Subject: Re: [bitcoin-dev] A Better MMR Definition

From: Peter Todd <[email-masked]>
Date: Thu, 23 Feb 2017 21:58:11 -0500

On Thu, Feb 23, 2017 at 06:50:10PM -0800, Bram Cohen wrote:
> On Thu, Feb 23, 2017 at 5:09 PM, Peter Todd <[email-masked]> wrote:
> 
> > I think you've misunderstood what TXO commitments are. From my article:
> >
> > "A merkle tree committing to the state of all transaction outputs, both
> > spent
> > and unspent, can provide a method of compactly proving the current state
> > of an
> > output."
> > -https://petertodd.org/2016/delayed-txo-commitments#txo-commitments:
> >
> 
> The proposal on that page is of a tree which does require random access
> updates, it just positions entries in the order they happened to be added
> instead of sorting by their hash. Once you start updating it to indicate
> spent status all the exact same issues of TXO size and cache coherence on
> updates show up again, but now you're using a more complex bespoke data
> structure instead of a basic fundamental one.

Sorry, but I was replying to your statement:

> What you can't do with MMRs or the blockchain is make a compact proof that
> something is still in the utxo set, which is the whole point of utxo
> commitments.

So to be clear, do you agree or disagree with me that you *can* extract a
compact proof from a MMR that a given output is unspent?

I just want to make sure we're on the same page here before we discuss
performance characteristics.

-- 
https://petertodd.org 'peter'[:-1]@petertodd.org