Pw_wrong = Pdist(datafile('count_1w.txt'), lambda _k, N: log10(1/N))
Pl = Pdist(datafile('count_1l.txt'), lambda _k, _N: 0)
P2l = Pdist(datafile('count_2l.txt'), lambda _k, _N: 0)
+P3l = Pdist(datafile('count_3l.txt'), lambda _k, _N: 0)
def Pwords(words):
"""The Naive Bayes log probability of a sequence of words.
"""
return sum(P2l[p] for p in ngrams(letters, 2))
+def Ptrigrams(letters):
+ """The Naive Bayes log probability of the trigrams formed from a sequence
+ of letters.
+ """
+ return sum(P3l[p] for p in ngrams(letters, 3))
+
def cosine_similarity_score(text):
"""Finds the dissimilarity of a text to English, using the cosine distance
--- /dev/null
+<!DOCTYPE html>
+<html>
+ <head>
+ <title>Keyword ciphers</title>
+ <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"/>
+ <style type="text/css">
+ /* Slideshow styles */
+ body {
+ font-size: 20px;
+ }
+ h1, h2, h3 {
+ font-weight: 400;
+ margin-bottom: 0;
+ }
+ h1 { font-size: 3em; }
+ h2 { font-size: 2em; }
+ h3 { font-size: 1.6em; }
+ a, a > code {
+ text-decoration: none;
+ }
+ code {
+ -moz-border-radius: 5px;
+ -web-border-radius: 5px;
+ background: #e7e8e2;
+ border-radius: 5px;
+ font-size: 16px;
+ }
+ .plaintext {
+ background: #272822;
+ color: #80ff80;
+ text-shadow: 0 0 20px #333;
+ padding: 2px 5px;
+ }
+ .ciphertext {
+ background: #272822;
+ color: #ff6666;
+ text-shadow: 0 0 20px #333;
+ padding: 2px 5px;
+ }
+ .float-right {
+ float: right;
+ }
+ </style>
+ </head>
+ <body>
+ <textarea id="source">
+
+# Cipher programming training
+
+* [Aims](aims.html)
+* Caesar ciphers: [Making](caesar-encipher.html) and [Breaking](caesar-break.html)
+* Affine ciphers: [Making](affine-encipher.html) and [Breaking](affine-break.html)
+* [Word segmentation](word-segmentation.html)
+* Keyword ciphers: [Making](keyword-encipher.html) and [Breaking](keyword-break.html)
+* Transposition ciphers: [Making](transposition-encipher.html) and [Breaking](transposition-break.html)
+* [Alternative plausability scoring](alternative-plaintext-scoring.html)
+* [Further work](further-work.html)
+
+ </textarea>
+ <script src="http://gnab.github.io/remark/downloads/remark-0.6.0.min.js" type="text/javascript">
+ </script>
+
+ <script type="text/javascript"
+ src="http://cdn.mathjax.org/mathjax/latest/MathJax.js?config=TeX-AMS-MML_HTMLorMML&delayStartupUntil=configured"></script>
+
+ <script type="text/javascript">
+ var slideshow = remark.create({ ratio: "16:9" });
+
+ // Setup MathJax
+ MathJax.Hub.Config({
+ tex2jax: {
+ skipTags: ['script', 'noscript', 'style', 'textarea', 'pre']
+ }
+ });
+ MathJax.Hub.Queue(function() {
+ $(MathJax.Hub.getAllJax()).map(function(index, elem) {
+ return(elem.SourceElement());
+ }).parent().addClass('has-jax');
+ });
+ MathJax.Hub.Configured();
+ </script>
+ </body>
+</html>
--- /dev/null
+<!DOCTYPE html>
+<html>
+ <head>
+ <title>Keyword ciphers</title>
+ <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"/>
+ <style type="text/css">
+ /* Slideshow styles */
+ body {
+ font-size: 20px;
+ }
+ h1, h2, h3 {
+ font-weight: 400;
+ margin-bottom: 0;
+ }
+ h1 { font-size: 3em; }
+ h2 { font-size: 2em; }
+ h3 { font-size: 1.6em; }
+ a, a > code {
+ text-decoration: none;
+ }
+ code {
+ -moz-border-radius: 5px;
+ -web-border-radius: 5px;
+ background: #e7e8e2;
+ border-radius: 5px;
+ font-size: 16px;
+ }
+ .plaintext {
+ background: #272822;
+ color: #80ff80;
+ text-shadow: 0 0 20px #333;
+ padding: 2px 5px;
+ }
+ .ciphertext {
+ background: #272822;
+ color: #ff6666;
+ text-shadow: 0 0 20px #333;
+ padding: 2px 5px;
+ }
+ .float-right {
+ float: right;
+ }
+ </style>
+ </head>
+ <body>
+ <textarea id="source">
+
+# Breaking transposition ciphers
+
+ attack the fort at dawn
+
+ a t t a c
+ k t h e f
+ o r t a t
+ d a w n
+
+ akod ttra aean cft
+
+Generally quite familiar...
+
+## Try all the keys, pick the one that looks most like Englilsh
+
+---
+
+# ...Pick one that looks most like English
+
+But the naïve Bayes score will always be the same!
+
+* Same letters, just a different order.
+
+Score by probability of substrings of letters
+
+* Bigrams, trigrams, _n_-grams
+
+---
+
+# Finding _n_-grams
+
+Given `count_2l.txt` and `count_3l.txt`, counts of bigrams and trigrams in English
+
+# Write a function that returns all the _n_-grams for a text, given _n_
+ * Assume the text is already sanitised
+
+# Build `P2l`, `P3l` (after `Pl`), `Pbigrams`, `Ptrigrams` (after `Pletters`)
+
+---
+
+# Breaking scytale
+
+What are the possible keys?
+
+---
+
+# Try all the keys...
+
+*All* the keys?
+
+What's the transposition of 'cat'?
+
+* 'bat'?
+* 'car'?
+* 'wry'?
+* 'babe'?
+* 'powwow'?
+
+---
+
+# Equivalence classes and canonical forms
+
+Lots of words yield the same transposition
+
+* They're all in the same equivalence class
+* Only need to test one from the class
+
+General idea: if there are different ways to represent something, pick one to make comparisons easier
+
+* Canonical form, canonical representation
+
+---
+
+# Finding the transpositions to try
+
+```
+For each word:
+ if it's a new transposition:
+ add it to the list
+```
+
+What data structure to use to store the transpositions?
+
+
+ </textarea>
+ <script src="http://gnab.github.io/remark/downloads/remark-0.6.0.min.js" type="text/javascript">
+ </script>
+
+ <script type="text/javascript"
+ src="http://cdn.mathjax.org/mathjax/latest/MathJax.js?config=TeX-AMS-MML_HTMLorMML&delayStartupUntil=configured"></script>
+
+ <script type="text/javascript">
+ var slideshow = remark.create({ ratio: "16:9" });
+
+ // Setup MathJax
+ MathJax.Hub.Config({
+ tex2jax: {
+ skipTags: ['script', 'noscript', 'style', 'textarea', 'pre']
+ }
+ });
+ MathJax.Hub.Queue(function() {
+ $(MathJax.Hub.getAllJax()).map(function(index, elem) {
+ return(elem.SourceElement());
+ }).parent().addClass('has-jax');
+ });
+ MathJax.Hub.Configured();
+ </script>
+ </body>
+</html>
+
projects / cipher-training.git / commitdiff