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

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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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34 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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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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56 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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59 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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128 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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26 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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54 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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11 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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43 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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78 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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25 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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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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199 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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398 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
37 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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137 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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90 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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45 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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139 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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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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90 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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102 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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189 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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431 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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85 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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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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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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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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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 ...
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840 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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453 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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101 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?
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208 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 ...
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559 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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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 ...
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231 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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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? ...
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128 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 ...
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166 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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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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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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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 ...
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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 ...
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378 views

How does the Bitcoin client check for double spend?

When the Bitcoin client looks at the input of a transaction, it know the hash of the previous transaction from which the funds are coming, however then, how does it know that this output has not been ...
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132 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 ...
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133 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 ...
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141 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 ...
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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 ...
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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 ...