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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8
votes
4answers
1k 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 ...
8
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2answers
921 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 ...
1
vote
2answers
384 views

Using Transaction with multiple outputs

Since the output can be spend only once, I am confused by transactions containing multiple recipients. For example, if Alice transfers 5 BTC to Bob and 5 BTC to David in the same transactions. In the ...
5
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2answers
268 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
386 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?
1
vote
3answers
528 views

What happens if a TX was a double spend?

What happens if the 'High' risk option (one confirmation) was chosen and then the TX turns out to be a double spend in the end? Would the value deposited be revoked? Would the user be notified somehow?...
0
votes
1answer
110 views

How do you inspect a transaction?

How do you inspect a bitcoin transaction to avoid getting scammed by a double spender? I'm buying bitcoins in cash and the seller said I could inspect a transaction instead of waiting 6 blocks. Is ...
0
votes
1answer
193 views

How to detect a race attack and re-spend the already-spent outputs?

My service automatically accepts, processes and sends payments to its users. It connects to bitcoind through its JSON-RPC API and makes use of the raw transactions interface. What is going to happen ...
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 ...
0
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2answers
1k views

How to recover from a double spending attack?

I found myself incapable of answering what would happen in this case, so here it is: A hacker (Mr Hacker) spends UTXO_1 and UTXO_2 in TX_1, depositing the monetary value of all TX_1's outputs into a ...
3
votes
1answer
282 views

JSON-RPC to detect double-spent TXs

How can I be positive that one of the incoming payments to my bitcoin-core was double-spent after it was confirmed once by the network, through the JSON-RPC interface? Related questions: How do I ...
2
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3answers
1k views

What's the easiest way to someone to double-spend 0-confirmation transactions?

I heard there is a desktop app today that 'easily double spends 0-conf tx'. Which is it? Is anyone working on a mobile version of this app?
0
votes
1answer
122 views

Could this stop double-spending?

Let's say you have a 15 second block time, and after your first transaction, your wallet's send button is frozen, and you have to wait for 2.5 minutes before you can send another transaction. Would ...
1
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0answers
182 views

Why are double-spends bad? [duplicate]

In the answer to this question it is stated the bitcoind filters doublespends. What is the reasoning behind this?
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 ...
1
vote
1answer
107 views

Curious about a network-based double-spending attack

In their paper Two Bitcoins at the Price of One? Double-Spending Attacks on Fast Payments in Bitcoin, Karame and Androulaki outline a particular race-attack that involves the slight control over a ...
1
vote
1answer
1k views

Warning about possible double spend at blockchain.info

What does this blockchain.info alert mean? Warning! this bitcoin address contains transactions which may be double spends. You should be extremely careful when trusting any transactions to or from ...
7
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3answers
191 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?
1
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2answers
195 views

How much hashpower is needed to double-spend? Is >50% a minimum?

How much hashpower is needed to double-spend coins? Some worry only about one entity getting over 50% of the hashpower, while others are complaining (at the time of writing) about an entity having ...
2
votes
2answers
39 views

Can too big hosted mining service be mitigated by allowing customers to choose mining pool?

Let's say a company is hosting mining hardware, either hosting customers' hardware or renting out the hashes produced by hardware owned by the company, or both. So the company is physically ...
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 ...
2
votes
2answers
724 views

Can Bitcoin scripting be used for double spending attacks?

A standard Bitcoin transaction deposits coins into an address and then, using Bitcoin's scripting language, states that whoever wants to spend this output must be in possess of the private key ...
1
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2answers
211 views

Can someone explain double spending to me?

I am restoring a backup of my Bitcoin Core wallet on a new PC. I downloaded the complete bootstrap.dat and placed it in ~/.bitcoin. I thought using the bootstrap would make things faster, but ...
2
votes
1answer
124 views

Double spending race attack first transaction

In tackling double spending, does the protocol enforces that only the first transaction (and by first i mean the first transaction to be send to the network) is considered as valid ?
1
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0answers
266 views

How big is the chance of double spending for 0, 1, 2, 3, 4, 5 and 6 confirmations?

I'm messing around with bitcoins a bit, and I'm now looking at the confirmations. In several places I read that 6 is the "normal" figure of confirmations needed to say a transactions has actually and ...
1
vote
1answer
329 views

Double spend attempts examples on testnet?

Where can I find some double spend attempts examples on testnet? Can anyone refer me some TXIDs with double spends on testnet? EDIT: I need some example in which an outpoint was intended to be used ...
0
votes
1answer
123 views

Double spend in transaction with multiple inputs

Lets assume we have transaction with 2 inputs, each worth 1 bitcoin, and we send these 2 bitcoins to one address. What happens if there is successful double spend attack on bitcoins in our first ...
2
votes
4answers
255 views

How much money is a double spend worth?

I keep hearing people say that 0 confirmations are safe at small dollar amounts because it would take more money to do a double spend hack. At what value does it start to become unsafe to trust a 0 ...
2
votes
1answer
332 views

How are Bitcoin ATMs secured against double-spends?

Some bitcoin ATMs allow the exchange from bitcoins to paper money. Since waiting in front of an ATM for a confirmation is not feasible, they must defend themselves in another way against double-spends....
3
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0answers
318 views

How to ignore balance check to cancel unconfirmed transaction (double spending)

I need to cancel a transaction that was sent without fee (using Blockchain.info). It is currently "Unconfirmed". The only way I have found is to do a double spend of the whole wallet, specifying a ...
2
votes
1answer
109 views

How strong is the bitcoin network?

Let's say an organization decides to attack bitcoin by launching a 50% attack. Can someone estimate how big the effort is? How expensive would such an attack be from scratch (buying enough ASICs)? ...
1
vote
1answer
80 views

Inbound connection merchant risk

I was recently looking at the safest way to set up an online bitcoin service. When looking for security concerns I ran across this post on stackexchange What are the risks of running an online store ...
2
votes
1answer
614 views

How often do double spends happen successfully?

Judging from this list, not very often: https://blockchain.info/double-spends Why is this the case? I would have guessed they would have been more frequent. Is it OK to always accept (small-to-...
5
votes
1answer
264 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 ...
40
votes
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 ...
1
vote
1answer
3k views

Sending from Bitcoin-Qt to Coinbase

I had the idea to move all of my existing bitcoins (10 BTC) from Bitcoin-Qt/paper wallet to Coinbase. I had imported the paper wallet to Bitcoin-Qt and the balance there was 10 BTC total. For some ...
6
votes
2answers
171 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 ...
2
votes
1answer
511 views

Is it possible to execute a double-spending attack in Ripple during a network split?

From the spec (emphasis added): Under a net split, a ledger may be closed by the minority of network, this ledger may be discarded in the future. Does this mean it would be possible to spend twice,...
23
votes
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 ...
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 ...
1
vote
2answers
389 views

Can double-spends be automated by malicious custom bitcoin clients? [duplicate]

Say a malicious mobile bitcoin client is created, programmed to quickly send two or more double-send transactions whenever a payment is made. Is this an attack vector we should be concerned of? ...
2
votes
1answer
221 views

Can Ripple Unique Node Lists (of validators) be weighted?

My understanding is that in order to limit / remove the risk of collusion in the Ripple system the consensus mechanism relies on local Unique Node Lists (UNLs) specific to each node in the network (...
2
votes
1answer
205 views

Is there a risk of double-spending when making a face-to-face transaction?

When exchanging funds or services face-to-face, is there a risk of a double-spending attack? If there is, how could it be technically done?
3
votes
1answer
132 views

How is it possible to detect system wide segmentation?

In this post, MoonShadow says it's easy to detect system wide segmentation. Yet a system wide segmentation is fairly easy to detect, the current client just doesn't do it. If code implementing my ...
11
votes
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
votes
2answers
606 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 ...
3
votes
1answer
289 views

Double spending from “green addresses” & mitigation

Suppose a user pays for a service (service1) using a "green address" (0 confirmations required) and service1 needs to immediately respend it using it's own green address How many blocks should the ...
1
vote
1answer
241 views

In a given contract, should the “LockTime” timestamp include an extra hour for confirmations to prevent a double spend?

Anytime a transaction has a timestamp attached to it, and there are signed but not submitted transactions at play, shouldn't the holder of the non-submitted tx have to take into account the ...
1
vote
2answers
209 views

Without being continuously connected to the network, how can I protect from Double Spend attacks?

I'm a vendor who is interested in protecting myself from double spend attacks. What software, configuration, connectivity, or timeout is required to mitigate this risk? Namely, how would I protect ...
4
votes
1answer
307 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 ...