To: =?UTF-8?Q?Jorge_Tim=c3=b3n?= <jtimon@jtimon.cc>
References: <CABm2gDr2-MCiaFFjgUFP5Xc0fQfuqJ3=ZkrzjHqmOiwRZ50CBw@mail.gmail.com>
From: Eric Voskuil <eric@voskuil.org>
Message-ID: <d58ee114-00fd-23c8-9ca7-9a4b28c26f27@voskuil.org>
Date: Wed, 16 Nov 2016 16:10:07 -0800
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Cc: Bitcoin Protocol Discussion <bitcoin-dev@lists.linuxfoundation.org>,
	Thomas Kerin <me@thomaskerin.io>
Subject: Re: [bitcoin-dev] BIP30 and BIP34 interaction (was Re: [BIP
 Proposal] Buried Deployments)
Precedence: list

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No, BIP30 prevents duplicate tx hashes in the case where the new tx hash
duplicates that of a preceding tx with unspent outputs.

There was one such case that had already become buried in the chain at
the time, so it was exempted from validation. There was another case of
a duplicate hash, but it's predecessor was spent so it complied with the
new rule.

Both of these cases resulted from exact duplicate txs, which BIP34 now
precludes. However nothing precludes different txs from having the same
hash.

e

On 11/16/2016 04:06 PM, Jorge Tim=C3=B3n wrote:
> On Thu, Nov 17, 2016 at 1:00 AM, Eric Voskuil <eric@voskuil.org> wrote:=

>> This is a misinterpretation of BIP30. Duplicate transaction hashes can=

>> and will happen and are perfectly valid in Bitcoin. BIP34 does not
>> prevent this.
>=20
> Sorry for moving the topic, but isn't duplication of tx hashes
> precisely what BIP30 prevents?
> That was my undesrtanding but should read it again.
> Since regular txs take inputs, the collision is extremely unlikely
> (again, this is my understanding, please correct me when wrong), the
> worrying case is coinbase txs (which don't have input to take entropy
> from). By introducing the committed height, collisions on coinbase txs
> are prevented too.
>=20
> If I'm wrong on any of this I'm more than happy to learn why.
>=20


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