Subject: Re: [bitcoindev] Penlock, a paper-computer for secret-splitting BIP39 seed phrases

From: Andrew Poelstra <[email-masked]>
Date: Thu, 16 May 2024 17:24:26 +0000

On Thu, May 16, 2024 at 01:27:55PM +0000, Andrew Poelstra wrote:
> >
> > [3]: The 2-of-M wheel "Recovery" window shows the distance between two shares:
> > https://beta.penlock.io/2ofm-wheel.html
> >
> 
> Ah, I understand. Looking again at your wheel, I see that it's a
> combination slide wheel (for addition/subtraction) and slide chart (for
> "recovery windows").
> 
> What I'm saying is that you don't need to have extra cutout windows for
> the recovery windows. You should be able to just label the characters on
> the inner wheel with them, similar to how you have already labeled =
> with (1).
>

Ah, I am incorrect. You can put the recovery windows on a slide wheel
but it needs to use a different ordering than the one used for addition.
So you would need a second wheel and possibly some relabelling of
recovery windows.

I don't see why this is ... it seems that the recovery windows, being
differences of characters, should follow exactly the same pattern as
addition (possibly in the opposite direction). So worth investigating.

But assuming that it isn't possible and would require you introduce
another wheel, it's probably not worth the extra "simplicity". After
all, you only need to look up the windows once per share (so volvelle
ergonomics are not so important) and you only need to cut out as many
windows as you have shares (so setup/construction time is not bad).

-- 
Andrew Poelstra
Director, Blockstream Research
Email: apoelstra at wpsoftware.net
Web:   https://www.wpsoftware.net/andrew

The sun is always shining in space
    -Justin Lewis-Webster

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