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>
References: <CAK9dXBSg+wzAZw7_xPXRVvx1uZzjAEE8nuvj0vkdSGD-yTfwhQ@mail.gmail.com>
	<20170522140919.GA17878@fedora-23-dvm>
	<CAEM=y+XbHsCQ__u-oVqp8AjWoR29G45ZRDRDdFAMYJhqtRN0Pg@mail.gmail.com>
MIME-Version: 1.0
Content-Type: multipart/signed; micalg=pgp-sha256;
	protocol="application/pgp-signature"; boundary="pWyiEgJYm5f9v55/"
Content-Disposition: inline
In-Reply-To: <CAEM=y+XbHsCQ__u-oVqp8AjWoR29G45ZRDRDdFAMYJhqtRN0Pg@mail.gmail.com>
User-Agent: Mutt/1.5.23 (2014-03-12)
Cc: Bitcoin Dev <bitcoin-dev@lists.linuxfoundation.org>
Subject: Re: [bitcoin-dev] A proposal to reintroduce the disabled script
 opcodes
Precedence: list


--pWyiEgJYm5f9v55/
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
Content-Transfer-Encoding: quoted-printable

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

--pWyiEgJYm5f9v55/
Content-Type: application/pgp-signature; name="signature.asc"
Content-Description: Digital signature

-----BEGIN PGP SIGNATURE-----

iQEcBAEBCAAGBQJZIw5JAAoJECSBQD2l8JH7330H/0KNsTfnDNlyZyQslncEptoh
LEYfziNSaxob3C3i7U9/4/bYBbRs7oVlDZa7ZDKnJC/PDfGvStDru1Gr+LwEQbwp
q4cJE0Y9tkVVmdsnpE859in5N2AUkk3lvMtbj+i0RS+MjdbE7S8JD4roUNP33wn0
JGtP7wbo/s6fqOmBbg9QTXYH0vZAYxXoPVJHAwUnWtvHXazgxSAv5kxQETYzEshZ
zJHr1MVD7X+uSjoC86Iyu3/Ej7BI/ASjznrJrjjJ3q3tTefTMG5qQrsnaODU4zkS
mhtskQQkFp5BQv75qXTxhCbRzK+x9PrkFxTEB+b0TuSzhy6ZTz1SnzuuvmjH7Zk=
=Pb87
-----END PGP SIGNATURE-----

--pWyiEgJYm5f9v55/--