 }