[Bitcoin-ml] What i would like to see in the next HF + timeline

[Amaury Séchet]

2017-08-29 16:55 GMT+02:00 Tom Zander via bitcoin-ml <
bitcoin-ml at lists.linuxfoundation.org>:

> On Saturday, 26 August 2017 14:31:07 CEST Amaury Séchet via bitcoin-ml
> wrote:
> > Validation would go as follow:
> >
> > newUTXO = utxo.add(block.getAllOutputs());
> > foreach (i; block.GetAllInput()) {
> >     if (!newUtxo.spend(i)) {
> >         // Error !
> >     }
> > }
> >
> > utxo = newUTXO;
>
> This will fail in the case of these two transactions are included in a
> block.
> a) a TX that spends the last output of txid1
> b) a new TX that also hashes to txid1
>
> I can think of a simple 3-transaction loop that is capable of creating a
> duplicate transaction-id. (and, yes, this is legal even wrt to bip 30).
>
> This unfortunately kills the optimization you are thinking about.
>
>
I'm unclear how you can create two transaction that have the same hash.
There are some existing ones in the blockchain but they all have been made
unspendable.
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