AB-ORAM: Constructing Adjustable Buckets for Space Reduction in Ring ORAM
AB-ORAM: Constructing Adjustable Buckets for Space Reduction in Ring ORAM
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DOI：
10.1109/hpca56546.2023.10071064
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发表时间：
2023-02
期刊：
影响因子：
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通讯作者：
Mehrnoosh Raoufi;Jun Yang;Xulong Tang;Youtao Zhang
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文献类型：
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作者：
Mehrnoosh Raoufi;Jun Yang;Xulong Tang;Youtao Zhang
环ORAM(不经意RAM)是一种安全原语，它通过减少在线内存带宽需求，即服务于实际内存请求的内存访问次数来缓解ORAM的巨大性能降级。Ring Oram需要4倍或更多的受保护数据空间来实现优化，因此给现代存储系统带来了高容量压力。虽然最近的研究致力于通过桶压实来降低其空间消耗，但巨大的空间消耗仍然是Ring Oram的一大设计挑战。AB-Oram发现了Ring Oram中存储空间的两种低效使用：(I)被访问的块保存无用数据，直到下一次重新洗牌操作；以及(Ii)大的存储桶为靠近树叶的树级提供了递减的性能优势。然后，AB-Oram分别提出了两种利用优化机会的方案。具体地说，它通过将访问的块分配到需要重新洗牌的存储桶来提早回收；并缩小树级接近树叶的存储桶大小，以实现更好的空间/性能权衡。我们评估了建议的AB-Oram设计，并将其与最先进的设计进行了比较。我们的结果表明，AB-Oram在引入非常低的性能开销的同时，比最先进的技术平均减少了36%的空间。
Ring ORAM (Oblivious RAM) is a secure primitive that mitigates the large performance degradation of ORAM through reduced online memory bandwidth demand, i.e., the number of memory accesses at servicing a real memory request. Ring ORAM requires 4× or more of the protected data space to enable the optimization and thus presents high capacity pressure on modern memory systems. While recent studies strive to reduce its space consumption through bucket compaction, the large space consumption remains a major design challenge for Ring ORAM.In this paper, we propose AB-ORAM to reduce the space capacity demand in Ring ORAM. AB-ORAM identifies two inefficient use of memory space in Ring ORAM: (i) accessed blocks hold useless data until the next reshuffle operation; and (ii) large buckets provide a diminishing performance benefit for tree levels close to the leaves. AB-ORAM then proposes two schemes to exploit the optimization opportunities, respectively. Specifically, it reclaims accessed blocks early by allocating them to buckets that need a reshuffle; and shrinks the bucket size for tree level close to the leaves for a better space/performance trade-off. We evaluate the proposed AB-ORAM design and compare it to the state-of-the-art. Our results show that AB-ORAM achieves an average of 36% space reduction over the state-of-the-art while introducing very low performance overhead.