Questions tagged [doublespend]

This tag should be used for questions related to double spending. Double spends are when a money is spent more than one time. This is considered a form of fraud.

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54
votes
7answers
44k views

Can bitcoins be counterfeited?

Traditional currencies have anti-counterfeiting features designed to make them hard to copy, but despite this attempt counterfeit money is a real threat. Since bitcoins are digital, it's trivial to ...
40
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2answers
5k views

How does Ripple solve the double-spend problem?

How does the Ripple system solve the double-spend problem? Does it also use some block-chain-like entity that officially dictates which transactions are confirmed and which are not, or does it use ...
32
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2answers
14k views

What is a Finney attack?

What is a Finney attack? Extra points for explaining its purpose, the prerequisites for it to be possible, how the attack can be performed and the origin of the name "Finney attack".
28
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5answers
5k views

Has there ever been a successful double spend attack on the Bitcoin network? If not, is it really necessary to wait for confirmations?

There is a lot of concern about waiting for confirmations to avoid a double spend attack, but has there ever actually been a double spend attack? It seems to be that there are two types of double ...
25
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3answers
37k views

What is a double spend?

What is a double spend? As someone who uses Bitcoin, what do I need to know about how the Bitcoin system prevents double spends? Are there still circumstances where they can occur?
22
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2answers
5k views

What are the pros and cons of Ripple's consensus as compared with Bitcoin's proof-of-work?

One of the major differences between Bitcoin and Ripple is how they process transactions. I can think of three ways in which Ripple's "consensus" scheme is superior to Bitcoin's proof-of-work: Less ...
21
votes
1answer
3k views

What does the Bitcoin client do when it receives conflicting transactions?

I've been assuming that the second transaction will simply be discarded as invalid, while the first waits at 0/unconfirmed until it actually gets into a block (requiring a "-rescan" or similar if the ...
17
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3answers
4k views

Are there alternatives for proof of work?

Bitcoin uses proof of work to secure the network, Ripple uses a global consensus system and PPCoin uses proof of stake. Are there any known alternatives to the above methods?
16
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2answers
6k views

How do I detect a double-spend?

As a vendor, how do you detect a double-spend? I'm happy to tell end-users that I'm proceeding with a transaction on 0 confirms, simply assuming everything is fine. I'm selling physical goods and so I ...
15
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1answer
978 views

Would a reduced block generation time make the Finney attack more difficult?

Related Question: What can be done to mitigate the risk of a Finney attack? The Finney attack is a form of double-spending attack where the attacker pre-mines a block containing a conflicting ...
14
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2answers
1k views

Does any pool accept higher-fee transactions of a double spend, instead of the earlier one?

Some pools use a modified bitcoind that uses different rules for choosing the transactions to include in a block. Are there any pools that knowing one transaction to be included in a block would ...
13
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2answers
2k views

How to minimize risk when accepting zero confirmation payments?

I'm trying to setup a way of accepting Bitcoin payments in real life situations, where waiting for confirmations is typically not an option. I understand this is never 100% risk free (especially with ...
11
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2answers
1k views

Double spend attack by sending higher fee transaction directly to the pools possible?

The standard client prioritizes TXs by the time of receipt, e.g. a conflicting transaction will not be relayed. This is not enforced by the network, though. Is there anything that would prevent this ...
11
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2answers
587 views

In a double spend attempt, how is the valid transaction chosen?

Suppose I publish the private key of an address that contains 1 bitcoin. If two people try to transfer this bitcoin to another address before a new block is found, who gets it? How is this decision ...
11
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2answers
2k views

Bitcoin without mining

Several months ago I've stumbled an interesting question about the Ripple system: How does Ripple solve the double-spend problem? Specifically about how double-spending is solved in Ripple. As you ...
10
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2answers
2k views

What is the Ripple equivalent of the “51% attack?”

In Bitcoin, if a participant gains control of more than 50% of the hash power, they can execute a double-spending attack. The "attack" could come from within, say if the existing powerful miners ...
9
votes
1answer
2k views

How does BitCoin prevent fraud during confirmation period?

I'm trying my best to understand how bitcoin works and while I've grasped the basics, there's a lingering question: What's to stop me from spending my bitcoin multiple times during a confirmation ...
9
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2answers
2k views

Could any standard fee transaction be double spent by using a higher fee?

I realize that if somebody makes a transaction without any fees and there have not yet been any confirmations, then the transaction could be double spent by just spending the same inputs to a ...
9
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2answers
349 views

Is there a service that alerts about attempted double spends for merchants accepting 0-confirmation transactions?

I often come across merchants accepting payment in bitcoin, who require several confirmations on transactions, but where the probability of a successful double spend doesn't justify the waiting time ...
8
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3answers
4k views

How do miners detect double-spending?

Assuming I spent 1BTC, then waited a few months and then spent it again. How is this detected? Do the miners go through the entire blockchain to assure the coin was never spent before?
8
votes
3answers
4k views

What is the best way to recover from an accidental double-spend?

Came across an issue where I was given the message: "Error: The transaction was rejected. This might happen if some of the coins in your wallet were already spent, such as if you used a copy of ...
8
votes
2answers
842 views

How does blockchain.info detect double spends?

http://blockchain.info/tx-index/242749/36080ed09eeb0fd66ad5dc8a909a49e364f55ff860c12327c2ff9fbe4a9dde77 Warning! this transaction is a double spend. You should be extremely careful when trusting ...
8
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3answers
761 views

Why is Poisson instead of Negative Binomial used for computing attacker's potential progress?

In chapter 11 of the Satoshi's paper it is claimed that: The recipient waits until the transaction has been added to a block and z blocks have been linked after it. He doesn't know the exact ...
8
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1answer
66 views

Merchant tool that will dynamically adjust the # of required confirmations based on network hashrate data

Satoshi built Bitcoin to be a decentralized network. Some of the original recommendations (such as waiting for 6 confirmations) relied on statistics that related to level of decentralization. https://...
8
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4answers
954 views

How do people actually try double-spends?

I've occasionally seen people online claiming they were victims of a double-spend because they handed over something of value in exchange for a bitcoin payment with no confirmations. Although I ...
7
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7answers
2k views

Is performing a 51% attack / double spend on Bitcoin illegal?

Suppose I had an ultra large ASIC from the future, and could perform a double spend on the core Bitcoin network. At this point in Bitcoin's development, it is no longer a game - there's real money ...
7
votes
2answers
573 views

Possible to create a double spend attack by replacing a Tx in the merkle tree?

This question on crypto.SE describes how preimage attacks are avoided in the Bitcoin network. For a second preimage attack: hash(x) = hash(y) implies hash(hash(x)) = hash(hash(y)) So it ...
7
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3answers
188 views

Does using Ripple to accept Bitcoin reduce risk of Bitcoin fraud?

Does Ripple reduce the risk of double-spending, or other types of issues that may crop up when using Bitcoin natively?
7
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4answers
235 views

Do no-fee transaction represent a greater risk if the product is delivered instantly?

Let's say I want to accept payments instantly on a site for digital downloads. So I publish an address and wait for the unconfirmed transaction, I see the transaction and release the digital download....
7
votes
3answers
2k views

How does Open Transactions solve the double spend problem?

OT is based on digital cash. From the article: To tackle the double spending problem, the payee has to verify the coin with the bank at the point of sale in each of the transactions. This ...
7
votes
1answer
618 views

Speeding up confirmation by double-spending a transaction stuck in mempool

In the context of no-fee transactions that can take a long time to get their first confirmation, is it possible to use raw transactions and double-spend the original transaction by broadcasting ...
6
votes
3answers
677 views

Why doesn't bitcoin place additional constraints on competing block chain forks, other than length of chain? (e.g., time and confirmation count)

In Bitcoin's proof-of-work system, consensus on which chain of blocks should be considered the "true" block chain is based only(?) on which chain is longer. Accordingly, to quote a nicely written ...
6
votes
2answers
7k views

How is a Transaction Output Marked as Spent?

The Bitcoin developer guide states that each output of a particular transaction can only be used as an input once in the block chain. Any subsequent reference is a forbidden double spend—an ...
6
votes
2answers
1k views

Double Spending - Does each node maintain a list of unspent transaction references?

My Understanding Of How Bitcoin Prevents Double Spending Each transaction contains references to the input transactions and ever node has to verify all transactions from time immemorial to ensure ...
6
votes
2answers
161 views

What precautions to take when working with only one or two confirmations?

I am providing a service that accepts Bitcoin. In order to speed things up a bit, I am planning to reduce the number of confirmations I require before I consider the money to have arrived. I have ...
6
votes
1answer
1k views

What does a double spend look like?

What does a double spend look like? Can anyone link to an example on blockchain.info? Will invalid half of the double spend simply remain at 0-confirmations, or might it ever reach 1 or 2? Will the ...
5
votes
1answer
3k views

Understanding a Bitcoin Double Spending Transaction by Performing one on yourself

Everyone talks about preventing a double spend transaction, but how does one do one to yourself in order to better understand the steps involved by the attacker? What is required to do a double spend?...
5
votes
2answers
607 views

How to perform a double spend attack in websites that accept transactions with 0 confirmations?

To perform a Finney attack or a 51% attack I need to have lots of computational power, but in this case (a website that accepts transactions with 0 confirmations) it seems to me that I only need to ...
5
votes
1answer
359 views

What exactly happens when a node detects a double spend?

Does the node drop both transactions? Does the node choose which one to keep? What exactly happens? Will both transactions be rejected by the network or will one of them be eventually accepted?
5
votes
2answers
195 views

Possible error in the white paper Calculations section?

Section 11 presents calculations of the probability of double spending, P(z, q), given an attacker relative hash rate q and a block count z. P(z, q) can only be understood by knowing exactly what z ...
5
votes
2answers
237 views

Double spend transactions flag the node as “bad”?

I'm playing with raw transactions. It's easy to send two signed valid transactions at the same time from the same output to different addresses (making a double-spend attack). My doubt is: if I make ...
5
votes
1answer
2k views

What to do about a “stuck” transaction?

I started the standard client with --rescan instead of -rescan after switching wallets and before synchronizing with the latest blockchain, and made an going transaction. This transaction got "stuck",...
5
votes
2answers
879 views

0/confirmation race attack double spend transactions

I am developing a point of sale bitcoin app, which should accept "fast" transactions (~30 sec for merchant to accept). I researched double spending questions here already, but it is still unclear to ...
5
votes
1answer
3k views

Can someone explain this double spend on blockchain.info?

I'm confused by double-spend linked below, in which both transactions ended up in blocks mined by different miners. Specifically, I'm wondering if there's any way to tell what exactly happened based ...
5
votes
1answer
232 views

What can happen if/when a node is surrounded by rogue nodes?

If a node (V) accepts incoming connections, is he vulnerable to becoming completely surrounded by corrupted nodes? Would an attacker be able to control which transactions are relayed to V and which ...
5
votes
1answer
2k views

How to clear invalid transactions from one's wallet?

I've recently been testing double-spend attacks against myself using a couple wallets, and the standard client does not appear to clear conflicting transactions from its transaction list, even if the ...
5
votes
2answers
744 views

Double Spending before confirmation [duplicate]

What's to prevent someone from using bitcoin at a store like subway and double spending to buy the sandwich before a confirmation is made? Since subway obviously isn't going to wait for a ...
4
votes
2answers
2k views

It's possible to spend a BTC without fee to forge a payment?

I would like to know if it is possible to make a transaction without fee (probably this transaction will never be confirmed) and some time later to take this money back and spend in another ...
4
votes
1answer
304 views

How to force bitcoind to include a specific transaction as an input of another transaction?

I would want to force bitcoind to include a specific transaction as an input of another transaction. This is so as to prevent people front wanting to launch a double-spend attack on the website. The ...
4
votes
2answers
3k views

Broadcast a signed transaction

I sent money from 4 inputs to 2 outputs, one of which I don't control. The transaction's fee is too small (didn't change my settings and the transaction fees got a lot higher, recently) and will not ...