The use of computers, electronic computing devices and computer software in all of their various forms is recognized to be very common and is growing every day. As well, with the pervasiveness of powerful communication networks, the ease with which computer software programs and data files may be accessed, exchanged, copied and distributed is also growing daily. In order to take advantage of these computer and communication systems and the efficiencies that they offer, there is a need for a method of storing and exchanging computer software and data securely.
One method of maintaining confidentiality or privacy that has demonstrated widespread use and acceptance is encryption of data using secret cryptographic keys. Existing encryption systems are designed to protect their secret keys or other secret data against a “black box attack”. This is a situation where an attacker has knowledge of the algorithm and may examine various inputs to and outputs from the algorithm, but has no visibility into the execution of the algorithm itself (such as an adaptive chosen input/output attack).
While cryptographic systems relying on the black box model are very common, it has been shown that this model does not reflect reality. Often, the attacker is in a position to observe at least some aspect of the execution of the algorithm, and has sufficient access to the targeted algorithm to mount a successful attack (i.e. side-channel attacks such as timing analysis, power analysis, cache attacks, fault injection, etc.) Such attacks are often referred to as “grey-box” attacks, the assumption being that the attacker is able to observe at least part of the system execution.
Recognizing this, an effort has been made to design encryption algorithms and data channels which are resistant to a more powerful attack model—the “white box attack”. A white box attack is an attack on a software algorithm in which it is assumed that the attacker has full visibility into the execution of the algorithm. To date, such protection systems have met with reasonable success, but as such protection systems have become more and more sophisticated, so has the sophistication of the attacking techniques (such as encoding reduction attacks, statistical bucketing attacks and homomorphic mapping attacks). Thus, many existing white box protection systems are being shown to be ineffective against concerted attacks.
Obfuscation of software by means of simple encodings has been in use for some time. In order to be useful, applications of such encodings in software obfuscation must not increase the time and space consumption of the software unduly, so such encodings are typically relatively simple. Hence, while they can protect software in bulk, they do not provide a high degree of security. There are many communication boundaries in software which represent particular vulnerabilities: passage of data in unprotected form into or out of an obfuscated program, passage of data into or out of a cipher implementation in software or hardware, and the like. The strength of prior encoding strategies typically is sharply limited by the data sizes which they protect. For conventional encodings, such protected items are on the order of 32 bits, sometimes 64 bits, and sometimes smaller pieces of data such as characters or bytes. Given the limitations of encodings and the operand sizes, fairly swift brute-force cracking of such encodings cannot be prevented in general.
There is therefore a need for more effective secret-hiding and tamper-resistance techniques, providing protection of software code and data in general, as well as protection of secret cryptographic keys, biometric data, encrypted data and the like. It also is desirable to provide a much stronger form of protection for software boundaries than conventional simple encodings.