As various computers are connected into a world wide network, software is a
target of copyright pirates, attackers, or even terrorists, as a result,
software protections become a more and more important issue for software users
and developers. There are some technical measures for software protections, such
as hardware-based protections and software-based techniques [1], etc. Software
obfuscation [2] is one of these measures to protect software from unauthorized
modification by making software more obscure so that it is hard for potential
attackers to understand the obfuscated software. There are several algorithms of
software obfuscation such as layout transformation, computation transformation,
ordering transformation, and data transformation [2]. Variable transformation is
a major method of data transformation to transform software into a new
semantically equivalent one that is hard for attackers to understand the true
meaning of variables in software.