Whitebox Cryptography In Software Tamper Resistance

Traditional cryptographic schemes aim to protect secret information like secret key in black-box environment,in which attackers can only access to the input and output values,along with the knowledge of the scheme.On the contrary,a cryptographic scheme is assumed to execute on an untrusted platform in white-box environment,where the adversary could have full control over internal details during the execution.Hence the traditional cryptographic schemes can no longer ensure the security of private information under white-box environment.Whitebox cryptography is designed to providing robust and secure implementations of cryptographic schemes even against white-box attacks and constructing functional cryptographic schemes with encryption,decryption and authentication abilities in white-box environment.The main technique of white-box cryptography is obfuscation: hide secret key in the obfuscated cryptographic scheme to prohibit adversary from extracting private information from the execution steps.In 2002,Chow et al.first put forward the conception of white-box environment and designed white-box DES and AES implementation,both implemented by look-up tables.All the tables are obfuscated to protect the involved secret key from exposure to the adversary.The idea of look-up tables are enlightening.Recently,several new techniques are proposed,e.g.ASASA and SPACE-HARD.White-box cryptography has attracted increasing attention and raises a significantly higher requirement towards modern cryptography system.Tamper resistance is an important issue in software protection,applied to prevent attackers from maliciously manipulation on software to fulfill illegal functionality.Typically it deals with the white-box attack model where an attacker is assumed to have full access to the software and full control over its execution,which raises crucial security problems.Code obfuscation and cryptographic hashing are common methods against the problem,incurred execution-time penalty though.Michiels et al.presented a new technique,aka.Medusa,using white-box AES implementation to make software tamper resistant in 2007.In this paper,we first introduce white-box attack context,white-box cryptography and several important white-box implementation.Then we introduce Michiels' s scheme for software tamper resistance with analysis about its pros and cons and propose two improvements.Then we propose our tamper-resistance technique,aka.Siren,with underlying white-box SMS4 implementation and give proof on its security.Siren can remedy Medusa's limitations and enlarge application range.