Cloud services have turned remote computation into a commodity and enable convenient online collaboration. However, they require that clients fully trust the service provider in terms of confidentiality, integrity, and availability. Towards reducing this dependency, this paper introduces a protocol for verification of integrity and consistency for cloud object storage (VICOS), which enables a group of mutually trusting clients to detect data-integrity and consistency violations for a cloud object-storage service. It aims at services where multiple clients cooperate on data stored remotely on a potentially misbehaving service. VICOS enforces the consistency notion of fork-linearizability, supports wait-free client semantics for most operations, and reduces the computation and communication overhead compared to previous protocols. VICOS is based in a generic way on any authenticated data structure. Moreover, its operations cover the hierarchical name space of a cloud object store, supporting a real-world interface and not only a simplistic abstraction. A prototype of VICOS that works with the key-value store interface of commodity cloud storage services has been implemented, and an evaluation demonstrates its advantage compared to existing systems.
Several cloud storage systems exist today, but none of them provide security guarantees in their Service Level Agreements (SLAs). This lack of security support has been a major hurdle for the adoption of cloud services, especially for enterprises and cautious consumers. To fix this issue, we present CloudProof, a secure storage system specifically designed for the cloud. In CloudProof, customers can not only detect violations of integrity, write-serializability, and freshness, they can also prove the occurrence of these violations to a third party. This proof-based system is critical to enabling security guarantees in SLAs, wherein clients pay for a desired level of security and are assured they will receive a certain compensation in the event of cloud misbehavior. Furthermore, since CloudProof aims to scale to the size of large enterprises, we delegate as much work as possible to the cloud and use cryptographic tools to allow customers to detect and prove cloud misbehavior. Our evaluation of CloudProof indicates that its security mechanisms have a reasonable cost: they incur a latency overhead of only ∼15 on reads and writes, and reduce throughput by around 10 . We also achieve highly scalable access control, with membership management (addition and removal of members' permissions) for a large proprietary software with more than 5000 developers taking only a few seconds per month.