Ubiquitous adoption of cloud computing and virtualization technology has necessitated the need for strong security mechanisms. Multiple entities are involved in creating, exchanging, and altering data objects in the cloud environment, making it challenging to track malicious activities and security violations. To address these issues, there is a need for a data provenance framework, with which each data object in the federated cloud environment can be tracked and recorded. Although log-based provenance provides the ability to track operations conducted on digital assets, the provenance data are not transparent and immutable. Blockchain technology offers a promising mechanism for building a tamper-proof information system backed by strong cryptographic primitives. In this article, we propose BlockCloud, a blockchain-empowered data provenance architecture for the cloud computing platform. In addition, we present a proof-of-stake (PoS) consensus mechanism for BlockCloud to alleviate the overhead of computational requirements that the traditional proof-of-work (PoW) consensus needs. Finally, we discuss several research challenges and vulnerabilities that need to be addressed to realize BlockCloud.