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Date: Mon, 22 May 2017 12:14:04 -0400
From: Peter Todd <pete@petertodd.org>
To: Ethan Heilman <eth3rs@gmail.com>
Message-ID: <20170522161404.GA18885@fedora-23-dvm>
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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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On Mon, May 22, 2017 at 10:41:40AM -0400, Ethan Heilman wrote:
> >It'd help your case if you gave us some examples of such scripts being
> used.
>=20
> I want OP_CAT so that I can securely and compactly verify many hashes and
> hash preimages. This would shrink offchain Tumblebit transactions
> significantly.
>=20
> For instance if I want a transaction TxA which checks that a transaction
> TxB releases preimages x1,x2,...,x10 such that
> y1=3DH(x1), y2=3DH(x2),...,y10=3DH(x10). Currently I just put y1,...y10 a=
nd check
> that the preimahes hash correctly. With OP_CAT I would only have to store
> one hash in TxA, yhash
>=20
> ytotal =3D H(OP_CAT(H(OP_CAT(y1, y2)),y3)...y10)
>=20
> TxA could then just hash all the preimages supplied by TxB and confirm th=
ey
> 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.
>=20
> Most of the math OP codes aren't particularly helpful due to their 32bit
> nature and their strange overflow behavior.
Great! That's exactly the type of justifying use-case we need for a BIP.
An OP_CAT will have to have limits on maximum output size; how big an output
does your application need?
--=20
https://petertodd.org 'peter'[:-1]@petertodd.org
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