61 <p>The background for this project is that some regular expressions are |
61 <p>The background for this project is that some regular expressions are |
62 “<A HREF="http://en.wikipedia.org/wiki/ReDoS#Examples">evil</A>” |
62 “<A HREF="http://en.wikipedia.org/wiki/ReDoS#Examples">evil</A>” |
63 and can “stab you in the back” according to |
63 and can “stab you in the back” according to |
64 this <A HREF="http://peterscott.github.io/2013/01/17/regular-expressions-will-stab-you-in-the-back/">blog post</A>. |
64 this <A HREF="http://peterscott.github.io/2013/01/17/regular-expressions-will-stab-you-in-the-back/">blog post</A>. |
65 For example, if you use in <A HREF="http://www.python.org">Python</A> or |
65 For example, if you use in <A HREF="http://www.python.org">Python</A> or |
66 in <A HREF="http://www.ruby-lang.org/en/">Ruby</A> (or also a number of other mainstream programming languages according to this |
66 in <A HREF="http://www.ruby-lang.org/en/">Ruby</A> (or also in a number of other mainstream programming languages according to this |
67 <A HREF="http://www.computerbytesman.com/redos/">blog</A>) the |
67 <A HREF="http://www.computerbytesman.com/redos/">blog</A>) the |
68 innocently looking regular expression <code>a?{28}a{28}</code> and match it, say, against the string |
68 innocently looking regular expression <code>a?{28}a{28}</code> and match it, say, against the string |
69 <code>aaaaaaaaaaaaaaaaaaaaaaaaaaaa</code> (that is 28 <code>a</code>s), you will soon notice that your CPU usage goes to 100%. In fact, |
69 <code>aaaaaaaaaaaaaaaaaaaaaaaaaaaa</code> (that is 28 <code>a</code>s), you will soon notice that your CPU usage goes to 100%. In fact, |
70 Python and Ruby need approximately 30 seconds of hard work for matching this string. You can try it for yourself: |
70 Python and Ruby need approximately 30 seconds of hard work for matching this string. You can try it for yourself: |
71 <A HREF="http://www.dcs.kcl.ac.uk/staff/urbanc/cgi-bin/repos.cgi/afl-material/raw-file/tip/progs/re.py">re.py</A> (Python version) and |
71 <A HREF="http://www.dcs.kcl.ac.uk/staff/urbanc/cgi-bin/repos.cgi/afl-material/raw-file/tip/progs/re.py">re.py</A> (Python version) and |