To: Alex Morcos <morcos@gmail.com>,
	Bitcoin Protocol Discussion <bitcoin-dev@lists.linuxfoundation.org>
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	<e86b5b85-591d-5342-6a75-3ebd501f1789@thomaskerin.io>
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	<CAPWm=eWcZZCzKWXkX=sD=cnjTCEGmdN3G_hf85rwy60EAUXUqQ@mail.gmail.com>
From: Eric Voskuil <eric@voskuil.org>
Message-ID: <6b3837bb-cde9-87e9-5822-5405a6f7e2f7@voskuil.org>
Date: Wed, 16 Nov 2016 17:41:51 -0800
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Cc: Thomas Kerin <me@thomaskerin.io>
Subject: Re: [bitcoin-dev] [BIP Proposal] Buried Deployments
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On 11/16/2016 05:24 PM, Alex Morcos wrote:
> huh?
> can you give an example of how a duplicate transaction hash (in the sam=
e
> chain) can happen given BIP34?

"The pigeonhole principle arises in computer science. For example,
collisions are inevitable in a hash table because the number of possible
keys exceeds the number of indices in the array. A hashing algorithm, no
matter how clever, cannot avoid these collisions."

https://en.wikipedia.org/wiki/Pigeonhole_principle

e

> On Wed, Nov 16, 2016 at 7:00 PM, Eric Voskuil via bitcoin-dev wrote:
>=20
>     On 11/16/2016 03:58 PM, Jorge Tim=C3=B3n via bitcoin-dev wrote:
>     > On Wed, Nov 16, 2016 at 3:18 PM, Thomas Kerin via bitcoin-dev
>     > <bitcoin-dev@lists.linuxfoundation.org
>     <mailto:bitcoin-dev@lists.linuxfoundation.org>> wrote:
>     >> BIP30 actually was given similar treatment after a reasonable am=
ount of time
>     >> had passed.
>     >> https://github.com/bitcoin/bitcoin/blob/master/src/main.cpp#L239=
2
>     <https://github.com/bitcoin/bitcoin/blob/master/src/main.cpp#L2392>=

>     >
>     > This is not really the same. BIP30 is not validated after BIP34 i=
s
>     > active because blocks complying with BIP34 will always necessaril=
y
>     > comply with BIP30 (ie coinbases cannot be duplicated after they
>     > include the block height).
>=20
>     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
>     e


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