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Date: Tue, 5 Sep 2023 18:00:33 +0000
From: Peter Todd <pete@petertodd.org>
To: Andrew Poelstra <apoelstra@wpsoftware.net>,
Bitcoin Protocol Discussion <bitcoin-dev@lists.linuxfoundation.org>
Message-ID: <ZPdswQ7uAJr35YbC@petertodd.org>
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Subject: Re: [bitcoin-dev] Compressed Bitcoin Transactions
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On Fri, Sep 01, 2023 at 01:56:18PM +0000, Andrew Poelstra via bitcoin-dev w=
rote:
> We can swag what the space savings would be: there are 122MM utxos right
> now, which is a bit under 2^27. So assuming a uniform distribution of
> prefixes we'd need to specify 28 bits to identify a UTXO. To contrast,
> to identify a blockheight we need 20 bits and then maybe 12 more bits to
> specify a TXO within a block. Plus whatever varint overhead we have.
> (I've been working on this project but busy with family stuff and don't
> remember exactly where we landed on the varints for this. I think we
> agreed that there was room for improvement but didn't want to hold up
> posting the rest of the concept because of it.)
Since most transactions spend txouts that are similar in height to each oth=
er,
you could save further bits by specifying a reference height and then encod=
ing
the exact txout with a delta.
If you're sending multiple txins or multiple transactions in a single packe=
t,
you could achieve this by starting the packet with the reference block heig=
ht.
If your application tends to send just a single transaction, you could use a
reference height that is a function of the current time. Since sender and
receiver might not agree on the exact time, you could try slightly differen=
ce
reference heights via bruteforcing until the transaction signatures validat=
e.
--=20
https://petertodd.org 'peter'[:-1]@petertodd.org
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