Untrusted Providers Research Articles

FileDAG: A Multi-Version Decentralized Storage Network Built on DAG-Based Blockchain

Decentralized Storage Networks (DSNs) can gather storage resources from mutually untrusted providers and form worldwide decentralized file systems. Compared to traditional storage networks, DSNs are built on top of blockchains, which can incentivize service providers and ensure strong security. However, existing DSNs face two major challenges. First, deduplication can only be achieved at the directory-level. Missing file-level deduplication leads to unavoidable extra storage and bandwidth cost. Second, current DSNs realize file indexing by storing extra metadata while blockchain ledgers are not fully exploited. To overcome these problems, we propose FileDAG, a DSN built on DAG-based blockchain to support file-level deduplication in storing multi-versioned files. When updating files, we adopt an increment generation method to calculate and store only the increments instead of the entire updated files. Besides, we introduce a two-layer DAG-based blockchain ledger, by which FileDAG can provide flexible and storage-saving file indexing by directly using the blockchain database without incurring extra storage overhead. We implement FileDAG and evaluate its performance with extensive experiments. The results demonstrate that FileDAG outperforms the state-of-the-art industrial DSNs considering storage cost and latency.

Verifying multiple replica possession with public key segment under public cloud storage environment

AbstractReplication is widely used in cloud storage systems to provide availability and reliability for outsourced cloud data. However, untrusted providers would like to maintain fewer replicas than promise for economic profits or other benefits. Since providers hardly ever offer remote checking tools, it becomes a challenge to validate from user side whether Providers are faithfully keeping enough replicas or not. Existing solutions have several disadvantages, including low efficiency, high computation overload, and lack of supporting for colluding attack. In this article, a collector‐based multiple replica storage model is introduced. Based on that, a novel multiple replica possession proving scheme public key segment is proposed in detail. Particularly, a public key is divided into several private segments, which will be distributed to corresponding storage servers for evidence generation. Only if every replica node shows its correct possession evidence, can the challenge be concluded as success. Theoretical analysis and prototype experiments show the correctness, security, and efficiency of the scheme.

ConcurDB: Concurrent Query Authentication for Outsourced Databases

Clients of outsourced databases need Query Authentication (QA) guaranteeing the integrity and authenticity of query results returned by potentially compromised providers. Prior work provides QA assurances for a limited class of queries by deploying several software-based cryptographic constructs. The constructs are often designed assuming read-only or infrequently updated databases. For dynamic datasets, the data owner is required to perform all updates on behalf of clients. Hence, for concurrent updates by multiple clients, such as for OLTP workloads, existing QA solutions are inefficient. We present ConcurDB, a concurrent QA scheme that enables simultaneous updates by multiple clients. To realize concurrent QA, we have designed several new mechanisms. First, we identify and use an important relationship between QA and memory checking to decouple query execution and verification. We allow clients to execute transactions concurrently and perform verifications in parallel using an offline memory checking based protocol. Then, to extend QA to a multi-client scenario, we design new protocols that enable clients to securely exchange a small set of authentication data even when using the untrusted provider as a communication hub. Finally, we overcome provider-side replay attacks. Using ConcurDB, we provide and evaluate concurrent QA for the full TPC-C benchmark. For updates, ConcurDB shows a 4x performance increase over existing solutions.