Subject: Re: [bitcoin-dev] segwit subsidy and multi-sender (coinjoin) transactions

From: Peter Todd <[email-masked]>
Date: Mon, 2 May 2016 22:05:11 -0400

On Fri, Apr 29, 2016 at 02:22:32PM -0400, Kristov Atlas via bitcoin-dev wrote:
> A sample of the 16 transaction id's posted in the JoinMarket thread on
> BitcoinTalk shows an average ratio of 1.38 or outputs to inputs:
> 
> https://docs.google.com/spreadsheets/d/1p9jZYXxX1HDtKCxTy79Zj5PrQaF20mxbD7BAuz0KC8s/edit?usp=sharing
> 
> As we know, a "traditional" CoinJoin transaction creates roughly 2x UTXOs
> for everyone 1 it consumes -- 1 spend and 1 change -- unless address reuse
> comes into play.

Note how this is obviously an unsustainable situation - at some point that
change needs to be combined again, or you're throwing away money in the form of
UTXO's that aren't ever getting spent.

Meanwhile, if you put it another way the segwit discount is an obvious
advantage for coinjoin: by making spending UTXO's cheaper, we can recover those
funds that would otherwise get lost to dust, becoming ever more difficult to
spend.

-- 
https://petertodd.org 'peter'[:-1]@petertodd.org