IEEE Spectrum October, 2010 - 48

Software v. Software

age, rather than unique features, such as the number of tail fins.
And rather than rendering a definitive verdict that illegal copying has or hasn't occurred, CodeMatch relies on measurable
Continued from page 35
quantities that can be used to judge the likelihood of copying.
CodeMatch works by gauging the statistical correlation of
just the threat of a plagiarism-detection program, whether it
two variables. A correlation of 0 indicates that the two variaworked or not, was enough to discourage cheating.
The goals of a software forensics tool used in intellectual- bles are unrelated. A correlation of 1 indicates that a change in
property litigation have to be very different. In these cases, there one variable always causes a similar change in the other. And
may be hundreds of millions of dollars at stake. The tool must -1 indicates a completely opposite correspondence between
favor false positives over false negatives so that it does not miss their variations. For source-code fi les that have no similariany cases of copying; an expert can then examine the results and ties, the correlation is 0; for identical files, it's 1.
eliminate those false positives. And it must be
fast, but not at the expense of accuracy; in these
high-stakes cases, it's fine to dedicate a computer or set of computers to analyze the code
for a day, a week, or even a month if necessary.

>
>
>
>

few people have the expertise to parse
source code--the human-readable form
of a program--to determine what, if
anything, has been illegally reproduced

o how do you go about creating such a
software forensics tool? I spent about
a year developing CodeMatch, for use
in copyright infringement cases. My company released
the first version in 2003, and the program has been
evolving ever since. Here are the basic principles I followed in
developing CodeMatch. First, the tool can analyze source code in
a way that's independent of the programming language. That's
extremely important, given the wide variety of software cases
in which the program is used. To be able to do that, CodeMatch
focuses on characteristics in the code that are generic to all
types of source code. If the program were comparing automobile
designs instead, it might look at characteristics such as gas mile-

CodeMatch looks for such correlations by examining and
comparing two collections of source-code fi les. Source code
consists of statements, which include the instructions and
identifiers that guide the program, as well as comments and
strings that serve to document the code but cause no action
to occur. A single line of source code may include one or more
statements and one or more comments.
CodeMatch spots correlations in four places: statements,
comments/strings, identifiers, and instruction sequences.
Each type of correlation offers a clue to plagiarism that the

The Exact Lens you need,
The Expert Support you want
Universe Kogaku America designs
Lens Assemblies for Every Application...

Custom Lens Designer and Manufacturer.
Thousands of Lens Sizes in Stock.
Most Lenses Ship Same Day.

Medical Imaging Lenses
Microscope Objectives & Eyepieces
Photographic Lenses
Lens Mounting Accessories
Lens Filters and Accessories
Image and Barcode Lenses
UV Quartz Lenses
CCD and CMOS Lenses
CCTV Lenses
Diode Laser Lenses
High Resolution Lenses
Your Custom Lens Assembly

Focus on Medical Lenses

from Prototype to Production
Lens assemblies for medical imaging and diagnostic cameras
from Universe Kogaku are available off-the-shelf in a wide
variety of sizes and styles designed for use with today's highresolution diagnostic cameras. Our design capability and 60
years of manufacturing experience allow us to produce any
special lens.... in any quantity! Applications include Endoscope
and fiber scope couplers, diagnostic camera hand pieces, and
medical X-ray scanning. Contact Universe for drawings, full
performance data, and pricing.

www.UKAoptics.com
In USA: 516-624-2444
48

Na * iEEE SpEctrum * octobEr 2010

Email: info@ukaoptics.com

spectrum.ieee.org

http://www.UKAoptics.com http://spectrum.ieee.org

Table of Contents for the Digital Edition of IEEE Spectrum October, 2010