论文标题

现实世界快照与理论:质疑T-probing安全模型

Real-World Snapshots vs. Theory: Questioning the t-Probing Security Model

论文作者

Krachenfels, Thilo, Ganji, Fatemeh, Moradi, Amir, Tajik, Shahin, Seifert, Jean-Pierre

论文摘要

由于其合理的理论基础和实践效率,掩盖已成为保护加密实现免受物理侧向通道攻击(SCA)(SCAS)的最突出的对策。掩盖的核心思想是将计算过程中的每个敏感中间变量随机分配到至少t+1股中,其中t表示在不学习任何敏感信息的情况下,对手可以观察到的最大股票数量。换句话说,假定对手在进行高阶SCA攻击时(例如,差异功率分析)时,具有拥有数量的探针(例如,微探针)或统计分析的顺序界定。使用这种有限的模型来证明相应实现的SCA安全性。因此,据信,鉴于大量股份,绝大多数已知的SCA攻击都得到了减轻。在这项工作中,我们提出了一种新颖的激光辅助SCA技术,称为激光逻辑状态成像(LLSI),该技术提供了无限数量的非接触式探针,因此违反了探测安全模型假设。这项技术使我们能够对硬件实现进行快照,即,在任何任意时钟周期中提取所有寄存器的逻辑状态,并进行单个测量。为了验证这一点,我们对蒙面的AES硬件实现进行了攻击,并实际上证明了在两种不同的情况下提取全长密钥的提取。首先,我们假设已知寄存器的位置(键和/或状态),因此,可以通过一个快照直接读取它们的内容。其次,我们考虑一个具有未知寄存器位置的实现,我们利用多个快照和一个SAT求解器来揭示秘密。

Due to its sound theoretical basis and practical efficiency, masking has become the most prominent countermeasure to protect cryptographic implementations against physical side-channel attacks (SCAs). The core idea of masking is to randomly split every sensitive intermediate variable during computation into at least t+1 shares, where t denotes the maximum number of shares that are allowed to be observed by an adversary without learning any sensitive information. In other words, it is assumed that the adversary is bounded either by the possessed number of probes (e.g., microprobe needles) or by the order of statistical analyses while conducting higher-order SCA attacks (e.g., differential power analysis). Such bounded models are employed to prove the SCA security of the corresponding implementations. Consequently, it is believed that given a sufficiently large number of shares, the vast majority of known SCA attacks are mitigated. In this work, we present a novel laser-assisted SCA technique, called Laser Logic State Imaging (LLSI), which offers an unlimited number of contactless probes, and therefore, violates the probing security model assumption. This technique enables us to take snapshots of hardware implementations, i.e., extract the logical state of all registers at any arbitrary clock cycle with a single measurement. To validate this, we mount our attack on masked AES hardware implementations and practically demonstrate the extraction of the full-length key in two different scenarios. First, we assume that the location of the registers (key and/or state) is known, and hence, their content can be directly read by a single snapshot. Second, we consider an implementation with unknown register locations, where we make use of multiple snapshots and a SAT solver to reveal the secrets.

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