[Bitcoin-development] Possible attack: Keeping unconfirmed transactions

Toshi Morita toshi at peernova.com
Fri Jun 6 22:11:28 UTC 2014


>From what I know, Alice does not know to which node Bob will broadcast the
transaction. Therefore, Alice cannot intercept the transaction and prevent
the rest of the network from seeing it.

Toshi



On Fri, Jun 6, 2014 at 3:02 PM, Raúl Martínez <rme at i-rme.es> wrote:

> I dont know if this attack is even possible, it came to my mind and I will
> try to explain it as good as possible.
>
> Some transacions keep unconfirmed forever and finally they are purged by
> Bitcoin nodes, mostly due to the lack of fees.
>
>
> Example:
> ---------
>
> Alice is selling a pizza to Bob, Bob is now making the payment with
> Bitcoin.
> The main goal of this attack is to store a unconfirmed transaction send by
> Bob for a few days (it will not be included in the blockchain because it
> has no fee or due to other reason), Bob might resend the payment or might
> just cancel the deal with Alice.
>
> Bob forgets about that failed trade but a couple of days later, Alice, who
> has stored the signed transacion, relays the transaction to the network (or
> mines it directly with his own hashpower).
> Bob does not know what is happening, he believed that that transaction was
> "canceled forever", he even does not remember the failed pizza deal.
>
> Alice has now the bitcoins and Bob does not know what happened with his
> money.
>
> ---------
>
> This might also work with the Payment Protocol because when using it Bob
> does not relay the transaction to the network, its Alices job to do it,
> Alice stores it and tells Bob to resend the payment, Bob creates another
> transaction (If has the same inputs as the first TX this does not work)
> (this one is relayed by Alice to the network).
>
> Alice comes back a couple of days later and mines with his hashrate the
> first transaction (the one she didnt relayed to the network).
>
> Alice now has two payments, Bob does not know what happened.
>
>
> -----------
>
> I hope that I explained well this possible attack, I dont know if there is
> already a fix for this problem or if it is simply impossible to execute
> this kind of attack.
>
> Thanks for your time.
>
>
>
>
>
>
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