On Fri, Jun 05, 2026 at 05:54:50PM +1000, Anthony Towns wrote:
> On Thu, Jun 04, 2026 at 11:01:25AM +0000, Peter Todd wrote:
> > Note that you can design a message signing scheme where you can use a 
> > pubkey to
> > sign a merkle tree of messages. In the case of a transaction, multiple
> > conflicting versions of the transaction with different fee rates.
> 
> There's a balance to be had between what's considered part of the message
> signing scheme versus what's part of the scripting language.
> 
> The scheme above could also be thought of as signing a single message
> "spend this utxo is valid if this script's conditions are meant",
> where the script is "or(fee <= 0.5, and(nSequence >= 100, fee <= 1.0),
> and(nSequence >= 1000, fee <= 30.0))"

No, that's a very different scheme. Also, I believe it is vulnerable to miners
simply picking the best possible fee rate for them; nSequence isn't big enough
to avoid being guessed.

Indeed, I neglected to point out something important in the above: you probably
want to include secret nonces (or similar) in each individual branch of the
signature tree, to ensure that different versions of it can't be brute forced.
Thus to reveal a new option for miners, you make public a previously secret
nonce. 128-bits would be sufficiently large to prevent brute-forcing.

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

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