MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8;
 format=flowed
Content-Transfer-Encoding: 8bit
Date: Tue, 29 Sep 2015 11:59:05 -0400
From: jl2012@xbt.hk
To: "Jonathan Toomim (Toomim Bros)" <j@toom.im>
In-Reply-To: <40B097BA-A389-4C46-B5DE-2EC4738086BA@toom.im>
References: <20150927185031.GA20599@savin.petertodd.org>
	<CA+w+GKRCVr-9TVk66utp7xLRgTxNpxYoj3XQE-6y_N8JS6eO6Q@mail.gmail.com>
	<20150928132127.GA4829@savin.petertodd.org>
	<CA+w+GKTCZDNVJ-XEmsCAWGXUV3xOzVYmqMQYm0x+ihyYWQN0Gg@mail.gmail.com>
	<20150928142953.GC21815@savin.petertodd.org>
	<CA+w+GKTUz2eVJOpixSebWiQ59ovoELNhsZWSsbLHXWqk2eCn0A@mail.gmail.com>
	<20150928144318.GA28939@savin.petertodd.org>
	<40B097BA-A389-4C46-B5DE-2EC4738086BA@toom.im>
Message-ID: <5e90be1b8f85cd46ed20eae84c062702@xbt.hk>
User-Agent: Roundcube Webmail/1.0.5
Cc: Bitcoin Dev <bitcoin-dev@lists.linuxfoundation.org>
Subject: Re: [bitcoin-dev] Let's deploy BIP65 CHECKLOCKTIMEVERIFY!
Precedence: list

Jonathan Toomim (Toomim Bros) via bitcoin-dev 於 2015-09-29 09:30 寫到:
> SPV clients will appear to behave normally, and
> will continue to show new transactions and get confirmations in a
> timely fashion. However, they will be systematically susceptible to
> attack from double-spends that attempt to spend funds in a way that
> the upgraded nodes will reject. These transactions will appear to get
> 1 confirmation, then regress to zero conf, every single time. These
> attacks can be performed for as long as someone mines with the old
> version.

1. Who told you to accept 1-confirmation tx? Satoshi recommended 6 
confirmations in the whitepaper. Take your own risk if you do not follow 
his advice.

2. This is true only if your SPV client naively follows the longest 
chain without even looking at the block version. This might be good 
enough for the 1st generation SPV client, but future generations should 
at least have basic fraud detecting mechanism.


> If an attacker thinks he could get more than 25 BTC of
> double-spends per block, he might even choose to mine with the
> obsolete version in order to get predictable orphans and to trick SPV
> clients and fully verifying wallets on the old version.

This point is totally irrelevant. No matter there is a softfork or not, 
SPV users are always vulnerable to such double-spending attack if they 
blindly follow the longest chain AND accept 1-confirmation. The fiat 
currency system might be safer for them.