Near-stateless, fully parallelizable validation of the Bitcoin blockchain with hints about which outputs remain unspent. All other inputs/outputs are efficiently crossed off inside a single hash aggregate that only reaches zero if validation was successful and the hints were correct.
Validation is at the heart of Bitcoin. Any improvements in validation speed will have a direct impact on the scalability of the system, including everything that is built on top of it. For this reason improving validation performance may be one of the most important things we can do.
The generalized observation of SwiftSync is that if we have two sets (in this case the inputs and outputs), and we want to know the difference between these sets (the UTXO set), validating a given answer to this question (the hints) is significantly easier than calculating the answer itself. The novel part here (to my knowledge) is specifically how this can be applied to sets. It seems likely that this observation ca
