Design And Security Analysis In White-Box Cryptography

Recently,people began to pay more and more attentions to Software Protection. It is referred as White-Box Cryptography when the issue concerns about the cipher algorithm protection in Software Protection area. Different from traditional cryptographic attack environment, in WBAC(White-Box Attack Context), the most important information——the key, is not protected while running the program. The attacker can obtain information of key by simply observing the process of software running. The White-Box Cryptography is just the solution for this kind of issue.The main focuses nowadays are design of White-Box Algorithm and theoretical foundation of White-Box Cryptography. In the algorithm aspect, there are two ways to construct a White-Box cipher: Chow provided the idea using look-up tables to implement White-Box cipher. By hiding key information in look-up tables, attackers can no longer access to the key. Bringer gave another attempt by adding perturbation to original algorithm in order to prevent attacker to analysis the algebra structure. However, there two attempts are all failed.In this paper, we first introduce White-Box Context and White-Box Cryptography. And the instances of Chow White-Box AES, using look-up tables, and Bringer White-Box AEw/oS, using Zero Polynomial to add perturbation are also presented.Then, we provide an improvement of White-Box AES implementation, through analysis of advantages and disadvantages of both above algorithm. Our implement increases the analysis difficulties to attacker by adding perturbation to original Chow's White-Box AES implement and modifying the MixColumns matrix.At last, we propose a concept of Obfuscation Degree after summarization and analysis of recent White-Box attack. This Obfuscation Degree is a measurement of White-Box implement.