Printing bitcoins, an implementation

[db]

There has been much talk about printing bitcoins. Here is a program to do it.

http://bitcoin.modernjob.info/print.html

It takes a wallet.dat file and generates PDF and EPS bitcoin cheques looking like this:




Each bitcoin address in the wallet with available coins gets a note containing the amount and the private key that controls it, both human readable and in QR Code.

(The notes above are real. The first person to take them gets them.)

Edit: PDF / EPS link.

[N12]

So how should I use this without the according public key? I like this idea though. You could use that as a physical backup if combined with the public key.

[db]

So how should I use this without the according public key? I like this idea though. You could use that as a physical backup if combined with the public key.

The public key is derived from the private key.

[Binford 6100]

(The notes above are real. The first person to take them gets them.)

user Hal organized a similar quest on weekend
his was a bit more complicated (he provided us with a base58 encoded pvt key and for the first round with an invalid key : )))
at least 2 people have a valid implementation for spending transactions based on private key
if they find out, they might claim your bitcoins instantly by reusing what they wrote for the Hal challenge.

[FatherMcGruder]

How does one convert those paper bitcoins back to electronic ones?

EDIT: Just found this thread. Seems complicated.

[JollyGreen]

I have tried several QR decoders that are free on the internet and none seem to be able to read the images or cropped images.  Has anyone been able to decode these QR images?

[Nefario]

I have tried several QR decoders that are free on the internet and none seem to be able to read the images or cropped images.  Has anyone been able to decode these QR images?

+1, QR decoder libraries

[N12]

I have tried several QR decoders that are free on the internet and none seem to be able to read the images or cropped images.  Has anyone been able to decode these QR images?

+1, QR decoder libraries

Works for me with Barcode Scanner on Android. Still, I don’t know how to get the public key out of the private one.

[JollyGreen]

I have tried several QR decoders that are free on the internet and none seem to be able to read the images or cropped images.  Has anyone been able to decode these QR images?

+1, QR decoder libraries

Works for me with Barcode Scanner on Android. Still, I don’t know how to get the public key out of the private one.

Well, I'm not sure you would have to if you just insert it back into a wallet.dat file and then use bitcoin to open the wallet.dat

[JollyGreen]

following instructions from the other forum post,

here is the block for the "1.0" BTC bill.

http://blockexplorer.com/address/1BNiV3yU9VjdAgHDtdN3rNYT9MbhuNLw2Z

[JollyGreen]

So, I guess we do need to compute a Public Key from the private.  If you look in "key.h" in the BitCoin source there is a function "GetPubKey()".  It is calling a function "i2o_ECPublicKey".  I've spent way too much time on this for one BTC   Hopefully someone else can figure this out and create a python interface.  I would contribute more BTC but I only have "0.11" haha

[Binford 6100]

How does one convert those paper bitcoins back to electronic ones?

EDIT: Just found this thread. Seems complicated.

yes, it's been solved on weekend in the forum you found
Prize for importing private key [WON]

and when the folks who solved it find this forum, they will just run the apps they wrote with the keys
from the banknotes.

what  you can do is PM them with link to this forum and ask for a small tip, share of the bounty, imho

it's not that complicated. just 3 or 4 steps but requires some coding experience.

[Nefario]

So with a few extra coded tools this could make bitcoins easily transferred via paper? Or even better, with mobile phones(android, iphone)?

[BitterTea]

You know, when you're transferring BTC this way, maybe you don't even bother importing the private key into a wallet. You could scan the block chain looking for the coins associated with the key having been spent and create a transaction using that key, sending to another Bitcoin address you control. Broadcast to the network and wait for a confirmation. That way they can't spend those coins after they have given you the key.

[db]

So with a few extra coded tools this could make bitcoins easily transferred via paper? Or even better, with mobile phones(android, iphone)?

As long as you trust them to give you a valid note or can verify and claim it before you let them out of your sight. Still, printed bitcoins could even work in a grocery store. Scan the note with the barcode reader and immediately check that the coins are not spent and that there is no double spending announced. Print the change on the receipt.

[Nefario]

Nice but doesn't this take some time for there first to be confirmations? Wouldn't that kind of make it a little less practical to use?

[ribuck]

Hey db, this is very nice, but would you consider modifying the program to use the terminology discussed here?

http://bitcointalk.org/index.php?topic=3311.msg46648#msg46648

That way it will be tidier when we get down to the smallest subdivisions of a bitcoin.

[db]

Nice but doesn't this take some time for there first to be confirmations? Wouldn't that kind of make it a little less practical to use?

As discussed in the fast transaction acceptance thread you don't have to wait for confirmations. Just check that no double spendings are announced. Then the only way to do fraud is to have found a block in advance that spends the coins. In a mature Bitcoin economy that is expensive and very unlikely as there will always only be about six blocks per hour.

[db]

Hey db, this is very nice, but would you consider modifying the program to use the terminology discussed here?

http://bitcointalk.org/index.php?topic=3311.msg46648#msg46648

That way it will be tidier when we get down to the smallest subdivisions of a bitcoin.

If / when we get down to the smallest subdivision we will have much bigger problems than having to call it "10 nBTC" (what's even bad about that at all?). All the inconsistency and confusion from changing the basic unit to bitcent (what is the proposed three letter(?) abbreviation for that by the way?) and mixing powers of 100 and 1000 is not worth it to solve something that isn't even a problem.

[Nefario]

I like the paper version.