Protecting the NOEKEON Cipher against SCARE Attacks in FPGAs by Using Dynamic Implementations

Abstract

Protecting an implementation against Side Channel Analysis for Reverse Engineering (SCARE) attacks is a great challenge and we address this challenge by presenting a first proof of concept. White-box cryptography has been developed to protect programs against an adversary who has full access to their software implementation. It has also been suggested as a countermeasure against side channel attacks and we examine here these techniques in the wider perspective of SCARE. We consider that the adversary has only access to the cryptographic device through its side channels and his goal is to recover the specifications of the algorithm. In this work, we focus on FPGA (Field-Programmable Gate Array) technologies and examine how to thwart SCARE attacks by implementing a block cipher following white-box techniques. The proposed principle is based on changing dynamically the implementations. It is illustrated by an example on the Noekeon cipher and feasibility in different FPGAs is studied.

Evaluation of White-Box and Grey-Box Noekeon Implementations in FPGA

“…A first hardware grey-box implementation was proposed for the Noekeon cryptographic algorithm in [7]. Whereas in the case of white-box implementations the encoding functions were static, the grey-box implementation uses dynamic encoding functions.…”

“…1-bit dynamic encoding functions benefit from the 1-bit static encoding functions' advantages while removing their drawbacks. In the implementation proposed by J. Bringer et al [7], two random bits are added to each LUT. One of these bits is used to randomly select one decoding input function between two bijections, the other random bit selects one encoding output function between two other bijections.…”

“…The grey-box Noekeon implementation presented in [7] includes a mixing bijection before the linear application, as introduced by Chow et al [2]. However, since the dynamic encoding functions are sufficient to protect the Noekeon implementation against SCA, we could remove the mixing bijection from our design without reducing the circuit's robustness.…”

“…Software white-box implementations for DES and AES have been proposed in [1], [2], while several cryptanalytic works have been done on such implementations [3]- [6]. Then, a hardware grey-box implementation has been introduced in [7] to thwart Side Channel Attacks against Reverse Engineering (SCARE) [8]. The grey-box approach is a degradation of the white-box approach, where some variables are random, hence reputed unknown.…”

“…In this work we focus on key recovery. We will therefore experimentally evaluate the greybox hardware implementation of the Noekeon cipher that has been proposed by J. Bringer et al in [7] and we will propose a white-box alternative using 3-bits encoding functions.…”