Chronos+: An Accurate Blockchain-based Time-stamping Scheme for Cloud Storage

Abstract

We propose Chronos $^{{\mathbf +}}$ + , an accurate blockchain-based time-stamping scheme for outsourced data, where both the storage and time-stamping services are provided by cloud service providers. Specifically, Chronos $^{{\mathbf +}}$ + integrates a file into a transaction on a blockchain once the file is created, which guarantees the file's latest creation time to be the time when the block containing the transaction is appended to the blockchain. A sufficient number of consecutive blocks that are latest confirmed on the blockchain is embedded into the file at the creation time. These blocks serve as a time-dependent random seed to prove the earliest creation time, due to blockchains’ chain quality property. Chronos $^{{\mathbf +}}$ + makes the file's timestamp corresponding to a time interval formed by the earliest and latest creation times which are derived from the heights of the corresponding blocks. Due to blockchains’ chain growth property, such a height-derived timestamp can ensure that the time intervals’ range is within a few minutes so as to guarantee the accuracy. We also point out potential threats towards outsourced time-sensitive files and present security analyses to prove that Chronos $^{{\mathbf +}}$ + is secure against these threats. Comprehensive performance evaluations demonstrate the efficiency and practicality of Chronos $^{{\mathbf +}}$ + .