To: Anthony Towns <aj@erisian.com.au>,
	Bitcoin Protocol Discussion <bitcoin-dev@lists.linuxfoundation.org>,
	Christian Decker <decker.christian@gmail.com>
References: <87wodp7w9f.fsf@gmail.com>
	<20191001155929.e2yznsetqesx2jxo@erisian.com.au>
From: s7r <s7r@sky-ip.org>
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Message-ID: <51d80db6-83d9-2473-d007-f3601c940f28@sky-ip.org>
Date: Wed, 2 Oct 2019 18:11:25 +0300
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In-Reply-To: <20191001155929.e2yznsetqesx2jxo@erisian.com.au>
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Cc: lightning-dev@lists.linuxfoundation.org
Subject: Re: [bitcoin-dev] Continuing the discussion about noinput /
 anyprevout
Precedence: list

This is an OpenPGP/MIME signed message (RFC 4880 and 3156)
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From: s7r <s7r@sky-ip.org>
To: Anthony Towns <aj@erisian.com.au>,
 Bitcoin Protocol Discussion <bitcoin-dev@lists.linuxfoundation.org>,
 Christian Decker <decker.christian@gmail.com>
Cc: lightning-dev@lists.linuxfoundation.org
Message-ID: <51d80db6-83d9-2473-d007-f3601c940f28@sky-ip.org>
Subject: Re: [bitcoin-dev] Continuing the discussion about noinput /
 anyprevout
References: <87wodp7w9f.fsf@gmail.com>
 <20191001155929.e2yznsetqesx2jxo@erisian.com.au>
In-Reply-To: <20191001155929.e2yznsetqesx2jxo@erisian.com.au>

--D1yworrtRopo0MAMctdVVLhkFtIsbt14G
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Content-Language: en-US
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Anthony Towns via bitcoin-dev wrote:
[SNIP]
>=20
> My thinking at the moment (subject to change!) is:
>=20
>  * anyprevout signatures make the address you're signing for less safe,=

>    which may cause you to lose funds when additional coins are sent to
>    the same address; this can be avoided if handled with care (or if yo=
u
>    don't care about losing funds in the event of address reuse)
>=20

It's not necessarily like this. Address re-use is many times OUTSIDE the
control of the address owner. Say I give my address to a counterparty.
They send me a transaction which I successfully spend. So far so good.

After that, I have no control over that counterparty. If they decide to
re-use that address, it does not mean I wanted to re-use it and it also
does not mean that I don't care about those funds being lost.

This could create a lot of problems in the industry and I think it
should be avoided. Address re-use has been strongly discouraged ever
since I can remember, and all (proper) wallet implementations try as
hard as possible to enforce it, but it's not always possible. A
counterparty that decides to re-use an address, either accidentally or
not, is not under the control of the user who handed out the address in
the first place.

There are also a lot of use cases with P2SH addresses that are some
smart contracts particularly designed to be re-used multiple times over
time.

My 2 cents are that this is not a good way to go. If you try to index
the entire blockchain until now you'll see that address re-use is more
common than we'd want it to be and there's no clear way to prevent this
from further happening without hurting the economic interests of the user=
s.


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