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From: Yuval Kogman <nothingmuch@woobling.org>
Date: Fri, 19 Jul 2019 17:45:17 +0000
Message-ID: <CAAQdECAyQB0E0PxwBOxXoEtQO_HU5b3JGQpsqp_OfB8dOKqiUQ@mail.gmail.com>
To: Mike Brooks <m@ib.tc>, 
	Bitcoin Protocol Discussion <bitcoin-dev@lists.linuxfoundation.org>
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Subject: Re: [bitcoin-dev] PubRef - Script OP Code For Public Data References
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Hi,

On Fri, 19 Jul 2019 at 14:00, Mike Brooks via bitcoin-dev <
bitcoin-dev@lists.linuxfoundation.org> wrote:

Giving scripts the ability to refer to data on the blockchain will reduce
> transaction sizes because key material does not have to be repeated in
> every Script.
>

Given that address reuse is discouraged, and as far as I know is
predominantly utilized for customer deposit addresses by exchanges, many of
which have not invested resources in batching withdrawals or consolidating
small UTXOs, I am skeptical that such a feature would actually be utilized
by users for whom a potential use exists, especially as mining fees are
usually pushed onto customers anyway.

Unless extensively utilized such that costs outweigh benefits, this change
would impose an externality on validating nodes:

With this list a newly created script can refer to a specific PUSHDATA that
> was used in any previously confirmed block.
>

This would make pruning impossible, and also relaxes the bounds on
validation costs since it would allow random reads on all historical data
as opposed to just the UTXO set.

Although it would do nothing for block capacity, perhaps this redundancy
might be better addressed as opt-in functionality in the p2p layer? It
might help with IBD, though at least in my experience peer latency (as
opposed to throughput) is the limiting factor, and as far as I can tell
this would increase it. Somewhat relatedly, transaction IDs are another
type of pointer which might benefit from being encoded as a (block height,
offset). However, here too it seems to me like the complexity is
substantial, potentially introducing new DoS vectors, while saving several
bytes per input at most.

Regards,
Yuval

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<div dir=3D"ltr">Hi,<br><div><br><div class=3D"gmail_quote"><div dir=3D"ltr=
" class=3D"gmail_attr">On Fri, 19 Jul 2019 at 14:00, Mike Brooks via bitcoi=
n-dev &lt;<a href=3D"mailto:bitcoin-dev@lists.linuxfoundation.org">bitcoin-=
dev@lists.linuxfoundation.org</a>&gt; wrote:<br></div><br><blockquote class=
=3D"gmail_quote" style=3D"margin:0px 0px 0px 0.8ex;border-left:1px solid rg=
b(204,204,204);padding-left:1ex"><div dir=3D"ltr"><p dir=3D"ltr" style=3D"l=
ine-height:1.38;margin-top:0pt;margin-bottom:0pt"><span style=3D"font-size:=
11pt;font-family:Arial;color:rgb(0,0,0);background-color:transparent;font-v=
ariant-numeric:normal;font-variant-east-asian:normal;vertical-align:baselin=
e;white-space:pre-wrap">Giving scripts the ability to refer to data on the =
blockchain will reduce transaction sizes because key material does not have=
 to be repeated in every Script.</span></p></div></blockquote><div><br></di=
v><div>Given that address reuse is discouraged, and as far as I know is pre=
dominantly utilized for customer deposit addresses by exchanges, many of wh=
ich have not invested resources in batching withdrawals or consolidating sm=
all UTXOs, I am skeptical that such a feature would actually be utilized by=
 users for whom a potential use exists, especially as mining fees are usual=
ly pushed onto customers anyway.</div><div><br></div><div>Unless extensivel=
y utilized such that costs outweigh benefits, this change would impose an e=
xternality on validating nodes:<br></div><div><br></div><div><div><div clas=
s=3D"gmail_quote"><blockquote class=3D"gmail_quote" style=3D"margin:0px 0px=
 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div di=
r=3D"ltr"><p dir=3D"ltr" style=3D"line-height:1.38;margin-top:0pt;margin-bo=
ttom:0pt"><span style=3D"font-size:11pt;font-family:Arial;color:rgb(0,0,0);=
background-color:transparent;font-variant-numeric:normal;font-variant-east-=
asian:normal;vertical-align:baseline;white-space:pre-wrap">With this list a=
 newly created script can refer to a specific PUSHDATA that was used in any=
 previously confirmed block.</span></p></div></blockquote></div><br><div cl=
ass=3D"gmail_quote">This
 would make pruning impossible, and also relaxes=20
the bounds on validation costs since it would allow random reads on=20
all historical data as opposed to just the UTXO set.<br></div></div></div><=
div><br></div></div><div class=3D"gmail_quote">Although it would do nothing=
 for block capacity, perhaps this redundancy might be better addressed as o=
pt-in functionality in the p2p layer? It might help with IBD, though at lea=
st in my experience peer latency (as opposed to throughput) is the limiting=
 factor, and as far as I can tell this would increase it. Somewhat relatedl=
y, transaction IDs are another type of pointer which might benefit from bei=
ng encoded as a (block height, offset). However, here too it seems to me li=
ke the complexity is substantial, potentially introducing new DoS vectors, =
while saving several bytes per input at most.</div><div class=3D"gmail_quot=
e"><br></div><div class=3D"gmail_quote">Regards,</div><div class=3D"gmail_q=
uote">Yuval<br></div></div></div>

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