"Double-Spending" is an attack or failure which results in the same digital moneys being spent twice or more.

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Can someone double spend long after the block chain is extended (not the fork situation)? [on hold]

I am having this doubt, because every user, say Alice, has the digest of transactions from which it received the BTC (If Alice received 10BTC from Charlie, 5 from David). Now, it is not necessary that ...
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2answers
33 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 ...
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3answers
345 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 ...
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1answer
62 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?
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2answers
108 views

How does ShapeShift operate on 0-1 confirmations

ShapeShift can exchange user's crypto currency almost instantly. They state that most transactions don't require any confirmations: Small deposits are processed with zero confirmations. Larger ...
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2answers
118 views

Blockchain for internet-of-things or is there any mining algorithm that can be utilized in low-computational power devices preserving security?

Recently IBM and Microsoft showed their interest (IBM post, Microsoft post) in utilization of blockchain for internet of things development. Let's assume that in close future the blockchain technique ...
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1answer
133 views

What happens if a miner confirms their own double spend?

Suppose an attacker makes a double-spend and controls the mining pool that happens to find the good which confirms the transactions. What happens? I suppose the network hopes that a vigilante sees ...
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3answers
77 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 ...
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1answer
54 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
56 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
187 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
96 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
68 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
185 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
145 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
120 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
234 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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44 views

How can I fix a low miner fee due to errors?

I made a transaction a while back not thinking at the time give a very low miners fee (1 satoshi) and it's been a while since I sent it and it's still not confirmed and I started looking around. I ...
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2answers
160 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
92 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 ...
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2answers
150 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
155 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
27 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 ...
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2answers
68 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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14 views

Are transactions verified/checked also by full nodes, or only by miners? [duplicate]

Suppose I create an illegal transaction. Of course the default client won't create or sign such a tx to begin with, but for argument's sake let's say I rigged my software (built a modified version). ...
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2answers
53 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
149 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
40 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
52 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
621 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 ...
6
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1answer
512 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
59 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
156 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 ...
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135 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
59 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
151 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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35 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
133 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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117 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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4answers
269 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
99 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
626 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
88 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
33 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
115 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 ...
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1answer
2k 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
132 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
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1answer
1k 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 ...
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1answer
486 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 ...
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104 views

Disappearing transactions- a double spend attack?

A particular transaction occurred but it's tx hash can no longer be found in the blockchain. How can that be explained?