Topic: What do confirmations mean? If your transaction is confirmed is it guaranteed? (Read 998 times)

Will the first transaction get a conformation of some random one? If its the first on then simply send it to yourself first and the to other vendors so that you can keep your coin too!

^ this

It is only 8 pages long and has lots of pictures.  It isn't filled with overly technical language.  Take an hour and look at it.  You'll probably be pleasantly surprised and wonder why you didn't look at it sooner.

Thanks everyone for the great info. I guess I was concerned about Cryptsy losing their records and claiming I never sent them my coins when in fact I have thousands of confirmations.

I guess my only concern is them going out of business and stealing my coins that way.

Bitcoin uses a probabilistic consensus algorithm to solve agreement (on the blockchain)

It takes, on average, a lot more time to solve a block than to broadcast it.
The idea is simple and elegant. The longest chain is considered truth while discarding the others.
Imagine a scenario where two miners/pools find two solutions at roughly the same time. If they broadcast their solution how do you decide which one is "the right one". (discard numerical value of the solution here for an instance as it is easier to describe this way)
Because it is not deterministic when the next block is solved, it becomes unlikely that both new chains grow at the same speed. Furthermore, because one of the concurrent chains will HAVE to be discarded eventually miners will try and stick with the longest chain. Double spending would occur if a transaction is done on a block after which a concurrent, longer chain is revealed that does NOT contain that transaction.
Obviously, the more blocks come after a block with the relevant transaction the less likely it becomes that a hidden, longer chain is revealed ( as this then takes more and more computational power to produce)
So ultimately, the lowest block on the chain is the one with the most certainty, eventually converging to a probability of 1 of never changing again

thanks!

Off topic but it looks like one of the only alt coins that is not a simple fork or clone of Bitcoin:  https://bitcointalksearch.org/topic/ann-emunie-emu-not-a-bitcoin-forkclone-call-for-beta-testers-220530

You aren't the only one. I keep telling myself that I will read the white paper and won't stop until I understand at least 60% of it, but I never get to it, lol.
Anyway, using a tree structure would make a bigger mess then a chain if you ask me. How would you even organize such monstrosity? Do you order it according to hash, to it's current number? Do you even order it and if not, why not? Isn't that kinda the point of a tree?

It's interesting, but that is about it. Using a tree sounds like a stupid idea's in my ears, but oh well, what does a IT student know, right?
Could you link me to the Altcoin that uses it?

They claim using a tree structure rather than a chain allows them to fix the zero confirmation double spend issue.  However, I have not studied it yet.  I barely have enough time to study Bitcoin.  I have been involved with Bitcoin for almost three years now and I still learn new things about it on a weekly basis.

I wonder that too. I don't see how a tree would be better then a chain, lol.

A bit more on this.  How can a vendor accept BTC and ship you the product instantly and still be somewhat protected?  This is not a trivial issue and actually is a topic of a lot technical discussion by the developers.

We actually need this if BTC are to be accepted at for example Starbuck's.  You want the customer to be able to pay for their coffee and then get the coffee without having to wait for the first confirmation.  Also note that 10 minutes for a confirmation is an average time.  It can be anywhere from a few seconds to hours before the transation is placed into a block in the blockchain.

One proposal is:

Wait to see the broadcast of the transaction to the network (almost instant).
Wait about 15 seconds or so to make sure that another spend of the same coins does not happen from anywere else on the planet.  That is about how much time it takes a broadcast transaction to propagate through the world wide network.

Can this still be gamed?  Yes.  In fact the customer can get their coffee, sit down at their computer and spend that same coin somewhere else on the internet.  However by waiting the 15 seconds Starbuck's is confident that their transaction will be first in line at all the miners in the world.

There is one serious hole in this method.  If the Starbuck's transaction has a miners fee of say 0.0001 and the second transaction has a larger fee of say 0.0002 then some of the miners may pick the second transaction to include in their block and drop the first one.  If they do that and they win the block race then Starbuck's is out the money for that transaction.

This is totally untrue.  You are mixing up two totally different topics.  Please do not do that as you will just confuse yourself and everyone else.

Topic one:  a 0 confirmation double spend
Topic two:  a 51% attack on the Bitcoin network

Since this thread is about confirmations and not about network attacks I will not address a 51% attack here except to fix your comment and say it does not belong in this thread:

Now, fixing the rest of your comment:

A double/multiple spend is very simple if you have two or more vendors that accept your BTC with zero confirmation and instantly ship you the product.  Here is how you do it:

You have an unspent output of 1 BTC
You send it to the first vendor's address, they accept the coin with 0 confirmations and ship you the product.
Now you have about 10 minute before the transaction is put in a block and gets the first confirmation
So, you simply log into the second vendor site and send the same coin to them, they also accept the coin with no confirmation and send you the product.
See?  You can spend that same coin as many times as you want.

Eventually one of the spends will get confirmed and all the other spends of the same coin will get dropped.

One vendor will get paid, all the rest are screwed because they have shipped the product and got nothing for it.

Wow, how does that even work?

You used to be able to here: https://blockchain.info/create-double-spend, but they took it down...

Once you get a conformation then most likely (99.999999999%) its guaranteed. The more conformations you get though, the better/safer!

For the most part, transactions that have been broadcast to the network with 0 confirmations are pretty much assured to "go through."

In order to successfully broadcast a fraudulent transaction, one must have a warehouse worth of computing power at his disposal, and a hell of a ton of luck.

There is one that uses a block tree instead of a chain but still a public record of all transactions.

I believe all of them, and I would be surprised if there's other way to build a cryptocurrency. I mean, if it's not a blockchain, then it's a centralized database, right?

That's great news.

If I sent bitcoins (or any other cryptocurrency) to someone and they say they never received the transaction I can prove it by showing them the block chain?

Do all other cryptocurrencies have block chains or is it just bitcoin?

If a transaction is in the block chain, then the receiver has (by definition) received the bitcoins. Remember, bitcoins are not stored in a wallet, and bitcoins are not actually sent anywhere. Bitcoins are stored in the block chain and a transaction simply changes ownership from one address to another.

The first confirmation happens when the transaction is added to the block chain. Subsequent confirmations increase the confidence of the transaction.