X-Git-Url: https://git.njae.me.uk/?p=computing-unplugged-book.git;a=blobdiff_plain;f=stream-autokey-cipher.ipynb;fp=stream-autokey-cipher.ipynb;h=d102276652d6a653f463ed00bf349d3cbb7c0bb0;hp=0000000000000000000000000000000000000000;hb=4d73d2abd53cbbbfabc4f71c9243251a18268774;hpb=1cf9930f9655bba6e70d555ae408db8cde8289d5

diff --git a/stream-autokey-cipher.ipynb b/stream-autokey-cipher.ipynb
new file mode 100644
index 0000000..d102276
--- /dev/null
+++ b/stream-autokey-cipher.ipynb
@@ -0,0 +1,536 @@
+{
+ "cells": [
+  {
+   "cell_type": "code",
+   "execution_count": 1,
+   "metadata": {
+    "collapsed": true
+   },
+   "outputs": [],
+   "source": [
+    "import string\n",
+    "import itertools"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 2,
+   "metadata": {
+    "collapsed": true
+   },
+   "outputs": [],
+   "source": [
+    "def sanitised(text):\n",
+    "    return ''.join(letter.lower() for letter in text if letter in string.ascii_letters)"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 3,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "'thequickbrownfoxjumpedoverthelzydoga'"
+      ]
+     },
+     "execution_count": 3,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "sanitised('The quick brown fox! jumped OVER the l\\a!z%y* dog....a')"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 4,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [],
+   "source": [
+    "def encipher_letter(previous, key, current):\n",
+    "    new = (ord(previous) + ord(key) + ord(current) - 3 * ord('a')) % 26\n",
+    "    return chr(new + ord('a'))"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 17,
+   "metadata": {
+    "collapsed": true
+   },
+   "outputs": [],
+   "source": [
+    "def decipher_letter(previous, key, current):\n",
+    "    new = (ord(current) - ord(key) - ord(previous) + ord('a')) % 26\n",
+    "    return chr(new + ord('a'))"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 6,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "'a'"
+      ]
+     },
+     "execution_count": 6,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "encipher_letter('a', 'a', 'a')"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 8,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "'abcdefghijklmnopqrstuvwxyz'"
+      ]
+     },
+     "execution_count": 8,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "''.join(encipher_letter('a', 'a', l) for l in string.ascii_lowercase)"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 9,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "'cdefghijklmnopqrstuvwxyzab'"
+      ]
+     },
+     "execution_count": 9,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "''.join(encipher_letter('b', 'b', l) for l in string.ascii_lowercase)"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 18,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "'abcdefghijklmnopqrstuvwxyz'"
+      ]
+     },
+     "execution_count": 18,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "''.join(decipher_letter('a', 'a', l) for l in string.ascii_lowercase)"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 21,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "'yzabcdefghijklmnopqrstuvwx'"
+      ]
+     },
+     "execution_count": 21,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "''.join(decipher_letter('b', 'b', l) for l in string.ascii_lowercase)"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 20,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "'b'"
+      ]
+     },
+     "execution_count": 20,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "decipher_letter('a', 'a', 'b')"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 23,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       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+      ]
+     },
+     "execution_count": 23,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "''.join(encipher_letter(k, p, l) \n",
+    "        for l in string.ascii_lowercase \n",
+    "        for k in string.ascii_lowercase \n",
+    "        for p in string.ascii_lowercase)"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 24,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "[('a', 'a', 'a', 'a'),\n",
+       " ('a', 'b', 'a', 'b'),\n",
+       " ('a', 'c', 'a', 'c'),\n",
+       " ('a', 'd', 'a', 'd'),\n",
+       " ('a', 'e', 'a', 'e'),\n",
+       " ('a', 'f', 'a', 'f'),\n",
+       " ('a', 'g', 'a', 'g'),\n",
+       " ('a', 'h', 'a', 'h'),\n",
+       " ('a', 'i', 'a', 'i'),\n",
+       " ('a', 'j', 'a', 'j')]"
+      ]
+     },
+     "execution_count": 24,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "encrypted = [(k, p, l, encipher_letter(k, p, l)) \n",
+    "             for l in string.ascii_lowercase \n",
+    "             for k in string.ascii_lowercase\n",
+    "             for p in string.ascii_lowercase]\n",
+    "encrypted[:10]"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 25,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "True"
+      ]
+     },
+     "execution_count": 25,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "all(l == decipher_letter(k, p, e) for k, l, p, e in encrypted)"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 39,
+   "metadata": {
+    "collapsed": true
+   },
+   "outputs": [],
+   "source": [
+    "def encipher_message(plaintext, keystring='a'):\n",
+    "    key = itertools.cycle(keystring)\n",
+    "    ciphertext = ''\n",
+    "    previous = keystring[0]\n",
+    "    for letter, keychar in zip(plaintext, key):\n",
+    "        cipherletter = encipher_letter(previous, keychar, letter)\n",
+    "        ciphertext += cipherletter\n",
+    "        previous = cipherletter\n",
+    "        # previous = letter\n",
+    "    return ciphertext"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 40,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "'hlnbk'"
+      ]
+     },
+     "execution_count": 40,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "encipher_message('hello', 'aardvark')"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 41,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "'nhijn'"
+      ]
+     },
+     "execution_count": 41,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "encipher_message('hello', 'q')"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 42,
+   "metadata": {
+    "collapsed": true
+   },
+   "outputs": [],
+   "source": [
+    "def decipher_message(ciphertext, keystring='a'):\n",
+    "    key = itertools.cycle(keystring)\n",
+    "    plaintext = ''\n",
+    "    previous = keystring[0]\n",
+    "    for letter, keychar in zip(ciphertext, key):\n",
+    "        plainletter = decipher_letter(previous, keychar, letter)\n",
+    "        plaintext += plainletter\n",
+    "        previous = letter\n",
+    "        # previous = plainletter\n",
+    "    return plaintext"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 43,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "'hello'"
+      ]
+     },
+     "execution_count": 43,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "decipher_message('hlnbk', 'aardvark')"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 44,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "'hello'"
+      ]
+     },
+     "execution_count": 44,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "decipher_message('nhijn', 'q')"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 45,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "'hecoj'"
+      ]
+     },
+     "execution_count": 45,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "decipher_message('hlnbk')"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 46,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "'hlwhvjxlznbpdrfthvjxlznbpd'"
+      ]
+     },
+     "execution_count": 46,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "encipher_message('helloooooooooooooooooooooo')"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 47,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "'helloooooooooooooooooooooo'"
+      ]
+     },
+     "execution_count": 47,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "decipher_message('hlwhvjxlznbpdrfthvjxlznbpd')"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 48,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "'fdkknnnnnnnnnnnnnnnnnnnnnn'"
+      ]
+     },
+     "execution_count": 48,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "decipher_message('hlwhvjxlznbpdrfthvjxlznbpd', 'b')"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {
+    "collapsed": true
+   },
+   "outputs": [],
+   "source": []
+  }
+ ],
+ "metadata": {
+  "kernelspec": {
+   "display_name": "Python 3",
+   "language": "python",
+   "name": "python3"
+  },
+  "language_info": {
+   "codemirror_mode": {
+    "name": "ipython",
+    "version": 3
+   },
+   "file_extension": ".py",
+   "mimetype": "text/x-python",
+   "name": "python",
+   "nbconvert_exporter": "python",
+   "pygments_lexer": "ipython3",
+   "version": "3.4.2"
+  }
+ },
+ "nbformat": 4,
+ "nbformat_minor": 0
+}