Cryptocurrency: BCH puts UTXO Set on IPFS, OpenSwap Atomic DEX, The 51%

[Lee Clagett]

On Thu, 20 Dec 2018 03:47:11 -0500
grarpamp <grarpamp at 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