现实世界的快照与理论：质疑t-Probing安全模型
Real-World Snapshots vs. Theory: Questioning the t-Probing Security Model
摘要：
由于其良好的理论基础和实用效率，屏蔽已成为保护密码实现免受物理侧信道攻击（SCA）的最重要的对策。掩蔽的核心思想是在计算过程中将每个敏感中间变量随机分割为至少t+1个份额，其中t表示允许对手在不学习任何敏感信息的情况下观察到的最大份额数。换句话说，假设对手被所拥有的探测器数量（例如，微探针）或在进行高阶SCA攻击时通过统计分析的顺序（例如，差分功率分析）。这样的有界模型被用来证明相应实现的SCA安全性。因此，人们相信，只要有足够大的份额，绝大多数已知的SCA攻击都能得到缓解。在这项工作中，我们提出了一种新的激光辅助SCA技术，称为激光逻辑状态成像（LLSI），它提供了无限数量的非接触式探头，因此，违反了探测安全模型假设。这种技术使我们能够拍摄硬件实现的快照，即，在任意时钟周期，通过单次测量提取所有寄存器的逻辑状态。为了验证这一点，我们安装我们的攻击掩码AES硬件实现，并实际演示了在两种不同的情况下提取的全长密钥。首先，我们假设寄存器（键和/或状态）的位置是已知的，因此，它们的内容可以通过单个快照直接读取。其次，我们考虑一个实现与未知的寄存器位置，我们利用多个快照和SAT求解器来揭示秘密。
英文摘要：
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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