On Thu, 20 Dec 2018 03:47:11 -0500 grarpamp <grarpamp@gmail.com> wrote:
blockchain history is not really needed...
it isn't? So how do you verify supply? actually I should have asked - how do you know you have a valid utxo set? The whole point of downloading and validating a chain is to get a valid utxo set.
Consensus perhaps need not be confined only over tx into blocks, could be extended over other data and knowledge into blocks, such as of hashes over utxo set computed at checkpoints. Could utilize already trusted consensus mechanism (10 years and billions current value) to make skipping genesis validation possible... perhaps even tx stream feeding diffs to database consensus.
Alternatively, how do you know you have a valid genesis block and network view? PKI? MITM? Equivalent lols.
PoW difficulty of the entire chain. It takes enormous resources to produce an alternate chain dating back to the genesis block that is anywhere close to the difficulty of the BTC chain.
Read the papers for actual answers.
A node has to download the entire blockchain contents to verify that the UTXO set commitment is valid. You can require each miner to post this commitment, then have it a part of the consensus protocol, but that only tells you that your network peers didn't reject the UTXO commitment and nothing of its validity. The comment thread on /r/btc indicates that this is going to be used for a fast sync mode. The security, if the entire chain isn't downloaded, is equivalent to SPV but allows slightly more privacy. However, if people frequently spin up a fast sync node only when they want to transact, an ISP can easily log when they see bitcoin p2p traffic and look at the transactions in that given time window. This is an extreme case (for some), and is probably an improvement over the pure SPV methods which can leak information directly to the node providing the SPV client information. Lee