From: Peter Todd <pete@petertodd•org>
To: Gregory Maxwell <greg@xiph•org>,
Bitcoin Protocol Discussion
<bitcoin-dev@lists•linuxfoundation.org>
Subject: Re: [bitcoin-dev] Fwd: "Compressed" headers stream
Date: Mon, 4 Sep 2017 10:06:44 -0400 [thread overview]
Message-ID: <20170904140644.GF1276@fedora-23-dvm> (raw)
In-Reply-To: <CAAS2fgRvSZm-NVLU++0WmWoaYbpX1R0Fqmv_Jf7a_RsqzXfOog@mail.gmail.com>
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On Mon, Aug 28, 2017 at 05:12:15PM +0000, Gregory Maxwell via bitcoin-dev wrote:
> You are leaving a lot of bytes on the table.
>
> The bits field can only change every 2016 blocks (4 bytes per header),
> the timestamp can not be less than the median of the last 11 and is
> usually only a small amount over the last one (saves 2 bytes per
> header), the block version is usually one of the last few (save 3
> bytes per header).
>
> But all these things improvements are just a constant factor. I think
> you want the compact SPV proofs described in the appendix of the
> sidechains whitepaper which creates log scaling proofs.
Note that I'm already planning on OpenTimestamps having infrastructure for
trusted validity attestations; log scaling proofs alone only prove total work,
not validity. Timestamping has all kinds of very dubious security properties
when done via proof-of-work, due to various ways that miners can get away with
inaccurate block times. In particular, setting a block time backwards is
something that miners can do, particularly with majority hashing power, which
is the exact thing we're trying to prevent in a timestamp proof.
This all makes me dubious about risking further weakening of this already weak
security with compact SPV proofs; we'd need a lot more analysis to understand
what we're risking. Also note that we can ship a known-good
sum-merkle-tree tip hash with the software, which further reduces initial
download bandwidth needed to get the block headers on top of this obviously
safe eliding of redundant hashes.
--
https://petertodd.org 'peter'[:-1]@petertodd.org
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prev parent reply other threads:[~2017-09-04 18:42 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-08-28 15:50 [bitcoin-dev] " Riccardo Casatta
2017-08-28 16:13 ` Greg Sanders
2017-08-28 16:25 ` Riccardo Casatta
2017-08-28 16:26 ` Greg Sanders
2017-09-04 14:10 ` Peter Todd
[not found] ` <CAAS2fgS3uG=4vgFuObPKA_5MstoGm4AabO=60fhV3EU_0dvejg@mail.gmail.com>
2017-08-28 17:12 ` [bitcoin-dev] Fwd: " Gregory Maxwell
2017-08-28 17:54 ` Kalle Rosenbaum
2017-09-04 14:06 ` Peter Todd [this message]
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