Topic: Has anybody ever successfully double spent? - page 2. (Read 3139 times)

Not to nitpick but dan typically applies to Japanese martial arts. Kung Fu uses a different term for black belt ranks.

I sp34ks interweb, anything-fu = comparison to a martial art, masters of martial arts have black belts of rank 1st dan, 2nd dan, 3rd dan etc...

I'm assuming that English isn't your first language?  I'm having difficulty understanding what you are trying to say in this comment.  Perhaps if you post it in your native language, I can decipher it a bit better?

Life is a gamble.  Every time we step out our front door, we are gambling and taking a chance that we might die.

All we can do is mitigate the risks to a tolerable level.

The four conditions that I place I accepting a transaction with 0 confirmations are sufficient for bringing the risks to my own personal tolerable level.

The increased reduction in risk by getting confirmations is negligible if those four conditions are already met.

You'd be gambling, Mr Hamilton here is 2nd Dan in Blockchainfu.

I see you like gambling...

Blockchain.info has a flag on one of my addresses accusing it of double spending. However, I think that is based on blockchain.info's flakey timestamping, registering an output several minutes before an input or something.

I have happily accepted transactions in excess of $5000 with 0 confirmations when it met the following conditions:

• I had reliable identifying information about the sender
• I was able to see that it was a standard transaction
• The transaction included a reasonable transaction fee
• I was able to determine to my satisfaction that there weren't any competing transactions with identifiable propagation

I had no concern at all.  Any merchant can do the same.

May be relevant - GHash.IO and double-spending against BetCoin Dice

+1.  We don't hear much of this idea and it is a great answer to complaints about block times.

Yes i agree. Double spend is a crime and crime never pays off.

If:

• You both were connected to different peers
• You created the transaction so that both wallets spent the same unspent output
• You could time it so that both of your wallets transmitted your transaction at the exact same time

Then each merchant would have a 50% chance of seeing the unconfirmed transaction at all.  In other words, each merchant would have a 50% chance of seeing a transaction with 0 confirmations that sent bitcoins to their address, and a 50% chance that they'd be sitting there waiting for you to pay them, because they don't see the transaction at all.

Eventually 1 of the transactions would be confirmed.  At that time, the competing transaction would cease to exist.  It would be dropped from the memory pools of all peers.  The transaction that did get confirmed would be seen by the merchant that the payment was made to with 1 confirmation.

So, if you got lucky and both merchants saw their own unconfirmed transaction, and if the merchant allowed you to leave with the merchandise while there were 0 confirmations, then you would have committed "shoplifting" (since you left with merchandise that you didn't pay for) and they would call the police and report the theft.  Then the police would review their security cameras, get a description of you from any witnesses, and the shop would be watching for you to return.  If the shop is accepting transactions with 0 confirmations, and they aren't completely stupid, then they will require that you provide identifying information (such as a government issued photo ID, or a "frequent customer" card issued by the shop) along with the purchase that will have been recorded with the transaction.  This identifying information will also be turned over to the police.

Additionally, any merchant that is willing to accept transactions with 0 confirmations really should be running custom software that will maintain connections to a very large number of peers.  This custom software should alert them if it received conflicting transactions from different peers.  This alert should occur within a second or so of you both sending your transactions.  As such, both merchants will immediately know that you are attempting a scam, and that they should not allow you to leave with the merchandise until they see at least 1 confirmation on the transaction.

Essentially, a transaction with 0 confirmations is a lot like a personal check.  If you have $20 in your bank account, and you and your wife in separate shops each write a check for $18, what will happen?  Assuming that the bank doesn't allow you to overdraw your account, one check will "bounce".  You'll have committed fraud, or theft, and the merchant can press charges in court if necessary. A merchant should treat a transaction with 0 confirmations with the same scrutiny that they treat a personal check.  Of course, since all transactions in bitcoin are completely public, the merchant has extra tools available to them to reduce their risk with bitcoin transactions that they don't have with personal checks (such as monitoring peers for conflicting transactions, and the ability to know for certain that the funds being spent actually exist).

What would happen if you and your wife had cloned wallets and visited two separate merchants who accepted bitcoin and made purchases using synchronized watches?

I think most wallets won't let you try , so would need a slightly modified version of a wallet that would allow you to broadcast a (non valid ) transaction that has already spent funds. 

double spant will cost so much money , no borning people will do this thing for bitcoin
but i think this will happen in altcoin

^^ This.  Very much this. ^^

A true double spend (where a previous transaction output is used as an input in two different transactions that are both permanently recorded in the blockchain) is impossible.  It never has happened. It never will happen.

However, people that don't understand the technical detais of how bitcoin works like to use the words "double spend" to describe a variety of scams that allow an attacker to fool their target into believing that they've received bitcoins that they never actually received.

So, if you are asking about a true double spend, then no, it hasn't ever happened.  It never will.

If you are asking about a scam where someone is tricked into believing that they've received bitcoins that they haven't due to the target's own misunderstanding about how bitcoin works, then yes.  That has happened many times.

I think in the old times yes. Blockchain actually has a list of all double spents that have occured till now.

If you are talking about 0 confirmation transactions then it's rather easy to double spend. Send a transaction with no fee, then roll back your transactions and send the same transaction with a higher fee so it gets included into the Blockchain first, rejecting the first transaction. This only applies to accepting 0 confirmation transactions though, you would need a lot of mining power to try and get transactions with one or more confirmation through.

It just so happened that my first transaction I sent with Bitcoin was with no fee and was stuck for 4-5 days trying to get into BTC-e with no confirmations and so had to do something. The first transaction was left in perpetual limbo as 0 confirmations so technically it wasn't a double spend.

Define "double spent", please. There are different definitions of this term and depending on what you are asking about the answer may be YES or NO.

i don't think anyone will tell this even if he has done it successfully
many people do this, or scam others with fake transactions