Bitcoin Forum

I just thought about this today. Every time you are transacting with bitcoin, you will be told that you have to wait for bitcoin confirmation. This is common with bitcoin gambling sites. What I know is that bitcoin transactions are irreversible. Then why is it that you have to wait for the confirmation before initiating anything?

This is to prevent people from double spending those coins. There is a way to sort of 'charge back' BTC and waiting for this confirmation insures it is a valid transaction.

Person sends transaction to address with small fee and then sends another exact transaction to another address with a much higher fee so it gets confirmed first which will invalidate the original transaction allowing them to keep their coins. This is very, very difficult to do though but not impossible.

It is simple because of double spend,it is not common again but some people can still try the trick, you can't trust anybody

i think if we make payment for what we buy like for example we make invest in cloud mining, prepaid phone card, pay our bills, maybe its not need much of confirmation because there is a payment that only need 1-3 confirmation and then the order is complete.

we have to wait the confirmation is because our transaction will be seen on the network and the amount that we send can get transfer into the other wallet address. if you note, you can see when you make the sending amount, the message is waiting to be seen on network. it means, your transaction is need to be on the network list so the transferred amount is send.

Even though the possibility of a double spend is very low, some small rest of risk always exists.
That's why we are told to wait for confirmation.If however you have 100% trust to your other party, because you know him for many years and everything always went smooth and fine you don't need to wait of course.

I get your point. I never imagined if there could be a double spend in bitcoin transactions. But human beings are mysterious and they can do anything you cannot imagine.

Its because so that to prevent them from double spending their coins .its common and many people use some trick so trust no one . And if u wanna safe transaction u have to to be patience .kudoos :)

Hmm,
Does not seem that hard,

Have 2 PCs running side by side, with a copy of your BTC wallet on Each, opened and synced,
from the 1st PC send your BTC to an address you control, (pay the extra fee on this one or wait 50 seconds before sending on the 2nd PC.)
from the 2nd PC send the BTC to the guy you are doublespending to.

I believe that is about the gist of it, any extra steps , feel free to add.  ;)

 8)

Normally there is not real need to wait for a confirmation of bitcoin, especially with smaller payments.

Bigger payments may be a different game (say you are buying a car), but even then, a double spend is not easily done.

On the other hand, you will have the time to wait on confirmations with big payments due to the paperwork etc, just let it confirm while you are doing the boring stuff.

bitcoin transactions are only irreversible AFTER confirmation.
imagine it like:
writing a cheque. you can validate the cheque by calling the bank and checking the balance is available to spend and the person is who they say they are. but until the cheque is cleared by the cheque clearing house you dont yet have the funds to spend yourself and the funds can bounce.

writing a transaction. you can validate the transaction by checking the inputs and checking the balance is available to spend and the signature belongs to the inputs. but until the transaction is confirmed into a block you dont yet have the funds to spend yourself and the transaction can be rejected.

there are a few ways to write a transaction announcing you as the destination. making you see the unconfirmed transaction. but then write another transaction using the same original input funds to move the funds elsewhere and getting that transaction accepted into a block before the one you were hoping for. thus making the one you were hoping for get rejected.

so until the transaction you were hoping for is confirmed (irreversible) dont trust it.

double spends are actually easy.
(a)someone makes a tx to you, but have insufficient fee.

(b)someone makes a tx to themselves with a sufficient fee. and then a (c)third transaction prespending that transaction with a suffient fee to push transaction c through.
this is using features called RBF(replace by fee) and CPFP(child pays for parent)

so until the transaction you were hoping for is confirmed (irreversible) dont trust it. especially ones with insufficient fee

This is a very detailed insight and it has opened my eyes. Actually, someone can send you bitcoins and forward the transaction ref to you as prove of payment. This means that the tx ref only can not act as prove of payment until there are confirmations on the transaction. 

The sole purpose of confirmation on the transactions I learned here is that for a transaction to go through, you need to be confirmed to see if it really made through.  Miners will try to confirm it. It's like validating if the transactions are real and if they really did it. Double spending will be prevented if the wallet has indeed that kind of amount. Depending on the transaction made. For small amounts of transactions, I think 1 - 3 confirmations are okay, but for large amounts, not only that transaction fee is higher, but also the confirmations should be bigger. Patience is a virtue.

Thats a really confusing sentence, but it sounds like you are trying to say that transactions need a confirmation in order to be check for validity. Thats not true. Every full node (e.g. the bitcoin core wallet) can do this, with or without confirmation.


A miner cant tell how much bitcoin you have in your wallet.


Thats bullshit. Transaction fees have nothing to do with the amount of bitcoin you transfer. They depend on the size of the transaction in byte.

For bigger amount I think its the same. Once you see that there are confirmations already, I think its ok, meaning it is already being processed on the system.But of course, we are very cautious , since it is a bigger amount. :)

May I ask @shorena , the transaction size (in bytes) is directly proportional to the amount? tia

No, a single input has 148 (compressed pub key) or 180 (uncompressed pub key) byte. An input can be worth any (valid) amount of bitcoin. A transaction spends inputs and creates outputs (~34 bytes each).

After a transaction is broadcast to the Bitcoin network, it may be included in a block that is published to the network. When that happens it is said that the transaction has been mined at a depth of 1 block. With each subsequent block that is found, the number of blocks deep is increased by one. To be secure against double spending, a transaction should not be considered as confirmed until it is a certain number of blocks deep.

maybe you can get more information from this article. https://en.bitcoin.it/wiki/Confirmation (https://en.bitcoin.it/wiki/Confirmation)

we all know that one of the factors that affect the speed of delivery of bitcoin is the amount of the fee we include.
so the larger the fee it will be more easily split the bitcoin block. so that will make financial transactions faster we sent.

It is because that's the feature which makes bitcoin a secure digital currency. People have to wait because every single transaction needs to be confirmed by random people from all around the world. That's how it works.

I have not yet made a transaction where there is double spent but it's likely to happen so users should wait for the confirmation before proceeding,sometimes it takes long time to confirm but this is the only drawback but I still prefer to transact using crypto currency than paypal or payza.

No, your fee will not decrease the time miners need to find a valid block. It will only give miners an incentive to put your transaction into the next block. Raising the fee beyond a certain amount is pointless.

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At the very least this is misguiding, if not plain wrong.

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If only you are in control of your private keys only you can double spend your transaction. Its always the person receiving bitcoin that has to wait for a confirmation, never the one that sends them.

@shorena Thank you for the explanation I really appreciate it.


This is the common misconception I think most of us here believe. The higher the fee, the faster the transaction.  :D

The next block has room for ~2000-2500 transactions (500-400 byte average), if your fee is high enough to be in the top 2000 its enough. You can pay extra to be top 10, but its still the same block.

Yes, in gambling sites - if you invest Bitcoins, play, win and want to withdraw, gambling site will wait for all confirmations before withdraw. It is strange, but most possible gambling sites received some fake BTC transactions, therefore they wait for all confirmations.

Bitcoin do not have a central entity that validates all the transactions being done, because it is a decentralized network. So to simplify things,

the network of people help to validate that the bitcoins you are using in your current transaction, was not spend before. The more people

doing this, the stronger the validation. It is things like this, that makes Bitcoin special.  ;) ... Some of the guys here are too technical.  ::)

I know most people here have already told you it's because of double spending, but I'd like to elaborate on why you so rarely see double spending attempts now: because people wait for confirmations. If people didn't wait for confirmations, there would likely be many more double spending attempts.

Situation is different on many webaite. For example bitpay accept bitcoin payments with only one confirmation. Also there are gambling websites which are immediately adding your coins without confirmation but it doesn't mean they you will withdraw them without confirmation. Confirmation is for to be secure against double spending.
You can see more detailed information here: https://en.bitcoin.it/wiki/Confirmation

Thanks for the link. A very good source of information. Indeed the confirmation of transactions is explained in detail.

they are only irreversible after a certain amount of confirmations, i think its about 6

yes, i agree with the comments here. if we will not wait for the confirmations then we may have double spending those coins. besides its not too much to ask to just wait 10-25 minutes right.

technically its more.. thats why block rewards are unspendable for 100 confirms.

but the chance of a orphan block is 1-2% (atmost risk is 3blocks a day)
in a period where upgrades and consensus changes are happening where pools wont do anything to the blocks unless >95% compliance, means a <5% risk = ~6-7 blocks might orphan

so in a time when there is a bug or a time of consensual feature upgrade where risks are higher, some services may request upto 10-20 confirms, until the risk level subsides.

as for the "trust" / honourability between buyer and seller of zero confirms.. its still not good
some people say its ok to risk $1-2 without confirming.. but.

people buying something for $1-$2 may only see it as value of a loaf of bread in western countries so no big deal.
but people making $1-$2 transaction is not going to pay 7cents-14cents to make such a purchase (7% cost)
so chances are the tx wont even have a fee and it WILL get dropped by the network rather than accepted into a block.

also in the third world. that $1-$2 is a weeks wages. and the tx fee is 1-3 hours minimum wage labour. again chances are no fee added
again dont trust it, if you are transacting with someone from a developing country. treat $2 spend as if they were trying to spend $400 U.S.
you may think its just a loaf of bread. but they think of it as a weeks wage so would be happy to put the effort in to double spend and keep the weeks wage.

its not about how much you spend. its about WHO you are transacting with and the tell tell signs that the transaction may or may not get into a block EG low fee, or opted in for RBF or spot the same inputs being used elsewhere

It also depends on the level of confirmation from the miners, if they have a very fast then the confirmation level we have also quickly. Only now the mining rate is extremely difficult. so I think indeed the level of confirmation right now is very low, it will not be a problem if confirmation still estimate in terms of standards and do not have a low transaction fee rate

Maybe because if you use a low fee, you can revert your transaction.

Also if you don't depend of any confirmation, the blockchain will be useless, the "3" confirmations is something to avoid scammers.

instead of worry about double spend, it's far more likely you will get a tx with too low of fee and it will be rejected before its confirmed.. this has happened to me twice..

in my opinion , wait for confirmation very important because this is ensure really you not other people
and purpose for confirmation is you accept your transaction..

May I ask franky1, shorena, how some casino are able/willing to accept deposits without confirmations?
How do you think they know for sure that the coins were really sent/no double transact?
Is it really just because they control the withdraw process so they can afford the no confirm for deposits? Or are there any other reasons?

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Also, do you know of any way one might be able to calculate the transaction size?

(sorry bout my questions ^^)

I think that before 3 confirmations the transaction is actually reversible.

During the confirmation time you can refund,if there is something wrong with your purchase.

Some people really hate to wait for confirmations and maybe this stops bitcoin growth and mass adoption.

A confirmation means that the transaction is written in a block.
From all I know a block can be mined by two people at the same time, then it takes a little until the network has decided which block it wants to follow.
After a few blocks the network has made that decision.
So it's better to wait that time. Otherwise there is a really small chance that the transaction will be reversed.

there is always some people to play and exploit the system.  And for bitcoin it is the double spend.  The confirmation is the counter of bitcoin system to this kind of bad behaviour.  You maybe don't have an intention to exploit this possible glitch of bitcoin transaction but I am sure there are shady people out there that doesn't care about anything else but to get easy money.

It is done for security reasons and so that you can be protected by yourself and the other user also gets protects himself. If this would not be people would double spend it and it would create caous. It's irritating but it's for our good only. So try and bear with it.

From what i read previously, it is due to avoid something called double spend, even i am not sure how is it work, but its something like in the olden days where ATM in Location A and Location B is not centralized and sync, so people can withdraw their initial deposit twice.

I think its something like that if i am not mistaken

I never get bitcoin twice in a row and within 1 day I did not get any confirmation, and the transaction to fail, it may be referred to must wait until the transaction is getting at least one confirmation only

To prevent double spend, I have never experience it or seen anybody affected by double spend. The issue with double spend is not common again but I was to it was a big issue during Bitcoin formative years

Bitcrap is now up to 16 hours for 1 guy without a confirmation.

https://bitcointalk.org/index.php?topic=1689151.0

 8)

The best answer for this is for security purposes also. Before
we could transact again we ensure that their is no double
spending. Thus, need for confirmation in every transactions.

Because sometimes Bitcoins transaction might not push through because there are times the memory pool of the nodes suddenly clears for some reason. So the transaction gets lost and has to be repeated to get the money. Also, some of them need more than one confirmation; this is really to secure the transaction

To avoid scams.

Bitcoin is based on blockchain, miners have to confirm the transactions so in this way the transactions will be there forever and none can change it anymore, if isn't confirmed, can be an attempt of fraud.

Of course we can't relay on only 1 system for verification of our payment may be he might do some hack and something else to take away my money or if he have full knowledge then he could do anything with my bitcoin so more and more confirmation is good for us.

Hello,

The answer is simple. In order to make your transaction get into the ledger books of bitcoin miners, certain amount of time is needed. If the transaction goes unrecorded then people may not know who has sent the bitcoins to whom and as a result most of the unconfirmed transactions get dropped out of the network.

My wife has 4 transactions stuck in the blockchain since this morning so she can't progress at all in her day to day activities, this is a bit mind bogging and I hope they clear the blockchain soon. So she can't spend anything now.

it's not only about double spend or 51% attack, there are other attacsk that can be done at 4 or 5 confirmations and lower, i think it was called the finney attack in his memory, so to avoid this bitcoin has 6 depth confirmation

I have read mostly the 51% attack but i think this is the first time I read about this finney attack.   So I googled it and see this result. This is kinda tricky because it does not need 51% of the hashrate to do the attack.  For explanation you can read this.  http://bitcoin.stackexchange.com/questions/4942/what-is-a-finney-attack

Some of the notable description on that link

If you send a very small fee then the confirmation time can be extremely long for some people but we must remember that we can adjust the rate of our fee so if we need a fast transaction we can always send a bigger fee and get confirmation in minutes.

Well, I have never meet something like that face to face. This days I make my bitcoins only from the campaing where i am and they transfer me bitcoins buy fact. For example I will get payment for this comment already in some minutes, maximum a hour. Isn't it great?!

by guessing.. since there is no real way to know how much fee you should add.. unless you just add some huge amount.


i sent a tx with .0003 fee and its been 9 hours.. that should have been enough fee for a few minutes, at least it has been in the past..

Yes i agree!bitcoin transaction confirmation plays an important role in every transactions. The reciever can not cancelled the recieving amount and sender could not also cancelled the transactions. Confirmation from blockchain also makes transaction dlow now. Confirmation use to locate if the person really sends bitcoins to the recievers addres.

There is a site that allows you to see with 90% confidence how long your transaction could take depending in the fee you send, I don't post the link because I wont click on a link posted by someone I don't trust, but you can find it very easily by looking for: bitcoin fee transaction.

In a best-case world we wouldn't have to wait at all for transactions to get confirmed, however there is a time between confirmations which is similar (in fact exactly the same) to the time per block in the blockchain. The blocks take time to get confirmed because miners have to find the block. Every block is a confirmation (essentially). The only way to fix this is through shorter block times; which isn't a good idea.

I think because it is need to mine first before it's completed, well if you don't want to wait longer then put a high fee instead of medium fee.

Oh, I would like to know that site, can you please post it here since a lot of people wants to know that or pm me if you want to private it.

Since two people asked for it I'm posting the link which is the next.

https://bitcoinfees.21.co/

The site right now is saying that the fastest and cheapest transaction is 0.0009 mBTC/byte the site tells to you in average the range of time and blocks your transaction may take.

At the moment bitcoin its the most safe platafform to buy and sell or send and receive funds, besides the low fees associated to the size of the transaction, the hash does protect all the transactions, if i have to wait some minutes, that recently is taking hours to get confirmed, i will wait, but are some people that are unhappy with the recent waiting time.

The transaction cannot be lost even if the node become dead for a while,. As the transaction distribute in nodes therefore if one node fell down the other will conform your transaction, in very few cases we have seen that the transaction lost for some other reason but mostly it become confirmed.

There is not much we can do about confirmation time except sending an even bigger fee, but I find that even now the transactions are faster than a wire transfer and if you really need a fast transaction then adding a generous fee will be enough to get confirmation in minutes.

sorry for late reply.

to mitigate risks.
when the casino accepts zero confirms.. they do a few things.

1. they know that when you deposit. your then playing in their house. so while the tx is confirming they can make you lose yor game or hold ot on the withdrawal until the deposit confirms.

2. while unconfirmed, they look at the inputs (where you got the funds) for tell tell signs of risk of it not confirming. EG low fee. or spotting you simultaneously writing a second transaction using the same inputs. opting for RBF, seeing if in the inputs if there was any sign of you trying to double spend before. etc etc.
but point number one is usually the case.. dont pay out unless deposit confirms

certainly bitcoin safe to transact, but everyone when they transact with someone they had to wait until the transaction is confirmed as to avoid losses on certain parties,

irriversable transactions does not means that a user do not have to pay the fees. its the reason for being transactions confirmed but the most importantly it helps us to avoid the problems like double spending and it also makes the avoidation from hackers stronger

This is very important in every bitcoin transaction because it serves as your document incase there is a problem that would happen with your online activities. Online sites handling these specially our online wallets making this more secure in order for the members to gain trust and they became more comfortable as bitcoin is concerned.

Thanks for replying Franky.
So, it really was like that. ^^

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I had no idea there was a service like this.
I always worry when setting my own fees since I have no idea if it would confirm or for how long(hours/days). Which is why I usually end up going with the one suggested(could be costly sometimes,I was once charged $1 for a $35 transaction.) I really wanted to know how to calculate tx size but this service would do.
Thank you for the link.

one of them prevents double spend, all bitcoin transactions are processed by the network blockchain.
during this time I did not must long to wait

Why should people wait for the confirmation of bitcoin? well, to know if their transactions are successfully done or proof that it is already processed. Also confirmation is important because maybe it may become the way or serves as the documentation if what happen to your transactions especially if your first time buying online.

The main reason is to stop double spends, which can be executed far more easily than most people think. It's not done often, but it's a huge problem for bitcoin payment processors. Zero confirmation is done by a select few sites, but those sites always check inputs for confirmations, TX fee, and various things about the transaction. Although it's indeed a long wait for most people to wait for a transaction, it's nothing if you want security.

We should wait for the confirmation because it is a proof that the payment has been already sent to us or to someone who is going to receive a certain amount of bitcoin. It is a proof that we have already paid by someone or we already paid someone, if this confirmation failed, we have to resend the payment that we are going to send to someone because it is really important if we don't want to have any trouble.

I'm sorry does not follow well enough, but it can't be happen if there are sufficient fees right?
Which mean only miners that can be rejected your transaction, and as long as you send enough fee the transaction could consider done?

if the transaction bitcoin you sent is not confirmed, you will not be able to use bitcoin that, you also can not do transactions if bitcoin you sent has not been confirmed, so we have to wait until the first of at least confirm that bitcoin mu can be used, that's the reason why we must wait for confirmation

The time that is attached with confirmation depends upon the fee but the length of time to confirm your deposit at gambling site or exchange is totally depends upon the programming of sites . So its a matter of programme script not of bitcoin payment rule .

I think you can resend the coin to other address thus for the double spend.  It was clearly stated few post above you.

(qouted it to make sure you can see)

This is the reason why establishment wait for at least 2 to 3 confirmation before the amount is credited.

Though a hard thing to do, still the act of double spendig coins is still possible on any transaction, that's why most establishments or online aervices that accepts bitcoin as a payment need to wait for at least 2 or 3 confirmations on the network before crediting the coins on the account. However there are some cases in which sites, especially those related to gambling, do not require to see a skngle confirmation on a tx—they constantly check for the inputs on the tx to ensure that no double spending occurs.

Yes of course we have to wait for confirmation because bitcoin is automated system and there more confirmation means more security. If of someone enter something and try to modify blockchain database then that would be very disappointed.

Confirmation of transactions is some kind of security trigger. Bitcoin system is just functioning that way and this is good to my opinion, that is what makes Bitcoin system one of the safest and prevents double spending. Sometimes is annoying to wait for the needed number of confirmation but we have to accept that.

We can accept those as long those transactions doesnt take days to complete, its something i do believe bitcoin can improve, and i do expect when the mines ends it can be faster, if not on the next years, i do expect bitcoin to be like the credit and debit cards, take few seconds to get confirmed atleast 2 confirmations thats is the most required number to get credited.

Until a transaction has at least 1 confirmation it is not included in the blockchain, and it is good practise to wait at least 6 for more expensive items.

No problem man, that is why we are in the forum in the first place, to exchange information about bitcoin and the related services, I use that service every time I’m going to send a transaction and also as an indirect way to see how busy is the network.

I've never understood the reasoning behind having more than one confirmation, or at least more than 2 or 3. It's not like you can really double-spend after a few blocks have gone through, and it's nearly impossible to reverse a transaction.

I haven't read any papers or gone and looked into why that works in the way it does, but just seems alien to me.

For preventing the double spending, every merchant or store was giving a rule about the minimum of confirmation have needed by them(at least 2). Get the validation from the block.

I want to say only one thing when we make every day transfers, when we go to the bank does the bank says wait a bit until the transaction get listed on the system?
Also when we make international transaction, shouldn't we wait for few days until it gets "confirmed" that's with bitcoin transaction too.

yeah I think it's also happening in the world including many transactions in the bank, but when I do transfer in the bank, I do not need to wait for hours for the money it was acceptable? but in bitcoin might be waiting a long time?

Everytime I made a transactions I always see to it to check the
confirmations of bitcoin. To ensure also that I did not double
send the amount. So this is really important to check in sending
btc to anyone.

it is pretty fun that your transaction may be declined, however that happens really extremely rare.
You can wait even up to 7 days, and you dont know if it is accepted or anything, no sign at all

An unconfirmed transaction is relatively hard to reverse if:
1. There is enough fee attached to it and it probably would get confirmed very soon.
2. The transaction has propagated through the entire network and big miners has seen it.
3. Opt-IN RBF flag is not enabled.

It is safe to accept such transactions if:
1. It is of a relatively small amount.
2. Your business can take the risk.

Ideally, 6 confirmations is the minimum for it to be VERY hard to reverse. The block re-organisation aren't that big and it is very unlikely that 6 blocks would be orphaned. Double spending is still possible if there is a fork and the merchant would lose money if he is on the wrong fork. 51% attacks are extremely hard to pull off and it would have little to no financial benefits.

The reason for many gambling sites to require at least a confirmation is due to the fact that the risk of users double spending is high and they cannot afford to lose any coins.

As long as there is 1 confirmation, you are probably quite safe.

did you mean that we do not need to wait if we send our coins to someone we know for years and we trust him almost 100%? so how do we send those coin without taking too long for waiting? how could it be? probably you can give some explanation or tutorial because I think another OP's purpose asking that question is he wants to know whether any other way to send coins without waiting. cmiiw.

If you trust the other party, you can probably finish the transaction without waiting for any confirmation. You have to trust the other party to not double spend it and you can rebroadcast the transaction yourself from time to time.

The waiting time for confirmation cannot be shortened if they did not include enough fees.

because for verification , bitcoin have a safe security . so this is just make sure you or maybe hacker