Paper 2018/209

CALYPSO: Private Data Management for Decentralized Ledgers

Eleftherios Kokoris-Kogias, Enis Ceyhun Alp, Linus Gasser, Philipp Jovanovic, Ewa Syta, and Bryan Ford

Abstract

Distributed ledger technologies provide high availability and integrity, making them a key enabler for practical and secure computation of distributed workloads among mutually distrustful parties. However, many practical applications also require confidentiality, the third pillar of the CIA triad. In this work, we enhance permissioned and permissionless blockchains with the ability to manage confidential data without forfeiting availability or decentralization. More specifically, CALYPSO sets out to achieve two orthogonal goals that challenge modern distributed ledgers: (a) enable blockchains to auditably manage secrets and (b) protect distributed computations against arbitrage attacks when their results depend on the ordering and secrecy of inputs. To this end, CALYPSO proposes on-chain secrets, a novel abstraction that enforces atomic deposition of an auditable trace whenever users access confidential data. Furthermore, CALYPSO provides user-controlled consent management that ensures revocation atomicity and accountable anonymity. Finally, to enable the permissionless deployment of CALYPSO, we introduce an incentive scheme and provide users with the option to select their preferred trustees. We evaluated our CALYPSO prototype with a confidential document sharing application and a decentralized lottery. Our benchmarks show that the latency of processing transactions increases linearly to the added security (in number of trustees) and is in the range of 0.2 to 8 seconds for 16 to 128 trustees.