PEARL: Plausibly Deniable Flash Translation Layer using WOM coding
PEARL: Plausibly Deniable Flash Translation Layer using WOM coding
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发表时间：
2020-09
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通讯作者：
Chen Chen-Chen;Anrin Chakraborti;R. Sion
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作者：
Chen Chen-Chen;Anrin Chakraborti;R. Sion
当对手强大到足以迫使用户透露加密密钥时，仅加密就不足以保护数据。合理否认（PD）机制通过使用户能够隐藏敏感数据的存在来解决这个问题，通常通过提供托管在同一设备上的看似合理的“封面文本”或“公共数据卷”。不幸的是，随着（NAND）闪存作为高性能、经济高效的存储介质的日益普及，PD在现实对手的存在下变得更具挑战性，这些对手通常可以在多个时间点访问设备（“多快照”）。这是因为对闪存的读/写操作不会导致对底层设备状态的直观的对应改变。这种行为大多是专有的，这一事实使问题进一步复杂化。例如，在大多数市售闪存设备中，从上层发出的删除或重写操作几乎肯定不会导致底层闪存单元的实际立即擦除。为了解决这些挑战，我们设计了一类新的一次写入存储器（WOM）代码，将隐藏位存储在与其他公共位相同的物理位置。这是通过NAND闪存的固有性质以及向先前未在现有页中写入的目标单元发出多次写入的可能性而实现的。我们设计了PEARL，这是一个通用的闪存转换层（FTL），允许用户在NAND闪存设备中存储隐藏数据。我们在广泛使用的模拟器FlashSim上实现并评估了PEARL（Kim等人，2019）。PEARL在真实世界的工作负载上表现良好，与非PD基线一致。PEARL是第一个为NAND闪存设备实现强大的合理可否认性的系统，可以抵御真实的多快照对手。
When adversaries are powerful enough to coerce users to reveal encryption keys, encryption alone becomes insufficient for data protection. Plausible deniability (PD) mechanisms resolve this by enabling users to hide the mere existence of sensitive data, often by providing plausible "cover texts" or "public data volumes" hosted on the same device. Unfortunately, with the increasing prevalence of (NAND) flash as a high-performance cost-effective storage medium, PD becomes even more challenging in the presence of realistic adversaries who can usually access a device at multiple points in time ("multi-snapshot"). This is because read/write operations to flash do not result in intuitive corresponding changes to the underlying device state. The problem is further compounded by the fact that this behavior is mostly proprietary. For example, in a majority of commercially-available flash devices, an issued delete or overwrite operation from the upper layers almost certainly won't result in an actual immediate erase of the underlying flash cells. To address these challenges, we designed a new class of write-once memory (WOM) codes to store hidden bits in the same physical locations as other public bits. This is made possible by the inherent nature of NAND flash and the possibility of issuing multiple writes to target cells that have not previous been written to in existing pages. We designed PEARL, a general-purpose Flash Translation Layer (FTL) that allows users to plausibly deniably store hidden data in NAND flash devices. We implemented and evaluated PEARL on a widely used simulator FlashSim (Kim et al. 2019). PEARL performs well on real-world workloads, comparably to non-PD baselines. PEARL is the first system that achieves strong plausible deniability for NAND flash devices, secure against realistic multi-snapshot adversaries.