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From: Luke Dashjr <luke@dashjr.org>
To: bitcoin-dev@lists.linuxfoundation.org, Tom <tomz@freedommail.ch>
Subject: Re: [bitcoin-dev] BIP draft: OP_CHECKBLOCKATHEIGHT
Date: Fri, 23 Sep 2016 22:34:41 +0000	[thread overview]
Message-ID: <201609232234.43689.luke@dashjr.org> (raw)
In-Reply-To: <2403444.9CSRyRIcH2@garp>

Joe sends Alice 5 BTC (UTXO 0).
Fred sends Alice 4 BTC (UTXO 1).
Alice sends Bob 4 BTC using UTXO 1 (creating UTXO 2).
Fred double-spends UTXO 1 with UTXO 1-B. This invalidates Alice's transfer to 
Bob.
Alice has UTXO 0 which she can send to Bob (UTXO 3), but if she does so, it is 
possible that UTXO 0 could be mined, and then both UTXO 2 and UTXO 3 which 
would result in her giving Bob a total of 8 BTC rather than merely 4 BTC.
Even if Alice waits until Fred's UTXO 1-B confirms 10 blocks deep, it is not 
impossible for a reorganization to reverse those 10 blocks and confirm UTXO 1 
again.
Using OP_CHECKBLOCKATHEIGHT, however, Alice can create UTXO 3 such that it is 
valid only in the blockchain where Fred's UTXO 1-B has confirmed. This way, if 
that block is reorganized out, UTXO 3 is invalid, and either Bob receives only 
the original UTXO 2, or Alice can create a UTXO 3-B which is valid in the 
reorganized blockchain if it again confirms the UTXO 1-B double-spend.

Luke

On Friday, September 23, 2016 2:37:39 PM Tom via bitcoin-dev wrote:
> On Friday 23 Sep 2016 09:57:01 Luke Dashjr via bitcoin-dev wrote:
> > This BIP describes a new opcode (OP_CHECKBLOCKATHEIGHT) for the Bitcoin
> > scripting system to address reissuing bitcoin transactions when the coins
> > they spend have been conflicted/double-spent.
> > 
> > https://github.com/luke-jr/bips/blob/bip-cbah/bip-cbah.mediawiki
> 
> Can you walk us through a real live usecase which this solves?  I read it
> and I think I understand it, but I can't see the attack every giving the
> attacker any benefit (or the attacked losing anything).
> _______________________________________________
> bitcoin-dev mailing list
> bitcoin-dev@lists.linuxfoundation.org
> https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev


  reply	other threads:[~2016-09-23 22:35 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-09-23  9:57 [bitcoin-dev] BIP draft: OP_CHECKBLOCKATHEIGHT Luke Dashjr
2016-09-23 13:43 ` Russell O'Connor
     [not found]   ` <CAAS2fgQGC695mkyze+mVTZZoQN1mh+1y32u-D6Yv1R7nXWPDcg@mail.gmail.com>
2016-09-23 18:57     ` Gregory Maxwell
2016-09-23 20:02       ` Peter Todd
2016-09-23 22:20   ` Luke Dashjr
2016-09-23 23:43     ` Gregory Maxwell
2016-09-23 14:37 ` Tom
2016-09-23 22:34   ` Luke Dashjr [this message]
2016-09-24  0:08     ` Dave Scotese
2016-09-24  9:37     ` Tom
2016-09-23 16:18 ` Peter Todd
2016-10-01  4:01 ` Rusty Russell
2016-10-01  5:02   ` Luke Dashjr
2016-10-05  2:15     ` Nathan Cook

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