Printing bitcoins, an implementation

[FatherMcGruder]

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.

[1714845861]

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[Mike Hearn]

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

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]

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

[TiagoTiago]

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

[FatherMcGruder]

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?

[MacRohard]

This is awesome =)

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

[Mike Hearn]

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.

[ribuck]

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.

[FatherMcGruder]

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.

Emphasis on "implemented well". Some smart phones stink ("hold on, I have to run app-kill") and the prospect of getting drunks and technology to play nice doesn't sit well with me. An electronic system would have to work easier than a paper/plastic one. For example, the bartender would tell me the price, I touch the screen no more than once after unlocking my phone, wave it, and get beer. Having to aim the phone at a QR code or coordinate precisely with the bartender won't work.

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.

The issuer can employ watermarks that show up on photocopies, as banks already do with checks.

[myrkul]

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.

The issuer can employ watermarks that show up on photocopies, as banks already do with checks.

Better idea, Scan the note, digitally process it to bring out the private key (using filters, perhaps?), transfer the money out, then spend the original, now worthless, paper.

Seriously, though... When even the dude in the mud hut in Zimbabwe has a smart-phone, Do we really need paper money anymore?

[Binford 6100]

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

we'll be doing the scratch card method prints
QR code of the funded address is visible
QR code of the private key is under a layer of metallic paint

see DIY howto here http://artmind-etcetera.blogspot.com/2009/05/how-to-make-scratch-off-lottery-tickets.html

that way no need for invisible ink and co, just print all data and cover the sensitive parts
also no need for standardization. printouts will remain a marginal form of btc circulation, more or less as gift cards
 +a way to build reputation in community (issuing printed btc requires audience that trusts that they will not be spent by issuer)

[myrkul]

that way no need for invisible ink and co, just print all data and cover the sensitive parts
also no need for standardization. printouts will remain a marginal form of btc circulation, more or less as gift cards
 +a way to build reputation in community (issuing printed btc requires audience that trusts that they will not be spent by issuer)

This. Scratch cards are the way to go, if you're going to print the things...

And yeah, I can see grandmas sending scratch card bitcoins to kids every christmas. Heck, they might even make cards with the BTC already printed on them.

I can also see the news story when a whole bunch of them get to their recipients already spent because some unscrupulous employee snagged the Private keys off the cards before they got their protective coating of scratchy-paint. (Possible, but very difficult... involves a hi-speed digital camera and the willingness to place pieces of yourself close to machinery that's moving very very fast.) Remember, parents, verify before you buy!

[grondilu]

Interesting concept of a "bitcoin note".  I also like the design you suggested.

However, such a note is different from usual bank notes, since it has value only during a limited period of time.  Basically until someone redeem  the bitcoin on the address and transfer it to an other address.

That's why I think there should be a note saying what exactly this is.

Something like:

<< This is a private key of a bitcoin address which was holding 1 BTC at block number NNNN. >>

[FatherMcGruder]

Better idea, Scan the note, digitally process it to bring out the private key (using filters, perhaps?), transfer the money out, then spend the original, now worthless, paper.

But the ink is invisible. There's nothing to filter.

we'll be doing the scratch card method prints
QR code of the funded address is visible
QR code of the private key is under a layer of metallic paint

see DIY howto here http://artmind-etcetera.blogspot.com/2009/05/how-to-make-scratch-off-lottery-tickets.html

that way no need for invisible ink and co, just print all data and cover the sensitive parts

What's to stop someone from painting another scratch-off layer?

also no need for standardization. printouts will remain a marginal form of btc circulation, more or less as gift cards
 +a way to build reputation in community (issuing printed btc requires audience that trusts that they will not be spent by issuer)

It'd be nice though to just use a code without having to figure out which standard it followed.

[myrkul]

Better idea, Scan the note, digitally process it to bring out the private key (using filters, perhaps?), transfer the money out, then spend the original, now worthless, paper.

But the ink is invisible. There's nothing to filter.

It's invisible to every specrtum of light, or just the human-visible ones?

[FatherMcGruder]

It's invisible to every specrtum of light, or just the human-visible ones?

Let's say you have ink that is invisible to human eyes, but it is visible in IR. You could just print it on top of ink or paper that is as visible in IR. You can do the same with UV too. Beyond the UV to IR spectrum though, the cost of trying to read this invisible ink gets high. The issuer can avoid this problem by not letting the note represent too many bitcoins.

[myrkul]

Or... He could cover the sensitive data with metallic paint. Works fine for the lottery.

Global community note: in the US, scratch cards such as ptmhd suggested are used extensively, in raffles of all kinds, but mostly in state-run lottery schemes. They are priced at 1-5 dollars per scratch cards, and have prizes in excess of $1000, depending on the state and card. It's a proven technology, and fairly secure.

That said, I don't see why BOTH technologies couldn't co-exist, though I do lean towards scratch cards being more economically viable. (code + paint vs code (special ink) + UV layer (special ink) + IR layer (Special ink) + solvent to redeem)

[ribuck]

scratch card ... fairly secure.

It's secure for the issuer, because there's also a checksum printed on the card. But it's not so secure for the layperson, who depends for security upon buying the scratchcard from a trusted vendor. As these scratchcards are not widely used as money, that's good enough.

[FatherMcGruder]

Or... He could cover the sensitive data with metallic paint. Works fine for the lottery.

Global community note: in the US, scratch cards such as ptmhd suggested are used extensively, in raffles of all kinds, but mostly in state-run lottery schemes. They are priced at 1-5 dollars per scratch cards, and have prizes in excess of $1000, depending on the state and card. It's a proven technology, and fairly secure.

That said, I don't see why BOTH technologies couldn't co-exist, though I do lean towards scratch cards being more economically viable. (code + paint vs code (special ink) + UV layer (special ink) + IR layer (Special ink) + solvent to redeem)

But one only has a small probability that cheating a scratch-off game will earn a reward. Assuming an honest issuer, freshly issued notes carry a probability of 1 that they represent bitcoins.

Scratch-offs would only work if the issuer printed a difficult to replicate but easily verifiable image on top of the scratch area. That requires three layers of printing, versus one or two for invisible ink. Therefore, scratch-off bitcoin notes are more expensive and must represent more bitcoins to offset their production cost. Subsequently, they are a nicer target than invisible ink notes.

If the notes are cheap to produce then the issuer can afford to periodically recall notes and issue new ones. This way, the issuer can keep up with technology, preserve the value of his notes and reclaim the bitcoins associated with lost or destroyed notes. Holders who can't bring their notes back to the issuer to receive new ones can just reveal the invisible ink and redeem the bitcoins themselves before the end of the recall period.

Here's how I think a one bitcoin note might look. I'm happy to share the .idw file if anyone would like.

[bitk]

here in Italy, 100% of the cards for buying phone prepaid credit are scratch cards, instant lottery tickets are scratch cards, etc... I've never heard of someone buying a card that was used and re-printed with the metal layer.
OFC I must say usually you don't buy them from other people but from "commercial entities". Still, if one can quickly check if the money is in the process of being double-spent, this is still way more safer then cheques.