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    计数器溢出可感知的非易失性存储器安全重加密延迟优化技术

    Counter Overflow-Aware Optimization Technique for Secure Delayed Re-Encryption in Non-Volatile Memory

    • 摘要: 非易失性存储器(non-volatile memory,NVM)因断电后数据持久保存、高密度和大容量等优势成为了研究热点,但其持久性也使其更易遭受未授权访问与数据篡改等安全威胁。安全NVM通常采用加密与完整性验证技术,但直接加密会引发写放大,导致写入延迟增加和能耗上升。为缓解该问题,提出计数器溢出可感知的安全重加密延迟优化技术(epoch-based re-encryption delay,ERED),包括基于周期的字级重加密延迟优化技术(word-epoch based re-encryption delay,W-ERED)与基于周期的行级重加密延迟优化技术(line-epoch based re-encryption delay,L-ERED)。W-ERED通过为局部计数器设置溢出标志,在溢出时仅对溢出数据字使用新的行计数器加密,未溢出数据字仍使用旧行计数器,从而避免不必要的重加密。在此基础上,L-ERED通过为行计数器设置溢出标志,在溢出发生时仅对溢出数据行使用主计数器重加密,显著减小因行计数器溢出导致的重加密粒度。进一步提出STAR+以优化写入开销并增强崩溃恢复能力:引入计数器写过滤机制,仅当缓存中计数器更新达到阈值时写入NVM;恢复阶段结合Osiris与影子计数器重建计数器状态,并通过更新MAC与递归计算哈希恢复完整性树,确保数据与元数据一致性。实验结果表明,与智能加密节能技术(smartly encrypted energy efficient,SECRET)相比,W-ERED平均位翻转率降低5%、写入延迟降低11%、写入能耗降低6%,存储开销仅增加8/512;L-ERED重加密行数仅为BASE方案的26.7%和RSR方案的47.7%,额外存储开销为1/512;STAR+较STAR写入次数减少9.8%、性能开销降低3.1%,恢复时间基本持平。

       

      Abstract: Non-volatile memory (NVM), with the advantages of persistence after power failure, high density, and large capacity, has attracted extensive attention from both academia and industry. However, its persistence also makes NVM more vulnerable to security threats such as unauthorized access and data tampering. To ensure data confidentiality and integrity during storage and access, secure NVM systems generally employ encryption and integrity verification mechanisms. Nevertheless, directly applying these mechanisms to NVM may cause severe write amplification, resulting in increased write latency and energy consumption. To address this problem, this paper proposes epoch-based re-encryption delay (ERED), including word-epoch-based re-encryption delay (W-ERED) and line-epoch-based re-encryption delay (L-ERED). Since the re-encryption frequency of a data line is usually dominated by its most frequently updated word, W-ERED introduces flag bits for local counters to identify frequently overflowing words. When a local counter overflows, only the overflowing word is re-encrypted with a new line counter, while non-overflowing words continue to use the old line counter, thereby avoiding unnecessary re-encryption operations. Based on this observation, L-ERED further exploits the fact that the re-encryption rate of a data page is mainly determined by the data line with the highest overflow frequency in that page. By introducing overflow flags for line counters, L-ERED ensures that only overflowing data lines are re-encrypted with the major counter upon overflow, thus significantly reducing the re-encryption granularity and overhead caused by line-counter overflow. Furthermore, to reduce write overhead and improve crash recovery capability, this paper proposes an enhanced scheme, STAR+. STAR+ introduces a counter write-filtering mechanism that writes counters back to NVM only when the number of cache updates reaches a preset threshold, thereby reducing counter write operations. During crash recovery, STAR+ adopts the Osiris technique and uses shadow counters to record incremental updates. It reconstructs counter states by reading persisted counter values, replaying the logged increments, and verifying their correctness. In addition, STAR+ restores the integrity tree by updating the authentication values of leaf and parent nodes and recursively recalculating upper-level hash values, thereby ensuring consistency between data and metadata. Experimental results show that, compared with SECRET, W-ERED reduces the average write bit-flip rate by 5%, write latency by 11%, and write energy by 6%, with only 8/512 additional storage overhead. In L-ERED, the number of re-encrypted lines is only 26.7% of that in BASE and 47.7% of that in RSR, with only 1/512 additional storage overhead. Moreover, compared with STAR, STAR+ reduces NVM writes by 9.8% and performance overhead by 3.1%, while achieving comparable recovery time.

       

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