International Association
for Cryptologic Research

Software obfuscation is a powerful tool to protect the intellectual property or secret keys inside programs. Strong software obfuscation is crucial in the context of untrusted execution environments (e.g., subject to malware infection) or to face potentially malicious users trying to reverse-engineer a sensitive program. Unfortunately, the state-of-the-art of pure software-based obfuscation (including white-box cryptography) is either insecure or infeasible in practice.This work introduces OBSCURE, a versatile framework for practical and cryptographically strong software obfuscation relying on a simple stateless secure element (to be embedded, for example, in a protected hardware chip or a token). Based on the foundational result by Goyal et al. from TCC 2010, our scheme enjoys provable security guarantees, and further focuses on practical aspects, such as efficient execution of the obfuscated programs, while maintaining simplicity of the secure element. In particular, we propose a new rectangular universalization technique, which is also of independent interest. We provide an implementation of OBSCURE taking as input a program source code written in a subset of the C programming language. This ensures usability and a broad range of applications of our framework. We benchmark the obfuscation on simple software programs as well as on cryptographic primitives, hence highlighting the possible use cases of the framework as an alternative to pure software-based white-box implementations.

Cryptographic implementations deployed in real world devices often aim at (provable) security against the powerful class of side-channel attacks while keeping reasonable performances. Last year at Asiacrypt, a new formal verification tool named tightPROVE was put forward to exactly determine whether a masked implementation is secure in the well-deployed probing security model for any given security order t. Also recently, a compiler named Usuba was proposed to automatically generate bitsliced implementations of cryptographic primitives. This paper goes one step further in the security and performances achievements with a new automatic tool named Tornado. In a nutshell, from the high-level description of a cryptographic primitive, Tornado produces a functionally equivalent bitsliced masked implementation at any desired order proven secure in the probing model, but additionally in the so-called register probing model which much better fits the reality of software implementations. This framework is obtained by the integration of Usuba with tightPROVE+, which extends tightPROVE with the ability to verify the security of implementations in the register probing model and to fix them with inserting refresh gadgets at carefully chosen locations accordingly. We demonstrate Tornado on the lightweight cryptographic primitives selected to the second round of the NIST competition and which somehow claimed to be masking friendly. It advantageously displays performances of the resulting masked implementations for several masking orders and prove their security in the register probing model.