public inbox for bitcoindev@googlegroups.com
 help / color / mirror / Atom feed
From: Rusty Russell <rusty@rustcorp.com.au>
To: Gregory Maxwell <greg@xiph.org>, Pieter Wuille <pieter.wuille@gmail.com>
Cc: Bitcoin Dev <bitcoin-dev@lists.linuxfoundation.org>
Subject: Re: [bitcoin-dev] Rolling UTXO set hashes
Date: Tue, 23 May 2017 14:17:48 +0930	[thread overview]
Message-ID: <8760gs2n7v.fsf@rustcorp.com.au> (raw)
In-Reply-To: <CAAS2fgQKOKY6DEwY3ycMjysU5Xf2UUE+k=vg2ekkAMO7KG3Gsw@mail.gmail.com>

Gregory Maxwell via bitcoin-dev <bitcoin-dev@lists.linuxfoundation.org> writes:
> On Tue, May 16, 2017 at 6:17 PM, Pieter Wuille <pieter.wuille@gmail.com> wrote:
>> just the first - and one that has very low costs and no normative
>> datastructures at all.
>
> The serialization of the txout itself is normative, but very minimal.

I do prefer the (2) approach, BTW, as it reuses existing primitives, but
I know "simpler" means a different thing to mathier brains :)

Since it wasn't explicit in the proposal, I think the txout information
placed in the hash here is worth discussing.

I prefer a simple txid||outnumber[1], because it allows simple validation
without knowing the UTXO set itself; even a lightweight node can assert
that UTXOhash for block N+1 is valid if the UTXOhash for block N is
valid (and vice versa!) given block N+1.  And miners can't really use
that even if they were to try not validating against UTXO (!) because
they need to know input amounts for fees (which are becoming
significant).

If I want to hand you the complete validatable UTXO set, I need to hand
you all the txs with any unspent output, and some bitfield to indicate
which ones are unspent.

OTOH, if you serialize more (eg. ...||amount||scriptPubKey ?), then the UTXO
set size needed to validate the utxohash is a little smaller: you need
to send the txid, but not the tx nVersion, nLocktime or inputs.  But in a
SegWit world, that's actually *bigger* AFAICT.

Thanks,
Rusty.

[1] I think you could actually use txid^outnumber, and if that's not a
    curve point SHA256() again, etc.  But I don't think that saves any
    real time, and may cause other issues.


  reply	other threads:[~2017-05-23  4:58 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-05-15 20:01 [bitcoin-dev] Rolling UTXO set hashes Pieter Wuille
2017-05-15 20:53 ` Peter R
2017-05-15 23:04 ` ZmnSCPxj
2017-05-15 23:59   ` Gregory Maxwell
2017-05-16  0:15     ` ZmnSCPxj
2017-05-16 11:01     ` Peter Todd
2017-05-16 18:17       ` Pieter Wuille
2017-05-16 18:20         ` Gregory Maxwell
2017-05-23  4:47           ` Rusty Russell [this message]
2017-05-23 20:43             ` Pieter Wuille

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=8760gs2n7v.fsf@rustcorp.com.au \
    --to=rusty@rustcorp.com.au \
    --cc=bitcoin-dev@lists.linuxfoundation.org \
    --cc=greg@xiph.org \
    --cc=pieter.wuille@gmail.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox