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	<20170522140919.GA17878@fedora-23-dvm>
From: Ethan Heilman <eth3rs@gmail.com>
Date: Mon, 22 May 2017 10:41:40 -0400
Message-ID: <CAEM=y+XbHsCQ__u-oVqp8AjWoR29G45ZRDRDdFAMYJhqtRN0Pg@mail.gmail.com>
To: Peter Todd <pete@petertodd.org>
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Cc: Bitcoin Dev <bitcoin-dev@lists.linuxfoundation.org>
Subject: Re: [bitcoin-dev] A proposal to reintroduce the disabled script
	opcodes
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>It'd help your case if you gave us some examples of such scripts being
used.

I want OP_CAT so that I can securely and compactly verify many hashes and
hash preimages. This would shrink offchain Tumblebit transactions
significantly.

For instance if I want a transaction TxA which checks that a transaction
TxB releases preimages x1,x2,...,x10 such that
y1=H(x1), y2=H(x2),...,y10=H(x10). Currently I just put y1,...y10 and check
that the preimahes hash correctly. With OP_CAT I would only have to store
one hash in TxA, yhash

ytotal = H(OP_CAT(H(OP_CAT(y1, y2)),y3)...y10)

TxA could then just hash all the preimages supplied by TxB and confirm they
hash to TxA. This would reduce the size of TxA from approx 10*32B to
32+10*16B. I have a version which improves this further but it is more
complex.

Most of the math OP codes aren't particularly helpful due to their 32bit
nature and their strange overflow behavior.

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<div dir=3D"auto"><div dir=3D"auto">&gt;<span style=3D"font-family:sans-ser=
if">It&#39;d help your case if you gave us some examples of such scripts be=
ing used.</span></div><div dir=3D"auto"><br></div><div>I want OP_CAT so tha=
t I can securely and compactly verify many hashes and hash preimages. This =
would shrink offchain Tumblebit transactions significantly.<div dir=3D"auto=
"><br></div><div dir=3D"auto">For instance if I want a transaction TxA whic=
h checks that a transaction TxB releases preimages x1,x2,...,x10 such that<=
/div><div dir=3D"auto">y1=3DH(x1), y2=3DH(x2),...,y10=3DH(x10). Currently I=
 just put y1,...y10 and check that the preimahes hash correctly. With OP_CA=
T I would only have to store one hash in TxA, yhash</div><div dir=3D"auto">=
<br></div><div dir=3D"auto">ytotal =3D H(OP_CAT(H(OP_CAT(y1, y2)),y3)...y10=
)</div><div dir=3D"auto"><br></div><div dir=3D"auto">TxA could then just ha=
sh all the preimages supplied by TxB and confirm they hash to TxA. This wou=
ld reduce the size of TxA from approx 10*32B to 32+10*16B. I have a version=
 which improves this further but it is more complex.</div><div class=3D"gma=
il_extra"><div class=3D"gmail_quote"><br></div><div class=3D"gmail_quote" d=
ir=3D"auto">Most of the math OP codes aren&#39;t particularly helpful due t=
o their 32bit nature and their strange overflow behavior.</div></div></div>=
</div>

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