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Sender: gmaxwell@gmail.com
From: Gregory Maxwell <greg@xiph.org>
Date: Wed, 13 Sep 2017 09:39:28 +0000
Message-ID: <CAAS2fgTGhCztV5bwLQj28_M7e=uzwbdF2Rum_7gmQGjhgxqLuQ@mail.gmail.com>
To: Peter Todd <pete@petertodd.org>, 
	Bitcoin Protocol Discussion <bitcoin-dev@lists.linuxfoundation.org>
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Subject: [bitcoin-dev] Minutia in CT for Bitcoin. Was: SF proposal: prohibit
 unspendable outputs with amount=0
Precedence: list

On Wed, Sep 13, 2017 at 9:24 AM, Peter Todd via bitcoin-dev
<bitcoin-dev@lists.linuxfoundation.org> wrote:
> 2) Spending CT-shielded outputs to unshielded outputs
>
> Here one or more CT-shielded outputs will be spent. Since their value is zero,
> we make up the difference by spending one or more outputs from the CT pool,
> with the change - if any - assigned to a CT-pool output.

Can we solve the problem that pool inputs are gratuitously non-reorg
safe, without creating something like a maturity limit for shielded to
unshielded?

So far the best I have is this:  Support unshielded coins in shielded
space too. So the only time you transition out of the pool is paying
to a legacy wallet.  If support were phased in (e.g. addresses that
say you can pay me in the pool after its enabled), and the pool only
used long after wallets supported getting payments in it, then this
would be pretty rare and a maturity limit wouldn't be a big deal.

Can better be done?