Lightning is all the rage these days and, while it's an exciting development, users currently have to have a full node running in order to transact in it. In this article, I'm going to introduce Neutrino, a new protocol for light clients to get the data that they need while preserving privacy and without trusting a central server.A Little HistoryIn the original white paper written in 2008, Satoshi Nakamoto described something called Simplified Payment Verification (SPV). SPV is how a light node can verify payments without downloading, verifying or storing the entire blockchain. This was supposed to be the basis of light wallets. Unfortunately, the original Bitcoin Core software did not implement Simplified Payment Verification, so light clients did not have access to the data necessary to do SPV in a privacy-preserving way.In 2013, BIP0037 was added to Bitcoin Core to make SPV viable. BIP0037 created network commands to make the Simplified Payment Verification possible for light nodes to do. Light nodes could now ask for proof that a particular transaction happened in a particular block. That way, light nodes wouldn't have to trust servers but could actually verify the data being given to them.To achieve this, the light client gives the server a filter. The server then runs the filter over all the transactions of a new block and reports back those transactions, along with proof that they&...
