Semantics-based code obfuscation by abstract interpretation

Abstract

In recent years code obfuscation has attracted research interest as a promising technique for protecting secret properties of programs. The basic idea of code obfuscation is to transform programs in order to hide their sensitive information while preserving their functionality. One of the major drawbacks of code obfuscation is the lack of a rigorous theoretical framework that makes it difficult to formally analyze and certify the effectiveness of obfuscating techniques. We face this problem by providing a formal framework for code obfuscation based on abstract interpretation and program semantics. In particular, we show that what is hidden and what is preserved by an obfuscating transformation can be expressed as abstract interpretations of program semantics. Being able to specify what is masked and what is preserved by an obfuscation allows us to understand its potency, namely the amount of obscurity that the transformation adds to programs. In the proposed framework, obfuscation and attackers are modeled as approximations of program semantics and the lattice of abstract interpretations provides a formal tool for comparing obfuscations with respect to their potency. In particular, we prove that our framework provides an adequate setting to measure not only the potency of an obfuscation but also its resilience, i.e., the difficulty of undoing the obfuscation. We consider code obfuscation by opaque predicate insertion and we show how the degree of abstraction needed to disclose different opaque predicates allows us to compare their potency and resilience.

Characterizing a property-driven obfuscation strategy

“…Software watermarking is useful in identifying a violation once it has happened, while code obfuscation is considered a promising technique to prevent malicious attacks. In recent years, code obfuscation has attracted the attention of many researchers and this has led to the design and implementation of many obfuscation strategies (e.g., [7,18,33,34,40]) together with the study of theoretical models and frameworks for understanding the potentialities and limits of obfuscation (e.g., [2,4,16,21,25,39]).…”

“…This example shows us that, in order to formally reason on what is protected, namely what is concealed, and what is preserved, namely what is revealed, by an obfuscating transformation, we need to focus on the effects that obfuscation has on the program semantics. In [14,16] it is shown that the semantic level allows us to understand the protection capabilities and the limits of an obfuscating strategy with respect to a particular program. We start from the approach of Dalla Preda and Giacobazzi in [14,16] (then developed also in [20,21]), where a formal framework for code obfuscation is provided by taking into account the effects that an obfuscating transformation has on trace semantics, and by modeling attackers as approximations of trace semantics.…”

“…In [14,16] it is shown that the semantic level allows us to understand the protection capabilities and the limits of an obfuscating strategy with respect to a particular program. We start from the approach of Dalla Preda and Giacobazzi in [14,16] (then developed also in [20,21]), where a formal framework for code obfuscation is provided by taking into account the effects that an obfuscating transformation has on trace semantics, and by modeling attackers as approximations of trace semantics. In order to reason on the semantic aspects of obfuscation, we refer to the formal framework introduced by Cousot and Cousot [12], where the relation between syntactic and semantic transformations is formalized in terms of abstract interpretation by considering programs as abstractions of their semantics.…”

“…-Definition and extension of the semantic framework for code obfuscation developed in [14,16] in order to cope with the semantic specification of the properties, respectively, to protect and preserve (Sect. 3); -Definition, study and characterization of two function transformers: Revelation, which minimally (in the point-wise order) modifies a function in order to preserve a certain property of the input (Sect.…”

Using Theme-based Narrative Construct of Images as Passwords: Implementation and Assessment of Remembered Sequences

“…As suggestions to secure implementation, we used !le name and path name obfuscations to prevent hack attacks [27]. In a preliminary version of our code, the hacker could employ !le-name and !le-path to access the sequence strips and then based on a simple routine to try the permutations.…”