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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1answer
105 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 ...
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1answer
189 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 ...
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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 ...
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2answers
396 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 ...
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1answer
212 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 ...
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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?
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0answers
181 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?
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1answer
709 views

How does CryptoNote prevent a 51% attack and double-spending?

How does CryptoNote prevent a 51% attack and double-spending? I’m interested to know what is the mechanism that protects CryptoNote coins from 51% and double-spending attacks.
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1answer
946 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 ...
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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 ...
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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 ...
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 ...
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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?
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2answers
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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 ...
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2answers
145 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 ...
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2answers
205 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 ...
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2answers
654 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 ...
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1answer
104 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 ?
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1answer
102 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 ...
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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 ...
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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 ...
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1answer
115 views

Can a double spend attack be obfuscated by mimicking the transactions seen before the fork?

An attacker controls the majority of the hashing power and wants to double spend without arousing suspicion. If they mirror the public chain's activity while generating the private fork and the fork ...
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3answers
369 views

How is over-spending one block apart prevented?

So, let's say you have a wallet with 20BTC, and you have a flow like so: You send 15BTC to A in block 1 You send 15BTC to B in block 2 What happens if at block 1 there are two chains across miners. ...
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0answers
252 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 ...
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1answer
114 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 ...
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4answers
251 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 ...
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1answer
190 views

Which clients offer a way to replace unconfirmed transactions?

On this site, we see a lot of questions from people who have sent a transaction which isn't being confirmed, often because they have neglected to include an adequate fee. The Satoshi client doesn't ...
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1answer
306 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 ...
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0answers
309 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 ...
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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 ...
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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 ...
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1answer
120 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 ...
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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 ...
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1answer
105 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)? ...
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1answer
76 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 ...
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1answer
297 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....
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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 ...
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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 ...
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 ...
2
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1answer
604 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-...
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1answer
481 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,...
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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 ...
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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 ...
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 ...
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2answers
388 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
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1answer
216 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
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1answer
204 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?
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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?
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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 ...
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1answer
131 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 ...