Algorithmic Information Theory for Obfuscation Security

Proceedings of the forty-sixth annual ACM symposium on Theory of computing, 2014

We introduce a new technique, that we call punctured programs, to apply indistinguishability obfuscation towards cryptographic problems. We use this technique to carry out a systematic study of the applicability of indistinguishability obfuscation to a variety of cryptographic goals. Along the way, we resolve the 16-year-old open question of Deniable Encryption, posed by Canetti, Dwork, Naor, and Ostrovsky in 1997: In deniable encryption, a sender who is forced to reveal to an adversary both her message and the randomness she used for encrypting it should be able to convincingly provide "fake" randomness that can explain any alternative message that she would like to pretend that she sent. We resolve this question by giving the first construction of deniable encryption that does not require any pre-planning by the party that must later issue a denial. In addition, we show the generality of our punctured programs technique by also constructing a variety of core cryptographic objects from indistinguishability obfuscation and one-way functions (or close variants). In particular we obtain: public key encryption, short "hash-and-sign" selec-

IACR Cryptol. ePrint Arch., 2015

We introduce a new, instance-based notion of indistinguishability obfuscation, called computation-trace indistinguishability obfuscation (CiO), for (parallel) RAM computation. CiO only obfuscates a fixed, single computation instance, as opposed to iO which obfuscates a function on all input instances. Specifically, for Π defined by (P, x) consisting of a (parallel) RAM program P and an input x, the obfuscations of two instances Π and Π′ are required to be indistinguishable only when the execution of Π and Π′ generate an identical computation trace; namely, identical sequences of CPU states and memory content. On the other hand, we require the obfuscation to be (i) fully succinct: the runtime of the obfuscator (and thus the size of the obfuscated instance) depends only on the description and input/output size of Π, but is independent of the time and space complexities of Π, and (ii) efficiency preserving: the obfuscated instance is a (parallel) RAM program that preserves parallel/tot...

Proceedings of the 2007 ACM workshop on Quality of protection - QoP '07, 2007

Despite the recent advances in the theory underlying obfuscation, there still is a need to evaluate the quality of practical obfuscating transformations more quickly and easily. This paper presents the first steps toward a comprehensive evaluation suite consisting of a number of deobfuscating transformations and complexity metrics that can be readily applied on existing and future transformations in the domain of binary obfuscation. In particular, a framework based on software complexity metrics measuring four program properties: code, control flow, data and data flow is suggested. A number of well-known obfuscating and deobfuscating transformations are evaluated based upon their impact on a set of complexity metrics. This enables us to quantitatively evaluate the potency of the (de)obfuscating transformations.

IACR Cryptol. ePrint Arch., 2019

Relative cryptographic semantic security for encrypted words of user data at runtime holds in the emerging field of encrypted computing, in conjunction with an appropriate instruction set and compiler. An information obfuscation calculus for program compilation in that context is introduced here that quantifies the security exactly, improving markedly on the result.

Context: code obfuscation is intended to obstruct code understanding and, eventually, to delay malicious code changes and ultimately render it uneconomical. Although code understanding cannot be completely impeded, code obfuscation makes it more laborious and troublesome, so as to discourage or retard code tampering. Despite the extensive adoption of obfuscation, its assessment has been addressed indirectly either by using internal metrics or taking the point of view of code analysis, e.g., considering the associated computational complexity. To the best of our knowledge, there is no publicly available user study that measures the cost of understanding obfuscated code from the point of view of a human attacker. Aim: this paper experimentally assesses the impact of code obfuscation on the capability of human subjects to understand and change source code. In particular, it considers code protected with two well-known code obfuscation techniques, i.e., identifier renaming and opaque predicates. Method: We have conducted a family of five controlled experiments, involving undergraduate and graduate students from four Universities. During the experiments, subjects had to perform comprehension or attack tasks on decompiled clients of two Java network-based ap-2 plications, either obfuscated using one of the two technique, or not. To assess and compare the obfuscation techniques, we measured the correctness and the efficiency of the performed task.

Communications in Computer and Information Science

In the realm of protecting programs from illegitimate use, obfuscation offers a modicum of defense against malicious reverse engineering and tampering. As a field of study, obfuscation would benefit from a unifying framework that has solid theoretical foundation yet provides value in empirical study and implementation. The essence of obfuscation (in practice) is best described as a measurable loss of abstraction. We argue that mathematical frameworks such as abstract interpretation and Boolean algebras may provide an ideal marriage of theory and practice, providing focused direction for future research.

Lecture Notes in Computer Science, 2009

Existing definitions of program obfuscation do not rule out malleability attacks, where an adversary that sees an obfuscated program is able to generate another (potentially obfuscated) program that is related to the original one in some way.

2020 IEEE International Workshop on Information Forensics and Security (WIFS), 2020

We consider the problem of privacy-preserving data release for a specific utility task under perfect obfuscation constraint. We establish the necessary and sufficient condition to extract features of the original data that carry as much information about a utility attribute as possible, while not revealing any information about the sensitive attribute. This problem formulation generalizes both the information bottleneck and privacy funnel problems. We adopt a local information geometry analysis that provides useful insight into information coupling and trajectory construction of spherical perturbation of probability mass functions. This analysis allows us to construct the modal decomposition of the joint distributions, divergence transfer matrices, and mutual information. By decomposing the mutual information into orthogonal modes, we obtain the locally sufficient statistics for inferences about the utility attribute, while satisfying perfect obfuscation constraint. Furthermore, we develop the notion of perfect obfuscation based on χ 2-divergence and Kullback-Leibler divergence in the Euclidean information space.

Proceedings of the …, 2008

2017 IEEE 58th Annual Symposium on Foundations of Computer Science (FOCS), 2017

In this paper we introduce the notion of lockable obfuscation. In a lockable obfuscation scheme there exists an obfuscation algorithm Obf that takes as input a security parameter λ, a program P , a message msg and "lock value" α and outputs an obfuscated program P . One can evaluate the obfuscated program P on any input x where the output of evaluation is the message msg if P (x) = α and otherwise receives a rejecting symbol ⊥. We proceed to provide a construction of lockable obfuscation and prove it secure under the Learning with Errors (LWE) assumption. Notably, our proof only requires LWE with polynomial hardness and does not require complexity leveraging. We follow this by describing multiple applications of lockable obfuscation. First, we show how to transform any attribute-based encryption (ABE) scheme into one in which the attributes used to encrypt the message are hidden from any user that is not authorized to decrypt the message. (Such a system is also know as predicate encryption with one-sided security.) The only previous construction due to Gorbunov, Vaikuntanathan and Wee is based off of a specific ABE scheme of Boneh et al. By enabling the transformation of any ABE scheme we can inherent different forms and features of the underlying scheme such as: multi-authority, adaptive security from polynomial hardness, regular language policies, etc. We also show applications of lockable obfuscation to separation and uninstantiability results. We first show how to create new separation results in circular encryption that were previously based on indistinguishability obfuscation. This results in new separation results from learning with error including a public key bit encryption scheme that it IND-CPA secure and not circular secure. The tool of lockable obfuscation allows these constructions to be almost immediately realized by translation from previous indistinguishability obfuscation based constructions. In a similar vein we provide random oracle uninstantiability results of the Fujisaki-Okamoto transformation (and related transformations) from the lockable obfuscation combined with fully homomorphic encryption. Again, we take advantage that previous work used indistinguishability obfuscation that obfuscated programs in a form that could easily be translated to lockable obfuscation.