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From: "Russell O'Connor" <roconnor@blockstream.com>
Date: Sat, 18 Feb 2023 13:03:45 -0500
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To: vjudeu@gazeta.pl, 
 Bitcoin Protocol Discussion <bitcoin-dev@lists.linuxfoundation.org>
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Subject: Re: [bitcoin-dev] Testing censorship resistance of bitcoin p2p
	network
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On Sat, Feb 18, 2023 at 5:11 AM vjudeu via bitcoin-dev <
bitcoin-dev@lists.linuxfoundation.org> wrote:

>
> Also, it gives us a hint, that if any Script upgrade will be considered in
> the future, we can think about doing it in a way, where unused parts can be
> pruned, without invalidating signatures.
>

FWIW, pruning unused case branches is a core design principle of the
Simplicity language I am developing.

That being said, even this is not enough to thwart agents that specifically
desire to post unused data blobs as part of their programs.  This is
largely because there are many mathematical expressions for what is
equivalently an identity function.  Think computing (x ^ 257) mod 257 (see
Fermat's little theorem).

Even in Simplicity users can write Word *<some data blob>*; unit which is
roughly equivalent PUSH *<data blob>* DROP in Script.  I don't even bother
trying to prevent it.  Doing so just adds more consensus complexity, and
only raises the bar slightly on how to work around it.

Simplicity's pruning is instead meant as a way to (usually) lower costs for
users who aren't actively trying to spam the network.

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<div dir=3D"ltr"><div class=3D"gmail_quote"><div dir=3D"ltr" class=3D"gmail=
_attr">On Sat, Feb 18, 2023 at 5:11 AM vjudeu via bitcoin-dev &lt;<a href=
=3D"mailto:bitcoin-dev@lists.linuxfoundation.org">bitcoin-dev@lists.linuxfo=
undation.org</a>&gt; wrote:<br></div><blockquote class=3D"gmail_quote" styl=
e=3D"margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);paddin=
g-left:1ex"><br>
Also, it gives us a hint, that if any Script upgrade will be considered in =
the future, we can think about doing it in a way, where unused parts can be=
 pruned, without invalidating signatures.<br></blockquote><div><br></div><d=
iv>FWIW, pruning unused case branches is a core design principle of the Sim=
plicity language I am developing.</div><div><br></div><div>That being said,=
 even this is not enough to thwart agents that specifically desire to post =
unused data blobs as part of their programs.=C2=A0 This is largely because =
there are many mathematical expressions for what is equivalently an identit=
y function.=C2=A0 Think computing (x ^ 257) mod 257 (see Fermat&#39;s littl=
e theorem).<br></div><div><br></div><div>Even in Simplicity users can write=
 <span style=3D"font-family:monospace">Word <i>&lt;some data blob&gt;</i>; =
unit</span> which is roughly equivalent <span style=3D"font-family:monospac=
e">PUSH <i>&lt;data blob&gt;</i> DROP</span> in Script.=C2=A0 I don&#39;t e=
ven bother trying to prevent it.=C2=A0 Doing so just adds more consensus co=
mplexity, and only raises the bar slightly on how to work around it.</div><=
div><br></div><div>Simplicity&#39;s pruning is instead meant as a way to (u=
sually) lower costs for users who aren&#39;t actively trying to spam the ne=
twork.<br></div></div></div>

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