关键词: 条件代码加密, 路径分支混淆, 拉格朗日插值法, 多输入分支, 代码保护

Abstract: Code encryption based on path branch obfuscation of equal condition can make the key be apart from the encrypted program, so this encryption can oppose static and dynamic programming analysis method at the same time, but it can’t be used with branches controlled by other comparative relationships. In this paper, using Lagrange interpolation method to produce input-preprocess function, we not only resolve the uniqueness problem of key which produced by multi-inputs of the branch, but also preserve the security of obfuscation on branch conditions, so the conditional code of multi-inputs branch can be encrypted. Using the method which resolves the uniqueness problem of key, code encryption based on equal condition branch obfuscation can be extended to branch of greater-than and less-than condition branch, and complicate condition branch formed by blending of interval condition and equal condition.

Key words: conditional code encryption, path branch obfuscation, Lagrange interpolation method, multi-input branch, code protection