
diff -r 5b5a68df6d16 -r e8ef8f38ca84 handouts/ho01.tex
--- a/handouts/ho01.tex	Mon Sep 15 09:36:02 2014 +0100
+++ b/handouts/ho01.tex	Sun Sep 21 11:46:49 2014 +0100
@@ -149,7 +149,7 @@
 regular expression matching in Python and in Ruby.
 
 \begin{center}
-\begin{tikzpicture}[y=.1cm, x=.15cm]
+\begin{tikzpicture}[y=.09cm, x=.15cm]
  	%axis
 	\draw (0,0) -- coordinate (x axis mid) (30,0);
    \draw (0,0) -- coordinate (y axis mid) (0,30);
@@ -184,18 +184,21 @@
 Ruby is even slightly worse.\footnote{In this example Ruby
 uses the slightly different regular expression
 \texttt{a?a?a?...a?a?aaa...aa}, where the \texttt{a?} and
-\texttt{a} each occur $n$ times.} Admittedly, this regular
-expression is carefully chosen to exhibit this exponential
-behaviour, but similar ones occur more often than one wants in
-``real life''. They are sometimes called \emph{evil regular
-expressions} because they have the potential to make regular
-expression matching engines to topple over, like in Python and
-Ruby. The problem with evil regular expressions is that they
-can have some serious consequences, for example, if you use
-them in your web-application. The reason is that hackers can
-look for these instances where the matching engine behaves
-badly and then mount a nice DoS-attack against your
-application.
+\texttt{a} each occur $n$ times. More test results can be
+found at \url{http://www.computerbytesman.com/redos/}.}
+Admittedly, this regular expression is carefully chosen to
+exhibit this exponential behaviour, but similar ones occur
+more often than one wants in ``real life''. They are sometimes
+called \emph{evil regular expressions} because they have the
+potential to make regular expression matching engines to
+topple over, like in Python and Ruby. The problem with evil
+regular expressions is that they can have some serious
+consequences, for example, if you use them in your
+web-application. The reason is that hackers can look for these
+instances where the matching engine behaves badly and then
+mount a nice DoS-attack against your application. These
+attacks are already have their own name: 
+\emph{Regular Expression Denial of Servive Attack (ReDoS)}.
 
 It will be instructive to look behind the ``scenes'' to find
 out why Python and Ruby (and others) behave so badly when
@@ -208,7 +211,7 @@
 up to 12,000 in less than 10(!) seconds, see the graph below:
 
 \begin{center}
-\begin{tikzpicture}[y=.1cm, x=.0006cm]
+\begin{tikzpicture}[y=.09cm, x=.0006cm]
  	%axis
 	\draw (0,0) -- coordinate (x axis mid) (12000,0);
    \draw (0,0) -- coordinate (y axis mid) (0,30);




