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-<b>MSc Projects</b>
-
-<p>
-start of paragraph. <cyan> a <red>cyan</red> word</cyan> normal again something longer.
-</p>
-
-
- <p><b>Description:</b>
- <a>Regular expressions</a> are extremely useful for many text-processing tasks such as finding patterns in texts,
- lexing programs, syntax highlighting and so on. Given that regular expressions were
- introduced in 1950 by <a>Stephen Kleene</a>, you might think
- regular expressions have since been studied and implemented to death. But you would definitely be mistaken: in fact they are still
- an active research area. For example
- <a>this paper</a>
- about regular expression matching and partial derivatives was presented this summer at the international
- PPDP'12 conference. The task in this project is to implement the results from this paper.</p>
-
- <p>The background for this project is that some regular expressions are
- <a>evil</a>
- and can stab you in the back; according to
- this <a>blog post</a>.
- For example, if you use in <a>Python</a> or
- in <a>Ruby</a> (probably also in other mainstream programming languages) the
- innocently looking regular expression a?{28}a{28} and match it, say, against the string
- <red>aaaaaaaaaaaaaaaaaaaaaaaaaaaa</red> (that is 28 as), you will soon notice that your CPU usage goes to 100%. In fact,
- Python and Ruby need approximately 30 seconds of hard work for matching this string. You can try it for yourself:
- <a>re.py</a> (Python version) and
- <a>re.rb</a>
- (Ruby version). You can imagine an attacker
- mounting a nice <a>DoS attack</a> against
- your program if it contains such an evil regular expression. Actually
- <a>Scala</a> (and also Java) are almost immune from such
- attacks as they can deal with strings of up to 4,300 as in less than a second. But if you scale
- the regular expression and string further to, say, 4,600 as, then you get a
- StackOverflowError
- potentially crashing your program.
- </p>