The current UTXO-based blockchains require the validators to keep the entire ever-growing UTXO set to verify transactions, which is unsuitable for ordinary machines since they occupy a large size of RAM in the long run, resulting in network centralizations. Recently, stateless blockchain technology has been proposed which uses the accumulator to combine the large UTXO set into one short, constant-sized commitment. However, the UTXO commitments in these methods are inefficient since the UXTO set is required dynamic addition and removal of elements as transactions are processed. In this work, we propose MiniChain, which replaces the UTXO set with two append-only data structures: STXO (Spent Transaction Outputs) set and TXO (Transaction Outputs) set. Thus, a valid UTXO must belong to the TXO set, but not in STXO set. Then, we construct a novel STXO commitment and TXO commitment by using a trapdoor-less RSA accumulator and a Merkle Mountain Range (MMR) respectively, greatly increasing the efficiency of accumulator. Besides, we introduce a cache mechanism, by storing the STXOs of latest N blocks, the transaction proof can be kept alive for a period of time, avoiding constantly recomputing proofs for unaccepted transactions. Our evaluation shows that (i) MiniChain only needs a fixed-size RAM and the disk usage grows very slow since only the block headers are stored; (ii) comparing to the state-of-the-art work, the performance of the accumulator update has been improved from O(n(2)) to O(n), enabling MiniChain to support a higher TPS. (C) 2020 Elsevier Inc. All rights reserved.
