Topic: Double spent really not that much of an issue? (Read 1001 times)

Transactions propagate across the network in 2-3 seconds. Once that has happened, nodes will reject any subsequent attempt to double spend the same coins.  That is why for all practical purposes a bitcoin transaction is instant. There are clever ways to get around this, but none of them are easy or cheap.

Aside from the fact that you will find it extraordinarily difficult to double-spend your coins before the merchants have received your previous spends on the network (and therefore will reject your double-spend attempts), there's another problem you failed to take into account:

The next time you're in such a station, look up. Then smile and wave. Your (attempted) theft will be recorded on dozens of cameras. Not exactly the perfect crime you were hoping for.

There is always the problem, that you need the receiver to know your false transaction first, before any of the other transactions. If you do 1000 transactions with the same coin, how will you make sure the receiver knows only about the 1 transaction he is supposed to know about and not the remaining 999.

Archiving that would be very expensive. That's why it makes sense to wait on high value goods.

IIRC some bitcoin gambling website got hit huge by a double spend attack?

Yes. Every Bitcoin node, that already knows about your 1. Transaction would immediately recognize every other transaction as double spend.  So in order to do this you would have to make sure somehow, that the first shop knows about your first transaction, but every other shop doesn't. In order to make this possible, you would somehow need to separate each shop from the Bitcoin network and connect them to your Node only. That's hard, risky and very expensive. If all the shops use the same Payment provider, let's say BitPay, it's impossible.
 

I am not sure I agree "for small transactions it is non-issue". I think people are envisioning 200 people with the same coin in 200 starbucks and not 200 computers performing a dual DDoS of the blockchain with simultaneous transactions.  

If you can double spend thousands of small transactions simultaneously while doing a DDoS or DNS Man in the middle attack on the Blockchain this could be huge. As more online products take advantage of Bitcoin I could order 1000 different computer games simultaneously all with the same coin (DRM will use a blockchain / colorcoins/mastercoin concept to prevent piracy in the future). I could also make make 100 small conversions of same Bitcoin for different Litecoins in the future (Peer to peer crytpo to crypto currency exchanges will eventually be significant number of transactions).   There are hundreds of examples where a well timed low value high volume transaction can occur on line.

This is still an issue, not solved one, that means bitcoin payment is not reliable like bank, you have a chance to lose money using bitcoin.

oh wow, thanks, didnt know this "the network will reject an attempted double-spend", this is the first time i hear theres some feature in bitcoin that can do that, can you please tell me mow how it works? really, i hear it for the first time, i just read over and over again that double spent might be an issue and now you are telling me theres already in feature in BTC that can prevent double spent even before that "real check" takes places (confirmations).?

This has been addressed numerous times. For small transactions it is a non-issue. Even before a transaction is confirmed, the network will reject an attempted double-spend.

I have double spent coins unintentionally using qt when swapping old/new wallets around.  To do this intentionally to cheat someone out of a couple bucks would be a real pain, and time consuming.  Unless you script something or use a tool that I'm not aware of, it just wouldn't be worth it.

Aside from that, I suspect that by the time it's common for your local corner shop to accept Bitcoin, micro payments will be made through payment processors so that transactions can be instant and off-chain.

When paying for big ticket items like a car, you of course could opt to use your wallet to send the coins.  By the time you're done signing your paperwork, your transaction will be confirmed.

And sure if you buy a pc or a car. both your and the seller will wait that few minutes for example, probably, but its still not that much quick and confort as using cash, but its still ok.

But in that one case of mine (small amounts for "little" goods, payed quickly, not waiting for confirmation, many shop at your immidiate physical distance... i see that as an issue, im not sure if this was particulary adressed or not... what do you think about it, is there a REAL solution? (and no, real solution is really not waiting couple of minutes everytime i buy some stupid cheap product (bakerys roll a magazine etc.)


Also, is it possible to speed up the confirmation in the future...?

Hello
Is double spent really not that much of an issue? I heart people say so, that for small transaction (i mean in real life now, not over internet) as buying a coffee you dont have to wait for transaction confirmation, but when buying something more expensive it wont hurt you to wait few minutes (like buying a car or a pc etc.). I quite (but not fully) agree with this. But what for a situation, when bitcoin is widely used in real life and you are for example in a big station (air, port, train etc.) and you want to "use the system for your advantahe". So lets say you have only 0,005 BTC which you own (around 3 dolars) and you go to one shop to buy some magazine, you dont wait for confirmation and so doesnt the shop keeper, its a small ammount and everybody is an a hurry (its a train station...), but 5 seconds after this buying, you go right to the next shop, which stands just meters away from the previous one, and with that same ammount (of already spent, but not accounted/confirmed) ammount of 0,005 btc you go and buy a baker product (some pie), then few seconds after you go to anoter shop and buy some drink, then to another shop and buy some chips, and then another etc... Its takes you around 1-3 minutes (it can really be just 1 minute) and you have already quadruple spent your 0,005 BTC (4 time, 5 times etc.)...

I see that really as an issue if BTC get WIDE adoption... Am i missing something here?