PPoS : Practical Proof of Storage for Blockchain Full Nodes

Abstract

Blockchain is a distributed and immutable ledger managed by all participants. The full nodes which store the entire ledger play an essential role in managing it in a transparent and decentralised manner. However, it is difficult to verify that full nodes store the entire ledger in their dedicated storage due to Sybil, outsourcing, or generation attacks. Existing work on proving storage for cloud computing and remote data storage applications has high latency for decryption, and its impact on decentralisation is unclear, rendering it impractical for use in blockchain. In this paper, we propose a decentralised Practical Proof of Storage (PPoS) solution for blockchain full nodes with asymmetric latencies for encryption and decryption, which introduces a chained encryption and decryption architecture. To generate a unique replica of a block, each full node performs encryption with its own address and a previously encrypted block, storing the unique block in its dedicated storage. In PPoS, encryption is expensive and time consuming, enabling it to detect outsourcing and generation attacks and to deter Sybil attacks. Simultaneously, decryption is about 25 times faster than encryption, resulting in minimal performance overhead. The proof process is also decentralised by randomly selecting provers, verifiers, and encrypted blocks. Our experiments use up to 720 real BitCoin blocks to evaluate the performance and quantify the decentralisation of PPoS. Our results show that PPoS's asymmetric design reduces decryption time 25-fold over existing approaches, while maintaining a high degree of decentralisation, confirming its suitability for blockchain full nodes.