We revisit the analysis and design of masked cryptographic implementations to prevent side-channel attacks. Our starting point is the (known) observation that proving the security of a higher-order masked block cipher exhaustively requires unrealistic computing power. As a result, a natural strategy is to split algorithms in smaller parts (or gadgets), with as main objectives to enable both simple composition (as initiated by Barthe et al. at CCS 2016) and efficient implementations. We argue that existing composition strategies allow either trivial composition with significant overheads or optimized composition with more analysis efforts. As a result, we first introduce a new definition of Probe Isolating Non-Interference (PINI) that allows both trivial composition and efficient implementations. We next prove general composition theorems for PINI gadgets that considerably simplify the analysis of complex masked implementations. We finally design efficient multiplication gadgets that satisfy this definition. As additional results, we exhibit a limitation of existing compositional strategies for the analysis of Multiple-Inputs / Multiple-Outputs (MIMO) gadgets, extend Barthe et al. definition of Strong Non-Interference (SNI) to deal with this context, and describe an optimization method to design efficient MIMO-SNI (sub)circuits. Our results allow proving the security of a recent masked AES implementation by Goudarzi and Rivain (EUROCRYPT 2017). From the implementation viewpoint, PINI implementations reach the level of performance of the best composable masking schemes for the AES Rijndael, and outperform them by significant factors for lightweight ciphers.

中文翻译：

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轻松高效地构建带探头隔离无干扰的屏蔽小工具


我们重新审视掩码加密实现的分析和设计，以防止侧信道攻击。我们的出发点是（已知的）观察结果，证明高阶掩码分组密码的安全性完全需要不切实际的计算能力。因此，自然的策略是将算法分割成更小的部分（或小工具），其主要目标是实现简单的组合（由 Barthe 等人在 CCS 2016 上发起）和高效的实现。我们认为，现有的组合策略要么允许具有显着开销的简单组合，要么允许通过更多分析工作进行优化组合。因此，我们首先引入探针隔离无干扰 (PINI) 的新定义，它允许简单的组合和高效的实现。接下来，我们证明 PINI 小工具的一般组合定理，该定理大大简化了复杂屏蔽实现的分析。我们最终设计了满足这个定义的高效乘法小工具。作为额外的结果，我们展示了用于分析多输入/多输出（MIMO）小工具的现有组合策略的局限性，扩展 Barthe 等人。强无干扰 (SNI) 的定义来处理这种情况，并描述了一种设计高效 MIMO-SNI（子）电路的优化方法。我们的结果证明了 Goudarzi 和 Rivain 最近实施的屏蔽 AES 的安全性（EUROCRYPT 2017）。从实现的角度来看，PINI 实现达到了 AES Rijndael 的最佳可组合掩码方案的性能水平，并且在轻量级密码方面优于它们。