Still not a copyright infringement

Still not a copyright infringement

There is a largly quiet field of CS research on how to find CS students who plagarize. The researchers, for the most part, don't publicize their findings so that students can't check to see if they have obfuscated their code enough.

I did some poking around to see if I could figgure out how they work and here is what I found:

1) They typically remove all tokens (words) except the keywords. (so variable names don't matter.)
2) They often equate equivolents keywords (for and while can be used in equivolent ways)
3) They usually use an algorithm called "Running Karp Rabin" to find strings of matching tokens in two files. This algorithm is resistant to just reorderign the functions. (so it finds strings of tokens length 6 or longer which match anywhere in the file, for example)

This is likely what SCO's pattern matching team is doing, and someone on our side with access to System V should be doing it too.

I wrote a java program to test out whether this algorithm actaully finds cheaters (it did.) Feel free to e-mail me (lwn at ethanet.com) for more info/source.