Whether you are a newbie or a guru in the crypto world, you might have seen "Double spending" Probably during one of your online searches or through word of mouth. So,  simply say, double-spending is the process of making two payments with the same  currency or funds to mislead the recipient of those funds. 

However, digital information may get replicated by intelligent persons who understand  the Blockchain network and the computational power required to manipulate it. Physical  currencies do not have a similar problem because they are difficult to duplicate.  Therefore, the parties involved in a transaction can quickly verify the currency's  legitimacy and previous ownership. Of course, this does not apply to cases involving cash  transactions. 

Double-Spending was initially a problem with Bitcoin (the most widely used digital  currency or "cryptocurrency) because it is a decentralized currency without a central  authority to ensure that it is used once. However, Bitcoin uses a method called the  Blockchain, based on transaction logs, to verify the legitimacy of each transaction and  avoid double-counting. 

Double-Spending in Cryptocurrency 

All Bitcoin transactions, without exception, must be recorded on the Blockchain. This  technique eliminates double-counting and other forms of fraud by ensuring that the party  that spends the Bitcoins owns them. As more transactions are added to the Blockchain of  validated transactions, it grows over time. Unfortunately, Bitcoin transactions take a long  time to verify since the process entails a lot of number crunching and complex algorithms  that require a lot of computing power. Moreover, it is impossible to do so because of the  enormous amount of computer power needed to clone or falsify the Blockchain. 

Types of Double-Spending Attacks 

Blockchain has solved the double-spending problem, but there are some attempts to  abuse the Bitcoin protocol using race attacks, Finney attacks, and 51 percent attacks. 

1Race Attack: A race attack occurs when a hacker submits two transactions in rapid  succession, with only one being validated on the Blockchain. The idea is to use the  unconfirmed transaction to buy something and then invalidate it before it is verified.  (This can only be possible if the recipient or merchant agrees to an unconfirmed  transaction) 

2Finney Attack: Finney attacks are only available to miners. The miner converts a  transaction from one wallet to another into a block. Then they initiate a second  transaction with the first wallet and broadcast the pre-mined block, including the first  transaction. To work, you'll need to follow a particular procedure. Finney attacks, like  race attacks, are only viable if the recipient accepts an unconfirmed transaction. 

351 Percent Attacks: a 51 percent attack happens when a group or an individual  controls more than 50% of the network's hashing power. The hacker(s) can use this  control to perform a double-spend attack. However, on the Bitcoin system, this scenario  is highly improbable due to Bitcoin's massive hash rate. 

To a large extent, Bitcoin has been able to escape these attacks. Still, other  cryptocurrencies with lower hashing power have been double-spent because of 51%  attacks. Because 51% attacks are so costly to carry out, they've primarily targeted large  exchanges with significant holdings. However, to be profitable, the attackers must  successfully spend twice as much as the attack cost.  

Double-Spending Attacks: Should You Be Worried? 

The answer is: You should never be concerned about double-spending attacks as long as  you do not accept unconfirmed transactions. Transactions that haven't been confirmed  will be labeled "unconfirmed" in most wallets and exchanges. Furthermore, the safer the  transaction is, the longer you wait. The risk of a reversal is shallow when several blocks  are uploaded to the Bitcoin network before the block holding your transaction. The  suggested wait time varies depending on the amount transmitted and the Blockchain.  Confirmations for each block on the Bitcoin network happen every 10 minutes. Block  confirmation durations on specific Blockchain networks are substantially faster, ranging  from seconds to a few minutes. 

Finally, in the Blockchain community, double-spending attacks have been extensively  examined and discussed. As a result, you can accept Bitcoin payments with confidence  that the risk of a double-spending attack is low as long as you don't get unconfirmed  transactions. 

Conclusion (How to Prevent Double Spending) 

Having read the above article, the question is; how does Blockchain help Prevent Double spending on Cryptocurrency? 

The emergence of Blockchain technology has been revolutionary in many ways, one of  which is the solution to the problem of double-spending. It eliminates all obstacles to 

current technologies. When it comes to cryptocurrency, Blockchain takes care of it by  developing a confirmation mechanism and having a universal ledger that is distributed to  all network peers. Blockchain is the technology that underpins cryptocurrencies, and it  has characteristics that make it an unavoidable technology. On this platform, any  transaction or data exchange is time-stamped and archived in chronological order,  making it incredibly simple to keep track of data. Nodes verify every transaction before  being recorded in a universal ledger. A transaction's block is added to this ledger every  10 minutes, and each node on the network receives a copy. 

Consider the case of someone who performs a cryptocurrency transaction and then  attempts to spend it again. The user would be unable to do so since. Once it begins, the  transaction is placed in the pool of unconfirmed transactions; because the miners only  validate and verify the initial transaction in Blockchain. However, the other transaction,  or a second transaction similar to it, does not receive enough confirmation since the  miners have discovered it is invalid. 

What if there is a situation where both transactions happen simultaneously, you might be  thinking? If transactions with the highest number of miner confirmations are added to the  Blockchain, the others will be deleted. It is, however, recommended that merchants wait  for at least six confirmations so that when a transaction is added to the Blockchain, the  six other blocks would be placed on it. Each transaction and block is linked  mathematically to the one before it. Once a transaction is recorded on the DLT or  Blockchain, it is difficult to change or amend it, making it secure.  

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