Private Data Collections: Enabling Data Privacy in Permissioned Blockchains
TL;DR
It is proved that on-chain hashes form a conflict-complete proxy for private state—optimistic concurrency control (OCC) based serializability checks on hashed state detect exactly the same conflicts as checks on the underlying data, enabling the entire network to verify private transactions without accessing private data.
Abstract
Blockchain transparency poses a barrier to enterprise adoption in domains requiring data privacy. We introduce private data collections , a mechanism for permissioned blockchains that decouples private data storage from the replicated ledger: private data is shared only among authorized peers, while cryptographic hashes are recorded on-chain for tamper-evidence and serializability verification. Our key theoretical contribution is blind validation : we prove that on-chain hashes form a conflict-complete proxy for private state—optimistic concurrency control (OCC) based serializability checks on hashed state detect exactly the same conflicts as checks on the underlying data, enabling the entire network to verify private transactions without accessing private data. A three-component dissemination protocol—proactive push, reactive pull, and background reconciliation—ensures data availability. The design targets any blockchain following the simulate-order-validate-commit protocol. We implement it in Hyperledger Fabric with only 3–14% throughput overhead. The mechanism has been in production since Fabric v1.2, with deployments spanning food traceability, pharmaceuticals, aerospace, financial services, and global shipping.