Added renamed previous cipher to autokey stream cipher; added non-autokeyed version

diff --git a/SIGNED.md b/SIGNED.md
index fc950b99985ac52f902a657cfeff3f19d3e62606..7440f4d06e47cb7f6c522103c6fa3762457d0115 100644 (file)
--- a/SIGNED.md
+++ b/SIGNED.md
@@ -3,19 +3,19 @@
 -----BEGIN PGP SIGNATURE-----
 Version: GnuPG v2
 
-iQIcBAABAgAGBQJVuKYhAAoJEJPB2e07Pgbqj/0P/0XBNZk/zEPZUJrD9EqppzQU
-1m50EprHjaHFXBGGRMrExvpDgKljIR0KpId1wvmdkxmkQFASrr02+bs+YaEUp/Uv
-7+5GmJm6mHQbNzxQevOJUB4YqEF7rBjZAlSEZsSITNa/GRux1C9jEM71IId6ZEYv
-WIXU1lXgyue3tVk3jhv0lebzbyiea6wkFDdbMheQjDaY32g8Iyexo4qR4FWfUjmt
-nVaENg30ZOhvpY5CTGBLfAW35uUZIko9j87AFpQo2YyBBnH391rThJ3e3AL3hFtX
-fyVXFzbJDteYYAEVWET/p3vy+z4wKitJ1v8/o9kHYH4rPRehLGmNlKDFyeSGWI87
-R+m5ZXpZzXATz0Ydso9c1RCp1TgbB7byPyYDvyc92ND7jpdWJ/fH/ATTQggsRxx1
-88TMEMO77nXND4uQZcIRfdIQShUFtJy3F7PGmJ3SjtXHfvLAAqIFP3rwDeegRiiE
-T3yWzQEdM3JpU929xzCInPkJf3hQHUcuJdT1HcZBfySDpxAfVnLr9KYqxj/dpgGT
-YV+w8/D93hhnmArtgGSTSSsjTzJasQRo7/amEz/XiNn3408xJsGBghDXU80oyPfF
-lAbN05d/coqSfam5DEzK/LVvG5n3ghSSAFQKnDqgf2qtE82lC9WHzn1YrzunDcZt
-JQPSnePXSltPU//VuH8A
-=tV49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+=MWxD
 -----END PGP SIGNATURE-----
 
 ```
@@ -27,11 +27,12 @@ JQPSnePXSltPU//VuH8A
 #### Expect
 
 ```
-size   exec  file                         contents                                                        
-             ./                                                                                           
-384            .gitignore                 a93de2ae5c2a47a38599751d1f914566569dfa09dd1778e207117db6c71421dd
-28564          nim-menace-learning.ipynb  e13cd187b5785516ade802d71674ff682da7315da1a5ef82d2fe66d3ff8675bf
-9766           stream-cipher.ipynb        f02569456c91a825ea445c878b78341e83939444931affb15cded70c5c61d218
+size   exec  file                           contents                                                        
+             ./                                                                                             
+384            .gitignore                   a93de2ae5c2a47a38599751d1f914566569dfa09dd1778e207117db6c71421dd
+28564          nim-menace-learning.ipynb    e13cd187b5785516ade802d71674ff682da7315da1a5ef82d2fe66d3ff8675bf
+27883          stream-autokey-cipher.ipynb  dbd67c0f2cd1cc7470c3fc0fa17a1674ba69dab32068d8341be94891750173a6
+11503          stream-cipher.ipynb          8fa99343a3ce20abdf69645fe2baf0fe29551c619a77ff0556922884bbdc2658
 ```
 
 #### Ignore

diff --git a/stream-autokey-cipher.ipynb b/stream-autokey-cipher.ipynb
new file mode 100644 (file)
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
+}

diff --git a/stream-cipher.ipynb b/stream-cipher.ipynb
index 213eb834ee1cdf3d4207f0ef4036acb05bc990c3..21e9316c16fcdc90b7941224855693deb5e1efe8 100644 (file)
--- a/stream-cipher.ipynb
+++ b/stream-cipher.ipynb
@@ -8,12 +8,13 @@
    },
    "outputs": [],
    "source": [
-    "import string"
+    "import string\n",
+    "import itertools"
    ]
   },
   {
    "cell_type": "code",
-   "execution_count": 40,
+   "execution_count": 6,
    "metadata": {
     "collapsed": true
    },
@@ -25,7 +26,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 41,
+   "execution_count": 7,
    "metadata": {
     "collapsed": false
    },
@@ -36,7 +37,7 @@
        "'thequickbrownfoxjumpedoverthelzydoga'"
       ]
      },
-     "execution_count": 41,
+     "execution_count": 7,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -47,33 +48,33 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 2,
+   "execution_count": 12,
    "metadata": {
     "collapsed": false
    },
    "outputs": [],
    "source": [
-    "def encipher_letter(previous, current):\n",
-    "    new = (ord(previous) + ord(current) - 2 * ord('a')) % 26\n",
+    "def encipher_letter(key, current):\n",
+    "    new = (ord(key) + ord(current) - 2 * ord('a')) % 26\n",
     "    return chr(new + ord('a'))"
    ]
   },
   {
    "cell_type": "code",
-   "execution_count": 15,
+   "execution_count": 9,
    "metadata": {
     "collapsed": true
    },
    "outputs": [],
    "source": [
-    "def decipher_letter(previous, current):\n",
-    "    new = (ord(current) - ord(previous) - 2 * ord('a')) % 26\n",
+    "def decipher_letter(key, current):\n",
+    "    new = (ord(current) - ord(key)) % 26\n",
     "    return chr(new + ord('a'))"
    ]
   },
   {
    "cell_type": "code",
-   "execution_count": 4,
+   "execution_count": 13,
    "metadata": {
     "collapsed": false
    },
@@ -84,7 +85,7 @@
        "'a'"
       ]
      },
-     "execution_count": 4,
+     "execution_count": 13,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -95,7 +96,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 6,
+   "execution_count": 14,
    "metadata": {
     "collapsed": false
    },
@@ -106,7 +107,7 @@
        "'abcdefghijklmnopqrstuvwxyz'"
       ]
      },
-     "execution_count": 6,
+     "execution_count": 14,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -117,7 +118,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 7,
+   "execution_count": 15,
    "metadata": {
     "collapsed": false
    },
@@ -128,7 +129,7 @@
        "'bcdefghijklmnopqrstuvwxyza'"
       ]
      },
-     "execution_count": 7,
+     "execution_count": 15,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -139,7 +140,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 17,
+   "execution_count": 16,
    "metadata": {
     "collapsed": false
    },
@@ -150,7 +151,7 @@
        "'abcdefghijklmnopqrstuvwxyz'"
       ]
      },
-     "execution_count": 17,
+     "execution_count": 16,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -161,7 +162,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 18,
+   "execution_count": 17,
    "metadata": {
     "collapsed": false
    },
@@ -169,29 +170,43 @@
     {
      "data": {
       "text/plain": [
-       "'b'"
+       "'zabcdefghijklmnopqrstuvwxy'"
       ]
      },
-     "execution_count": 18,
+     "execution_count": 17,
      "metadata": {},
      "output_type": "execute_result"
     }
    ],
    "source": [
-    "decipher_letter('a', 'b')"
+    "''.join(decipher_letter('b', l) for l in string.ascii_lowercase)"
    ]
   },
   {
-   "cell_type": "markdown",
-   "metadata": {},
+   "cell_type": "code",
+   "execution_count": 18,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "'b'"
+      ]
+     },
+     "execution_count": 18,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
    "source": [
-    "e = (p + c) % 26\n",
-    "c = e - p"
+    "decipher_letter('a', 'b')"
    ]
   },
   {
    "cell_type": "code",
-   "execution_count": 20,
+   "execution_count": 19,
    "metadata": {
     "collapsed": false
    },
@@ -202,18 +217,20 @@
        "'abcdefghijklmnopqrstuvwxyzbcdefghijklmnopqrstuvwxyzacdefghijklmnopqrstuvwxyzabdefghijklmnopqrstuvwxyzabcefghijklmnopqrstuvwxyzabcdfghijklmnopqrstuvwxyzabcdeghijklmnopqrstuvwxyzabcdefhijklmnopqrstuvwxyzabcdefgijklmnopqrstuvwxyzabcdefghjklmnopqrstuvwxyzabcdefghiklmnopqrstuvwxyzabcdefghijlmnopqrstuvwxyzabcdefghijkmnopqrstuvwxyzabcdefghijklnopqrstuvwxyzabcdefghijklmopqrstuvwxyzabcdefghijklmnpqrstuvwxyzabcdefghijklmnoqrstuvwxyzabcdefghijklmnoprstuvwxyzabcdefghijklmnopqstuvwxyzabcdefghijklmnopqrtuvwxyzabcdefghijklmnopqrsuvwxyzabcdefghijklmnopqrstvwxyzabcdefghijklmnopqrstuwxyzabcdefghijklmnopqrstuvxyzabcdefghijklmnopqrstuvwyzabcdefghijklmnopqrstuvwxzabcdefghijklmnopqrstuvwxy'"
       ]
      },
-     "execution_count": 20,
+     "execution_count": 19,
      "metadata": {},
      "output_type": "execute_result"
     }
    ],
    "source": [
-    "''.join(encipher_letter(k, l) for l in string.ascii_lowercase for k in string.ascii_lowercase)"
+    "''.join(encipher_letter(k, l) \n",
+    "        for l in string.ascii_lowercase \n",
+    "        for k in string.ascii_lowercase)"
    ]
   },
   {
    "cell_type": "code",
-   "execution_count": 21,
+   "execution_count": 20,
    "metadata": {
     "collapsed": false
    },
@@ -233,19 +250,21 @@
        " ('j', 'a', 'j')]"
       ]
      },
-     "execution_count": 21,
+     "execution_count": 20,
      "metadata": {},
      "output_type": "execute_result"
     }
    ],
    "source": [
-    "encrypted = [(k, l, encipher_letter(k, l)) for l in string.ascii_lowercase for k in string.ascii_lowercase]\n",
+    "encrypted = [(k, l, encipher_letter(k, l)) \n",
+    "             for l in string.ascii_lowercase \n",
+    "             for k in string.ascii_lowercase]\n",
     "encrypted[:10]"
    ]
   },
   {
    "cell_type": "code",
-   "execution_count": 22,
+   "execution_count": 21,
    "metadata": {
     "collapsed": false
    },
@@ -256,7 +275,7 @@
        "True"
       ]
      },
-     "execution_count": 22,
+     "execution_count": 21,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -267,17 +286,18 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 55,
+   "execution_count": 32,
    "metadata": {
     "collapsed": true
    },
    "outputs": [],
    "source": [
-    "def encipher_message(plaintext, key='a'):\n",
+    "def encipher_message(plaintext, keystring='key'):\n",
+    "    key = itertools.cycle(keystring)\n",
     "    ciphertext = ''\n",
-    "    previous = key\n",
-    "    for letter in plaintext:\n",
-    "        cipherletter = encipher_letter(previous, letter)\n",
+    "    previous = keystring[0]\n",
+    "    for letter, keychar in zip(plaintext, key):\n",
+    "        cipherletter = encipher_letter(keychar, letter)\n",
     "        ciphertext += cipherletter\n",
     "        previous = cipherletter\n",
     "        # previous = letter\n",
@@ -286,7 +306,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 56,
+   "execution_count": 23,
    "metadata": {
     "collapsed": false
    },
@@ -294,21 +314,21 @@
     {
      "data": {
       "text/plain": [
-       "'hlwhv'"
+       "'hecoj'"
       ]
      },
-     "execution_count": 56,
+     "execution_count": 23,
      "metadata": {},
      "output_type": "execute_result"
     }
    ],
    "source": [
-    "encipher_message('hello')"
+    "encipher_message('hello', 'aardvark')"
    ]
   },
   {
    "cell_type": "code",
-   "execution_count": 57,
+   "execution_count": 24,
    "metadata": {
     "collapsed": false
    },
@@ -316,10 +336,10 @@
     {
      "data": {
       "text/plain": [
-       "'xbmxl'"
+       "'xubbe'"
       ]
      },
-     "execution_count": 57,
+     "execution_count": 24,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -330,17 +350,18 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 54,
+   "execution_count": 33,
    "metadata": {
     "collapsed": true
    },
    "outputs": [],
    "source": [
-    "def decipher_message(ciphertext, key='a'):\n",
+    "def decipher_message(ciphertext, keystring='key'):\n",
+    "    key = itertools.cycle(keystring)\n",
     "    plaintext = ''\n",
-    "    previous = key\n",
-    "    for letter in ciphertext:\n",
-    "        plainletter = decipher_letter(previous, letter)\n",
+    "    previous = keystring[0]\n",
+    "    for letter, keychar in zip(ciphertext, key):\n",
+    "        plainletter = decipher_letter(keychar, letter)\n",
     "        plaintext += plainletter\n",
     "        previous = letter\n",
     "        # previous = plainletter\n",
@@ -349,7 +370,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 58,
+   "execution_count": 27,
    "metadata": {
     "collapsed": false
    },
@@ -360,18 +381,18 @@
        "'hello'"
       ]
      },
-     "execution_count": 58,
+     "execution_count": 27,
      "metadata": {},
      "output_type": "execute_result"
     }
    ],
    "source": [
-    "decipher_message('hlwhv')"
+    "decipher_message('hecoj', 'aardvark')"
    ]
   },
   {
    "cell_type": "code",
-   "execution_count": 59,
+   "execution_count": 28,
    "metadata": {
     "collapsed": false
    },
@@ -379,21 +400,21 @@
     {
      "data": {
       "text/plain": [
-       "'xello'"
+       "'hello'"
       ]
      },
-     "execution_count": 59,
+     "execution_count": 28,
      "metadata": {},
      "output_type": "execute_result"
     }
    ],
    "source": [
-    "decipher_message('xbmxl')"
+    "decipher_message('xubbe', 'q')"
    ]
   },
   {
    "cell_type": "code",
-   "execution_count": 60,
+   "execution_count": 31,
    "metadata": {
     "collapsed": false
    },
@@ -401,21 +422,21 @@
     {
      "data": {
       "text/plain": [
-       "'hello'"
+       "'romyt'"
       ]
      },
-     "execution_count": 60,
+     "execution_count": 31,
      "metadata": {},
      "output_type": "execute_result"
     }
    ],
    "source": [
-    "decipher_message('xbmxl', 'q')"
+    "decipher_message('hecoj', 'q')"
    ]
   },
   {
    "cell_type": "code",
-   "execution_count": 61,
+   "execution_count": 34,
    "metadata": {
     "collapsed": false
    },
@@ -423,10 +444,10 @@
     {
      "data": {
       "text/plain": [
-       "'hlwhvjxlznbpdrfthvjxlznbpd'"
+       "'rijvsmysmysmysmysmysmysmys'"
       ]
      },
-     "execution_count": 61,
+     "execution_count": 34,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -437,7 +458,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 62,
+   "execution_count": 35,
    "metadata": {
     "collapsed": false
    },
@@ -448,13 +469,79 @@
        "'helloooooooooooooooooooooo'"
       ]
      },
-     "execution_count": 62,
+     "execution_count": 35,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "decipher_message('rijvsmysmysmysmysmysmysmys')"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 36,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "'qhiurlxrlxrlxrlxrlxrlxrlxr'"
+      ]
+     },
+     "execution_count": 36,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "decipher_message('rijvsmysmysmysmysmysmysmys', 'b')"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 37,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "'dlghpjalicxktzjayi'"
+      ]
+     },
+     "execution_count": 37,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "encipher_message(sanitised('This is a test message'), 'keyphrase')"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 38,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "'thisisatestmessage'"
+      ]
+     },
+     "execution_count": 38,
      "metadata": {},
      "output_type": "execute_result"
     }
    ],
    "source": [
-    "decipher_message('hlwhvjxlznbpdrfthvjxlznbpd')"
+    "decipher_message('dlghpjalicxktzjayi', 'keyphrase')"
    ]
   },
   {