Printing bitcoins, an implementation - page 4.

ribuck

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Quote from: FatherMcGruder on February 22, 2011, 09:48:32 AM

How might one defraud the issuer of invisible ink bitcoin bills?

Photocopy the invisible ink bitcoin bill, and spend it. When the new owner tries to redeem it, they discover that the invisible ink is a lie.

This is not directly defrauding the issuer of the bills, but it would bring the system into disrepute.

Mike Hearn

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Quote from: FatherMcGruder on February 22, 2011, 09:21:30 AM

I rather like it. I imaging that handing a bartender a bitcoin bill could more easily get me a beer than fiddling with a smart phone.

Really? I'd think phones would be much more convenient, if implemented well. Buying beers is always a slow process with cash because of fiddling with change. With an NFC smartphone it could just be take phone out of pocket, unlock screen, tap on the bar ... done.

MacRohard

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This is awesome =)

I really like the idea of printed bitcoins.. if only as a reliable backup mechanism.

FatherMcGruder

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Quote from: TiagoTiago on February 22, 2011, 09:39:18 AM

Is there really no way to read the invisible ink without leaving obvious signs the ink has been seen already?

The probably depends on the particular invisible ink. I suppose some might show under UV, but the issuer could always print the private key on top of ink that also fluoresced under UV.

How might one defraud the issuer of invisible ink bitcoin bills? What countermeasures can such an issuer employ?

TiagoTiago

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Firstbits.com/1fg4i :)

Is there really no way to read the invisible ink without leaving obvious signs the ink has been seen already?

FatherMcGruder

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Quote from: Mike Hearn on February 22, 2011, 08:31:01 AM

I still think handing bitcoin addresses around on paper like this is kind of dumb, but whatever.

I rather like it. I imaging that handing a bartender a bitcoin bill could more easily get me a beer than fiddling with a smart phone. You'd just have to trust the bill's issuer, but no more than you would have to MyBitcoin, for example.

I like the idea of a mutual bank issuing bitcoin bills utilizing invisible ink. Normally, the bill would display a public key that one could use to verify the bill's backing in bitcoins. To redeem these bitcoins, one could apply some ~~heat~~ iodine to the bill, and its invisible ink would display a private key and QR code. Doing so, of course, would void the bill.

http://blog.makezine.com/archive/2008/11/invisible-ink-printer.html

Mike Hearn

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This is using a format you just made up, there's no such thing as a bitcoin:priv= URL. You should be using the format I just made up instead Wink

v=1
base58 encoded privkey,block number

See the other thread where Hal posts a similar challenge for the real "spec". I could take these coins but somebody else can do it this time. Once is enough.

You appear to have provided a privkey in ASN.1 format. That's inefficient. You only need to provide the 256bit number. Less data makes for QRcodes that are easier to read.

I still think handing bitcoin addresses around on paper like this is kind of dumb, but whatever. If you're going to do this, we might as well try and standardize it!

FatherMcGruder

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Quote from: Binford 6100 on February 22, 2011, 04:49:55 AM

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

Well, my coding experience consists of me floating through CSE 123 eight years ago and then a little bit of Matlab here and there. So, pardon me for looking for something along the lines of the OP's link but in reverse.

Nefario

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GLBSE Support [email protected]

I like the paper version.

db

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Quote from: ribuck on February 22, 2011, 06:28:29 AM

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

https://bitcointalksearch.org/topic/m.46648

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.

db

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Quote from: Nefario on February 22, 2011, 06:21:39 AM

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.

ribuck

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

https://bitcointalksearch.org/topic/m.46648

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

Nefario

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Activity: 602

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GLBSE Support [email protected]

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?

db

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Activity: 279

Merit: 261

Quote from: Nefario on February 22, 2011, 05:37:13 AM

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.

BitterTea

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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.

Nefario

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GLBSE Support [email protected]

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

Binford 6100

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PGP OTC WOT: EB7FCE3D

Quote from: FatherMcGruder on February 21, 2011, 08:08:23 PM

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.

JollyGreen

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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

JollyGreen

newbie

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following instructions from the other forum post,

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

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

JollyGreen

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Quote from: N12 on February 21, 2011, 11:57:46 PM

Quote from: Nefario on February 21, 2011, 11:55:07 PM

Quote from: JollyGreen on February 21, 2011, 11:46:40 PM

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

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