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Date: Thu, 17 Dec 2015 22:10:02 -0500
From: jl2012 <jl2012@xbt.hk>
To: Jonathan Toomim <j@toom.im>
In-Reply-To: <E76D5BF9-41BF-4AF5-BBAC-06F4EF574EBE@toom.im>
References: <CAPg+sBjJcqeqGLHnPyWt23z3YoCRGozQupuMxy51J_-hdkKBSA@mail.gmail.com>
	<E76D5BF9-41BF-4AF5-BBAC-06F4EF574EBE@toom.im>
Message-ID: <6bc6451f3d9cfb5e5a1ba15356c229bc@xbt.hk>
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Cc: Bitcoin Dev <bitcoin-dev@lists.linuxfoundation.org>
Subject: Re: [bitcoin-dev] On the security of softforks
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Jonathan Toomim via bitcoin-dev 於 2015-12-17 21:47 寫到:
> Mallory wants to defraud Bob with a 1 BTC payment for some beer. Bob
> runs the old rules. Bob creates a p2pkh address for Mallory to use.
> Mallory takes 1 BTC, and creates an invalid SegWit transaction that
> Bob cannot properly validate and that pays into one of Mallory's
> wallets. Mallory then immediately spends the unconfirmed transaction
> into Bob's address. Bob sees what appears to be a valid transaction
> chain which is not actually valid.
> 
> Clueless Carol is one of the 4.9% of miners who forgot to upgrade her
> mining node. Carol sees that Mallory included an enormous fee in his
> transactions, so Carol makes sure to include both transactions in her
> block.
> 
> Mallory gets free beer.
> 
> Anything I'm missing?

You miss the fact that 0-conf is not safe, neither 1-conf. What you are 
suggesting is just a variation of Finney attack.