Date: Fri, 7 Sep 2018 05:51:35 -0700
From: Brandon Smith <freedom@reardencode.com>
To: Alejandro Ranchal Pedrosa <a.ranchalpedrosa@gmail.com>
Message-ID: <20180907125135.GR62902@hank.reardencode.com>
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Cc: Bitcoin Protocol Discussion <bitcoin-dev@lists.linuxfoundation.org>,
	Onder.GURCAN@cea.fr
Subject: Re: [bitcoin-dev] A BIP proposal for transactions that are
 'cancellable'
Precedence: list

I believe you may be missing the overall points in the "Nail In the
Coffin" and "Temporary Discussion" sections. In summary:

1: Any UTXO spending a script with an expiration must be treated
similarly to Coinbase (I proposed a solution to this, but it's complex
and may have unforeseen implications).

2: All existing software assumes that a transaction once valid stays
valid. Any proposal to change this must ensure that existing wallets and
users aren't immediately open to being scammed by malicious actors
sending low fee expiring transactions.

The more tenable ways to move forward on improving the ecosystem around
delayed transactions and refunds are: Lightning, improved fee
estimation, and improved mempool eviction / re-propagation resistance.

The original reason that I began looking into this is because I noticed
that during high fee periods, transactions could re-propagate between
mempools of differing policies resulting in coins being stuck unusable
for far longer than the expected 1-2 week eviction. I don't know of any
concrete work going into investigating or improving this.

HTH,

--Brandon

On 2018-09-07 (Fri) at 09:12:40 +0200, Alejandro Ranchal Pedrosa wrote:
> Hi all,
> 
> Thank you for the link, and also to Gregory for the remarks. I did not 
> know about this previous proposal. I think the last paragraph of future 
> work is interesting:
> 
> "It may be interesting to add enhance OP_CHECKSEQUENCEVERIFY 
> <https://github.com/bitcoin/bips/blob/master/bip-0112.mediawiki> to 
> allow outputs that are spendable by Alice until time foo, always 
> spendable by Bob, and spendable by Joe only after time bar, or other 
> such cases"
> 
> Perhaps it would allow this functionality, while keeping the validity of 
> coins, if the new OP_zzz took an additional argument than suggested, 
> such that the first one is the timelimit for Alice to keep the coin (say 
> in the first 24 hours), and after those 24 hours the ownership goes to 
> the third argument, say Bob.
> 
> That is, it is not possible to use only specifying the owner in the 
> first 24 hours. Would this be considered harmful?
> 
> Best,
> 
> Alejandro.
> 
> On 9/6/18 10:32 PM, Brandon Smith wrote:
> > ade a similar proposal about 7 months ago, and documented some of the
> > discussion points here: