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Full nodes in a blockchain network store and verify a copy of the whole blockchain. Unlike full nodes, light clients are low-capacity devices that want to validate certain data on a blockchain. They query the data they want from a full node. If light clients do not verify the data they receive, full nodes might deceive them. SPV, introduced in the Bitcoin paper, is a practical solution to this problem currently used in many PoW blockchains. In SPV, the resources needed to verify a full node's response grow linearly with the blockchain size, making it inefficient over the long run. Another issue with SPV is that the full nodes do not get compensated for the services they provide. In this work, we introduce LightSync, a simple and cost-effective solution for light clients to verify the inclusion of certain data in a PoW blockchain. The resources needed for running LightSync remain constant no matter what the size of the blockchain is. LightSync uses an incentive mechanism that encourages full nodes to participate in the protocol. We perform a thorough analysis of the security of LightSync and discuss the details of deploying it in a real-world environment. |
