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Date: Fri, 3 Oct 2025 16:12:27 +0000
From: Peter Todd <pete@petertodd.org>
To: Erik Aronesty <erik@q32.com>
Cc: bitcoindev@googlegroups.com
Subject: Re: [bitcoindev] OP_CHECKUTXOSETHASH idea
Message-ID: <aN_16-lBQzY5K9XL@petertodd.org>
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On Mon, Sep 29, 2025 at 05:09:15PM -0700, Erik Aronesty wrote:
> A soft fork could introduce a new opcode, `OP_CHECKUTXOSETHASH`, allowing
> miners to optionally commit a deterministic hash of the current UTXO set
> into a block. If present, all nodes must verify its correctness or reject
> the block; if absent, the block is still valid. Old nodes treat the opcode
> as unspendable, so backward compatibility is preserved.
>
> Because computing the full UTXO root is costly, this makes each checkpoint
> intentionally expensive to produce, ensuring that miners will only include
> them when compensated with sufficient fees. Additionally, it could be
> limited to one per block.
No, it's costly for everyone to compute: everyone needs to recompute this to
validate that the block is valid.
Anyway, just as an aside, if you really need to do something like this, make
the commitment be computable in advance by using a UTXO set root from the
*prior* interval, to give nodes plenty of time to compute it. I outlined this
approach before in the form of delayed txo commitments:
https://petertodd.org/2016/delayed-txo-commitments
--
https://petertodd.org 'peter'[:-1]@petertodd.org
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