Bitcoin Forum

I wanted to test Bitcoin's double-spending protection, so I copied the wallet.dat file to another folder. I had 1.21 BTC as my balance, and I donated 0.01 BTC, and then exited the program. I then moved the copy of the wallet.dat file back to Bitcoin's AppData folder, and started Bitcoin.

When it started, it showed 1.21 BTC as my balance, but a second later, it became 0.00.

Is this there on purpose to punish people who attempt double-spending, or is it a bug?

(All my transactions are present in the window. My balance is at 0.00 though.)

hmm that indeed seems odd.
if you still got the other version of your wallet.dat try to use that.

The 1.21 BC was in a single "chunk". When you sent 0.01, you made a transaction with one "in" (the "chunk") and two "outs": one sent 0.01 to whoever you sent that to, and the other one sent 1.20 back to you as "change". This second "out" was sent to a brand new address that you just generated. Since your old wallet.dat doesn't have the keys to this new address, you don't see it.

Ah, okay. So I guess that my 1.20 BTC is lost forever, unless I try to recover the file with a data recovery tool.

If you want to do that you should do it as soon as possible because every new write-access could overwrite the sector where that file is still stored.

When you copied the copy of wallet.dat back to the Bitcoin AppData folder, did you overwrite the existing wallet.dat?

This is certainly REALLY SCARY since that's how people do backups.  What is the procedure to do backup and restoring backups???

Yeah, I just overwrote it. I'm not gonna bother trying to recover the file. It was only 1.20 BTC and I'm not gonna sweat the small stuff.

The wallet.dat now has transactions that don't reflect the current balance, so I'm just going to delete it.

Luckily, I only had 1.20 BTC to lose, but backing up the wallet should be definitely integrated into the client.

While they're doing that, they should build in a way to "bank" your coins into encrypted files.



Well, I guess the BTCs value just got a tiny bit higher.  :P  ;D

A tiny bit now, but in a couple years?  Here's a snippet from my IRC bot.
According to http://www.census.gov/main/www/popclock.html the world population is 6,855,970,029. If everyone had the same amount of bitcoins, everyone would have 0.00306302 bitcoins.  If 0.00000001 bitcoins were equivalent to US$0.01, then everyone would have equivalent of US$3,063.02389176 and the value of all bitcoins would be equivalent of US$21,000,000,000,000.00.

Here's the new link: http://www.census.gov/popclock/

In over five years, the population now exceeds 7B and bitcoins are worth way more than fractions of a cents, in fact, there's virtually a parity with the two abstracts when considering its market cap.

Of course, the percentage of the world population who would actually want bitcoins will probably stay at 0.001 or less.

The percentage of people who own USD is close to 5%, so consider that ;)

you have your wallet destroying data. You really lost all his bitcoin  :o

When Bitcoin gets cracked it will mostly likely to be worth exactly $ 0.00

you obviously don't understand what 'cracked' is.  Not going to happen.

The most retarded aspect of bitcoin, regardless of how safe it is. I am always using just one address and sending everything even with altcoins there. The new multiaddress GUI is so fucking confusing.

lesson to all.. learn your privkeys!!!

save your privkeys as they are the important part. dont just rely on having a wallet.dat file in a second folder.

not only can u mess things up by not copying the file correctly. you can also get viruses, house fires, burglars stealing your PC. a disgruntled employee/spouse putting a hammer to your device.

so learn how to get your privkeys and back them up in a new location..

the reason why the OP lost his coins is because when he sent the 0.1btc out it also takes the 2.0btc with it and returns the 2.0 to a change address.. this change address is saved to the active wallet.dat.
the problem is that if he had a wallet.dat backed up from hours/days before the tx was sent. then the backup wont contain the privkey/pubkey of the change address..

No. Lesson to BTC DEVS - learn basics of end user experience. Drop your Microsoftian attitude, please. It's 2015.

Do you still have your backup intact? Why on earth did you want to try double spend with 1+BTC?

no one should be backing up their wallet.dats as the change addresses mean you have to constantly update. i would say that bitcoincore needs an easy way to File->save the privkeys as having to explore your program data folders is just silly

Why should btc devs care about user's funds?

I assume they want more people to use bitcoin would be the answer.  People have different levels of technical experience and limited time/resources to learn new things in life.  

I assume they want to feed their children and wifes.
And this reason is much more significant.
Sometimes it is contrary to what you've said.

That just might not be how things work? The dat file does not contain your transactions and coins.. it is just an address, a wallet.. the coins and its whereabouts are in the chain, regardless of wether or not you have a backup. It would be stupid if you send your coins, than put back your backup and have back your coins again..

If I have a paper wallet, I can have coins on it and spend them, without having to print out a new wallet everytime I use it.. the blockchain ledger is keeping the books, not the dat files.

Double spend testing should be done without the risk of losing too much.

i think that amaclin is trying to say that the bitcoin-dev's main priority is the network and ensuring it cant be abused.
by this i mean the bitcoin dev's are the equivelent of the bank wire transfer team.. and there should be another team who program the user GUI, much like banks have a website dev team, separate from the payment network.

i personally reprogrammed my bitcoin core to be more user friendly, and there are other wallet programs/websites that can take care of the GUI side of things.
EG blockchain.info allows users to send funds, and backup privkeys. even ensuring the change returns to the same address as it was sent from.

i think once bitcoin-core is at a V1 status (not in beta), the programmers would divert the concentration from security and more towards user friendlyness.. but to me i think any naive, newbie, non miner should start off with other wallets. and later move onto bitcoin-core once their funds need to be secured away from third party services and once they learn to backup privkeys

No. I want to say that if you pay nothing for developers you should not ask anything.
Banks take fees and pay these fees to their developers.
Bitcoiners are proud of fee-free transactions.
But what is the reason for any developer to do things for free for you?

well the reason they do what they do is because it protects their own investments.. which as a by-product protects everyone elses too. their priority is security of the network. not so much the GUI.
however i do agree that if people want extra features they could request the bitcoin-dev team to set up an address so that people can send a donation to. because thats how politics works. corporations pay politicians in exchange for regulatory benefits or tax breaks.

maybe worth people who want certain changes to talk to the bitcoindev team, and the team set up a kind of 'go-fund-me' site that lists an address next to a features description. then those that want that feature to be dealt with, can fund it to happen.

short-trading may be more profitable for "protecting investments" :)

Any proof that somebody of them said that?

Some people just do not want to collect donations.

Take what you can give nothing back - Jack Sparrow
http://www.youtube.com/watch?v=VWlfcs9ablg

i meant they need to prioritise security to ensure bitcoin itself doesnt fail making everyones coin worth nothing.. which no 'trading' will help profit from if bitcoin is worthless, so making sure bitcoin doesnt fail as a payment service with limited supply is top priority, not just for their own investments, but yours too

yes for many years gavin andresen has said it himself, along with most of the rest of the dev-team

OP never mentioned about checking his funds in explorer. Do not try unknown things always.
Do only things what you are sure about. Playing with wallet files are not recommenced even for experienced people also.

It was 2010 and 1.21 BTC was worth nothing. The core wallet.dat file now contains pre-generated change addresses to mitigate things like these. If it wasn't for these experiments we might not have this feature.

Exactly this! We need unfortunately many failures like this to learn from them and improve software and user experience of the Bitcoin. It's actually like that in every industry today all over the world. Nobody is so smart to anticipate every single thing that can go wrong. We live and we learn and I am OK with this, even if one day I might be the one that will pay the price.

Edit: And I love the option that I can have many different addresses so I can give each address to the person I wish to.

I do not believe trusting the wallet.dat file should be your only option to secure your wallets future. I have seen too many times, how files get infected or targeted and then become inaccessible to the users.

I always resort to a physical printout of the private key to secure my coins. This is something that has to be addressed by the core developers and engineers, because many people are clueless about these technical things.   

I am kind of a noob and learnt today that to make a backup you only have to backup the wallet.dat. I was surprised that it was so simple.

To restore a wallet you only have to overwrite the wallet.dat then?

Very bad 1.21 BTC is very huge you lost with a double spending bitcoin error.

Why in the world would you try and double spend in the first place? Seems like a stupid idea.

Right.  So why are they not showing.

Does OP simply need to do a restart with -rescan?

u will be very lucky if u get this coins back

on the other hand - you just put bigger value to BTC due to more lost coins that will never move!

I don't think this is a case of double spending. It is just a case of accidentally deleting a wallet.dat file. Never overwrite a wallet.dat unless you are very sure there is nothing inside (or no one will send anything to the addresses).

This is a nightmare. you have a loss of the most important key..

It is not just simple "caring about users funds" matter. It is about creating something good and reliable for people to use.
If you have to be IT engineer to be able to manage your bitcoins well and you need to special training to be able to copy your btc, then something is not right here imo.

That's very odd. This is very similar to doing a backup and restoring it later.  if that actually happened isn't there any way to find out what is this new address?

Lost forever?  Sad to hear that.

i never had a lots of bitcoin but i am a trader and i happen to use a very risky strategy, and every week i loose all of my bitcoins which i make from diversified sources. what i do is i trade on secondstrade, it is a binary options strategy which gives you better odds than compared to the regular binary options brokers.

Nope a rescan would not help because the keypool feature did not exist yet at the time. This thread was created in July 14, 2010, while the keypool feature was first added to the bitcoin qt by satoshi in October 09, 2010. https://bitcointalk.org/index.php?topic=1414.0.

Let me see if I got this right. So if you have a certain amount at an address and send out part of that amount, EVERYTHING you had at that address is moved out and the change is deposited at a new address? Why isn't the change kept at the original address?

the safe way is not to look for 10% spreads and hoping to double your money over night. just look for 1% spreads, even trading 1 time a day means that you will double your money in 3 months and have 400% profit in a year. and thats just from one trade a day

The major reason is to give users better privacy. If there is no change address, someone else monitoring my address will see how much I have spent my bitcoin every time I make a transaction. But if there is a change address, you will only see I have send some bitcoin to address A and some bitcoin to address B, without knowing which of the two addresses is my change address.

They havent even cracked sha2 and if the day comes that sha256 can be broken, bitcoin can switch very easily to sha512, sha1024, etc, etc, so no, it wont be broken ;) Destroyed by regulation s maybe, but not the code being broken :)

Thanks for replying. So if I have a backup of my wallet.dat file I need to make a new backup every time I send coins, because there's always the possibility that the change will be moved to a newly generated address (if it runs out of pregenerated addresses or something) that doesn't exist in the backup file, right?

Can someone explain me this. If you send it and it changes addresses, you still have the .dat file to which you did the tranfer. If you take THAT .dat file, like stated in the OP, you should have all your funds right, because its the same .dat fi,le as is used with the transaction, since he overwrited it.

What am I missing ???

What is odd?

If a writer has written 200 pages of his book and have it in a wordpad-file. Then he removes that file and open the last backup that only contains 50 pages.. well it will only show 50 pages and not 200, this is not odd. Make a backup everytime you use your wallet and save the old backups just in case.

Yes but he took a old backup and replaced it with the latest wallet.dat after he sent some btc. Make a backup everytime you have sent/received coins.

Wow.
Imho such privacy implementation, though very useful for some, should not be the default. Maybe a check box could switch between 2 modes. I know that this is not gonna happen though.
Most users, especially the beginners, especially the people with small amounts, don't need such advanced privacy.
I am glad I don't use btc core, I could have faced this same issue, because I also expected the change go back to the initial address.

Once again, I suggest the newcomers use simpler wallets than the BTC core.

Wow, I did not know that either!! I thought having a backup of my wallet.dat would be enough.... Very useful information, should really be combined with the Bitcoin Core wallet. In fact, if it were up to me I'd have the wallet auto-backup the wallet.dat after every payment.

It's really too bad developing the Core wallet to something actually useful to end-users is so low on the agenda. I really don't understand why =(

Edit: Found a good answer already from a Gulden (NLG) dev how wallet.dat backups work: https://bitcointalk.org/index.php?topic=554412.msg12623914#msg12623914