Why some platforms need X confirmations?

[javierfjavier]

Well, first of all hi to everybody, i'm a newbie in this cryptocurrency thing, so a lot of doubts are in my mind these days.
I have this question, looking here for the answer I didn't found yet, basically the subject says it all.

If bitcoin transactions are irreversible, why some platforms (online wallets, exchanges, etc) need X confirmations to "validate" a transaction?

[Snorek]

Well, first of all hi to everybody, i'm a newbie in this cryptocurrency thing, so a lot of doubts are in my mind these days.
I have this question, looking here for the answer I didn't found yet, basically the subject says it all.

If bitcoin transactions are irreversible, why some platforms (online wallets, exchanges, etc) need X confirmations to "validate" a transaction?

You answered yourself. Exactly due to fact that bitcoin transaction are irreversible it is wise to wait for at least 1 confirmation of the network.
Unless there is 1 (or more confirmations) there is a risk of 'double spending' of bitcoin.

[unent]

There is always a risk that the blockchain might fork, which means there will be two blockchains for a short duration until the miners decide which is the best chain. Coins on the blockchain that gets discarded can be invalid on the other blockchain. After six confirmations it's safe to assume there has been no fork, and that your coins are safe. Most exchanges wait for six confirmations to protect themselves from the possibility of a fork.

[EternalWingsofGod]

If bitcoin transactions are irreversible, why some platforms (online wallets, exchanges, etc) need X confirmations to "validate" a transaction?

To prevent a double spending attack, at times the network can take more than 10 minutes to validate the transaction and if a block is not found quickly then in order to ensure that their is no mistake between two different communicating transactions to different addresses being propograted exchanges use 1 to 3 confirms before confirming the amounts.

[ranochigo]

Well, first of all hi to everybody, i'm a newbie in this cryptocurrency thing, so a lot of doubts are in my mind these days.
I have this question, looking here for the answer I didn't found yet, basically the subject says it all.

If bitcoin transactions are irreversible, why some platforms (online wallets, exchanges, etc) need X confirmations to "validate" a transaction?

You answered yourself. Exactly due to fact that bitcoin transaction are irreversible it is wise to wait for at least 1 confirmation of the network.
Unless there is 1 (or more confirmations) there is a risk of 'double spending' of bitcoin.

Double spending risk always exist unless the transaction is confirmed and included in a block before the last Bitcoin checkpoint. Without any confirmation, the risk of race attack is very high. After 6+ confirmation, without significant hashrates, the risk of double spending is reduced. Unless there is a major block reorg which is quite impossible unless your client is bugged.

51% hashrate is a number which miners need for a double spend attack to succeed with 100% chances. The lower the percentage, the lower the chances. Services that require significant amount of confirmations probably do not want to lose their coins at any case for example, exchanges. For normal brick and motar stores, 1 confirmation or even 0 confirmation is enough for the risk to be reduced. That is if precautions are taken.

[odolvlobo]

If bitcoin transactions are irreversible, why some platforms (online wallets, exchanges, etc) need X confirmations to "validate" a transaction?

Saying that "a bitcoin transaction is irreversible" is a simplification. A transaction is not reversible in ordinary circumstances, but...

Without getting into too much technical detail, a transaction can possibly be canceled before the first confirmation by simultaneously making another transaction that spends the same bitcoins (so-called "double-spending"). If the competing double-spend transaction is the one that is added to a block, then the original is canceled (and thus reversed).

It is possible for a block in the block chain to be replaced by another block. There is about a 1.5% chance of that happening to a newly added block. So, even if the original transaction is added to a block in the block chain, there is a small chance that the block is replaced by a diiferent block that may contain the competing double-spend transaction, which would cancel the original transaction.

The permanence of a block depends on the number of blocks that follow it, so waiting for a certain number of blocks (typically 1, 3, or 6) reduces the chances of becoming the victim of a double-spend.

[1990BEARS]

to prevent double spending/fraud transactions

[yurinov]

Well, first of all hi to everybody, i'm a newbie in this cryptocurrency thing, so a lot of doubts are in my mind these days.
I have this question, looking here for the answer I didn't found yet, basically the subject says it all.

If bitcoin transactions are irreversible, why some platforms (online wallets, exchanges, etc) need X confirmations to "validate" a transaction?

to make sure all fee is paid and so transaction confirm by network. If does not confirm money is useless and go back to sender!!

[ranochigo]

Well, first of all hi to everybody, i'm a newbie in this cryptocurrency thing, so a lot of doubts are in my mind these days.
I have this question, looking here for the answer I didn't found yet, basically the subject says it all.

If bitcoin transactions are irreversible, why some platforms (online wallets, exchanges, etc) need X confirmations to "validate" a transaction?

to make sure all fee is paid and so transaction confirm by network. If does not confirm money is useless and go back to sender!!

Transactions without fees can get included into a block too. A block typically have 50kb reserved for that. For a free transaction, you need to have the size below 1kb, all outputs above 0.01BTC and the priority must be high enough. If not enough fees is paid, the merchant can use CPFP and rebroadcast it continuously to reduce the possibility of a double spend.

[Amph]

it's a weakness of bitcoin sadly, to rpevent some strong attack like 51% 40% and 30% of hash rate, like the finney attack for example

it's a form of security, like bank use cvv for their credit card, or multiple password etc...

[dothebeats]

It is imposed so as to prevent double-spending attempts on the network and to 'validate' transactions happening within the network. Another thing is what one user already mentioned about forking.

[ATguy]

If bitcoin transactions are irreversible, why some platforms (online wallets, exchanges, etc) need X confirmations to "validate" a transaction?

As others said it is to counter the risks of possible double spend. But the risk is only if you deliver some instant service, and if you sending the goods physically or generally deliver non instant service then you dont need confirmations because you simply cancel the order once you detect double spend.

[Jeremycoin]

To avoid double spending, and usually online store just need 1 confirmation. Why 1? Because they don't want the customer to wait for another confirmations because it would take a longer time (1 is enough).

[artifical100]

business need protection from double spend, which are transaction that get sent back to sender if miner cannot confirm it.

[ranochigo]

It is imposed so as to prevent double-spending attempts on the network and to 'validate' transactions happening within the network. Another thing is what one user already mentioned about forking.

Transactions are validated as nodes relay it, Bitcoin nodes do not relay invalid transaction. It is only to prevent coins from being spent twice by recording it as a ledger. Before it is included in a block, it is not recorded in the blockchain.

[dothebeats]

It is imposed so as to prevent double-spending attempts on the network and to 'validate' transactions happening within the network. Another thing is what one user already mentioned about forking.

Transactions are validated as nodes relay it, Bitcoin nodes do not relay invalid transaction. It is only to prevent coins from being spent twice by recording it as a ledger. Before it is included in a block, it is not recorded in the blockchain.

I guess my understanding is somewhat crooked when it comes to validation of transactions within the network. Thanks for pointing me out on the right way. You got to learn new things--or correct your knowledge--everyday.

[enthus]

they do this so all transaction validated by miner on the network.  so they are valid.

[Kprawn]

This confirmation things sucks sometimes... A while ago, there were some "flash" sales going on, and I ordered something. The deals expired every 1 hour and then they replaced it

with another item. I scanned and paid within the hour, but the transaction did not go through due to "stress testing" going on for nearly 2 hours 20 minutes. {You remember those

times?} Well the site confirmed the sale, once 3 confirmations went through, but they made me pay the full amount, less 20%. I lost out on a less 50% discount. 

[thejaytiesto]

Well, first of all hi to everybody, i'm a newbie in this cryptocurrency thing, so a lot of doubts are in my mind these days.
I have this question, looking here for the answer I didn't found yet, basically the subject says it all.

If bitcoin transactions are irreversible, why some platforms (online wallets, exchanges, etc) need X confirmations to "validate" a transaction?

You answered yourself. Exactly due to fact that bitcoin transaction are irreversible it is wise to wait for at least 1 confirmation of the network.
Unless there is 1 (or more confirmations) there is a risk of 'double spending' of bitcoin.

Even with 0 confirmations the risks of double spend are insanely overblown. Unless you are paying a lot for something really important, then chances are you can be perfectly ok with 0 confirmations and sleep better at night, certainly better than credit card transactions.

[notlist3d]

Well, first of all hi to everybody, i'm a newbie in this cryptocurrency thing, so a lot of doubts are in my mind these days.
I have this question, looking here for the answer I didn't found yet, basically the subject says it all.

If bitcoin transactions are irreversible, why some platforms (online wallets, exchanges, etc) need X confirmations to "validate" a transaction?

You answered yourself. Exactly due to fact that bitcoin transaction are irreversible it is wise to wait for at least 1 confirmation of the network.
Unless there is 1 (or more confirmations) there is a risk of 'double spending' of bitcoin.

Even with 0 confirmations the risks of double spend are insanely overblown. Unless you are paying a lot for something really important, then chances are you can be perfectly ok with 0 confirmations and sleep better at night, certainly better than credit card transactions.

The risk is not zero though.   Double spends can happen so why not prevent them?

With waiting for a few confirmations you stop double spending, and assure you receive the BTC.  So I think it's worth it and we will people continue to wait.