Re: [bitcoin-dev] BIP30 and BIP34 interaction (was Re: [BIP Proposal] Buried Deployments)

[Eric Voskuil <eric@voskuil.org>]

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> This means that all future transactions will have different txids...
rules do guarantee it.

No, it means that the chance is small, there is a difference.

If there is an address collision, someone may lose some money. If there
is a tx hash collision, and implementations handle this differently, it
will produce a chain split. As such this is not something that a node
can just dismiss. If they do they are implementing a hard fork.

e

On 11/16/2016 04:31 PM, Tier Nolan via bitcoin-dev wrote:
> 
> 
> On Thu, Nov 17, 2016 at 12:10 AM, Eric Voskuil via bitcoin-dev
> <bitcoin-dev@lists.linuxfoundation.org
> <mailto:bitcoin-dev@lists.linuxfoundation.org>> wrote:
> 
>     Both of these cases resulted from exact duplicate txs, which BIP34 now
>     precludes. However nothing precludes different txs from having the same
>     hash.
> 
> 
> The only way to have two transactions have the same txid is if their
> parents are identical, since the txids of the parents are included in a
> transaction.
> 
> Coinbases have no parents, so it used to be possible for two of them to
> be identical.
> 
> Duplicate outputs weren't possible in the database, so the later
> coinbase transaction effectively overwrote the earlier one.
> 
> The happened for two coinbases.  That is what the exceptions are for.
> 
> Neither of the those coinbases were spent before the overwrite
> happened.  I don't even think those coinbases were spent at all.
> 
> This means that every activate coinbase transaction has a unique hash
> and all new coinbases will be unique.
> 
> This means that all future transactions will have different txids.
> 
> There might not be an explicit rule that says that txids have to be
> unique, but barring a break of the hash function, they rules do
> guarantee it.


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