THE game may be up for people who cheat in 鈥渄istributed computing鈥� projects,
in which computer owners donate or sell their surplus computer time. Projects
like this include the Search for Extraterrestrial Intelligence (SETI), where
participants use their PCs to hunt for intelligent radio transmissions from
outer space.
SETI was the first large-scale distributed-computing project, and it relies
solely on volunteers. But in the past few years, companies have been racing to
capitalise on the idea, paying participants in proportion to the computer
downtime they donate. Instead of searching for ET, these companies tackle giant
number-crunching problems such as identifying genes or cancer-blocking
molecules, or cracking codes.
And whenever money is on offer it鈥檚 only a matter of time before some clever
hacker figures out how to make it look as if their computer did calculations
that it did not鈥攁llowing them to earn cash while they play computer games
or surf the Net.
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But now Philippe Golle and Ilya Mironov, both graduate students in computer
science at Stanford University, have developed a way to detect cheats. They
insert a few fake 鈥渉its鈥� into each data set sent out to be crunched. If a
participant returns the data without finding the planted hits, the company knows
the data was not searched.
Suppose a company was hired to uncover a secret key used to encrypt a
plain-text message. Each participant鈥檚 computer must analyse thousands of
possible keys. Cheats could claim to have tried all their keys, but since they
don鈥檛 know how many fake correct keys are hidden in their data, they must try
all of them to earn their fee.
Even when no payment is involved, as with SETI, some people cheat to be
listed as a top performer on the project鈥檚 website. With 2.7 million members,
SETI sends each data set to multiple participants, thus ensuring all the data is
thoroughly searched. But for companies without that luxury, the Stanford scheme
could be useful, says David Anderson, director of SETI@home and chief technical
officer of United Devices, a commercial distributed-computing company.