Bitcoin Forum

I've noticed several people here making physical notes or coins with Bitcoin values and I'm wondering how they do that. I'm new to Bitcoins but have been making monetary-themed art for many years and it's something I might like to try myself sometime. Making the physical object and its design is easy, but what I'm confused about is how to transfer the actual monetary value from my personal client software to this piece of paper with a number on it. How do you "send" Bitcoins to a physical object instead of another alphanumeric payment address? And do physical Bitcoins have to have a QR code?

It's all public key cryptography. When you go to make a physical object with a bitcoin value, you'll generate a key pair. Write down the private key on the object (As the number itself, or a QR code), and use your bitcoin client to send some coins to the address generated from the public key. Then, anyone who later comes across the object can read the private key off of it, import it to their client, and have access to the funds you sent it.

At least some versions use a scratch off to reveal an address.

That is an interesting question and would like to know the answer. Do you mind if I ask on Rugatu for you and add a reward to it ?

I want an Oreo type cookie that you roll open to reveal the private key.

Don't eat that cookie!

Of course the challenge of any physical version is convincing people the manufacturer destroyed the private keys and can't use them. I think Casascius physical bitcoins (https://www.casascius.com/faq.aspx) handle that well.

Other than that the only real version of physical bitcoins would need to be electronic enabled somehow like the bitcoincard (http://www.bitcoincard.org).

@ Rugatu - Feel free.

@ acoindr - One possible solution to the trust problem might be to give out very small amounts for free, sort of like an offline faucet and as as people redeem them they'll see that they're redeemable. Alternately, people could check feedback on eBay and the like.

That would just show people the ones released were redeemable. If someone was running a scam of course they would make the trap look like it wasn't a trap ;)

The value of every single bill (or whatever) could not be questioned, otherwise people wouldn't accept the value of it, which is a key requirement for something being money. I think the best way to do it is like Casascius and attach a verifiable identity to the addresses used - someone to hold accountable.

Done http://www.rugatu.com/questions/1281/how-to-make-physical-bitcoins

@acoindr - Yes, you're right. I think this is too much for a mere bitcoinnewbie like me to get into any time soon.  :P

It's up to you, but I also do advise people to follow their passion. If it's something your passionate about then do it. If something you're passionate about involves bitcoin definitely do it, you may even make money from it. :)

Don't forget bitcoiners are probably inclined to support such endeavors.

If you buy my sample "roll-your-own" coins, you get a bunch of fresh private keys out of my batch of 29,000.  I generally throw in extra private keys (mostly because they're a bitch to count quickly so I just estimate generously), but if you ask for extras, I'd be happy to oblige, all the way up to a ratio of 2 circles per coin purchased.

By "private key" I mean the little paper circle that contains the actual magic number that allows the funds to be redeemed.  I also provide an instruction sheet to help you find the Bitcoin address that matches the paper circle (it involves downloading a file and finding the address on the list given a few characters printed in green on the circle).

The way it works is simple: send bitcoins to the address, just like a normal payment.  The bitcoins go to nobody - they are in "limbo" on the block chain and can't be spent by anybody until someone reconstructs the private key by entering the black characters on the circle.  Any client accepting "minikeys" will know what to do with the code and will automatically know how to recover the bitcoins and how many were sent to the matching address.

While the paper keys are sized to fit my coins, they can fit in pretty much any object you can shove them in.

physical like a paper wallet?

www.bitaddress.org (http://www.bitaddress.org)

@ casascius - Thanks. I don't have the funds to spare to be buying Bitcoins for something like this yet but when I do I might try it. Are holograms / scratch-offs like you and others use hard to obtain?

@ Hexadecibel - I was thinking more along the lines of what this guy did, https://bitcointalk.org/index.php?topic=52295.0 , but with a more artistic, money-like design.

I wouldn't trust casascius with more money than I would trust instawallet and these are the ones I trust most in the respective areas.
casacius risks big trouble by touching any of his coins as he never knows which ones were unsealed.
instawallet could spend most of the customer's money before anybody would get suspicious.
both services serve me only to get bitcoins in the hands of noobs and never ever would I use any of these as a store of value.
Even if casacius destroys any copy of the key, how can I know nobody scanned it on the way to me? They would have perfect deniability so why would they actually destroy any key at all? It is not possible to prove the destruction of keys.

I assume you know that the private key is sealed inside the coin, right?  The number on the outside of the coin is just the bitcoin address prefix for looking it up.  Unless somebody has some super duper spy-tech to see through the hologram/coin (or if you're talking about the keys I provide for roll-your-owns, which aren't sealed behind a hologram), they're not going to be able to read off your coin in transit without doing obvious visible damage to the hologram.

there's no reason you couldn't generate the keys with bitaddress and slap them on something you made in photoshop or gimp to make it look pretty.

So you take every coin back at the BTC price as long as the seal is not broken?
Aka do you hope for these coins being traded like the real thing?

Not that I had an x-ray at hands but I rather doubt that these coins will ever circulate much as it is far too tempting to get hands on the key.

So long as the seal is unbroken I don't see why people couldn't keep spending a Casascius coin. People would just have to accept this metallic representation of a Bitcoin as if it were a Bitcoin, and it could be passed along, exchangeable for Bitcoins in theory but rarely actually done so, like a gold certificate. That could be good for promoting offline Bitcoin commerce, paying for things in restaurants and stores, giving tips, etc.

Also, I don't think you could read printed numbers on paper with an x-ray unless the density of the ink was significantly different than the density of the paper.

Get a  badge making machine and create buttons you can pin on things that you fill with btc.

People love collecting pins and buttons for some reason. A priv key could quite easily be underneath the cover of it.

My position is as reasonable as I think I could possibly get:  I promise that every coin I sell is an honest coin, and that I have made a reasonable effort to make them snoop-proof given the budget and type of project this is.  I know of no way to snoop the private key out of a coin, and don't think there's any trivial way.  On the other hand, there is no way I can test against every kind of ray, wave, or whatever there may be out there.

It is entirely possible that someone resourceful could figure out a way to snoop my coins, and there is no reasonable way I could be expected to guarantee against that.  If someone succeeded, I'd certainly be interested in buying the coin back off that person, so I could inspect the coin and confirm it was indeed snooped (seeing is believing).  But I don't think I could be expected to buy every coin back from everybody, nor do I think everyone would expect that.

I doubt the coins will be traded much as simple money, mainly due to the markup above face value.  Their main purpose is as a proof of concept, collectibility, and a functional and tangible representation of a bitcoin.  But anyone may do with them as they please.

You got answers  :)

http://www.rugatu.com/questions/1281/how-to-make-physical-bitcoins

Ok, it's getting pointless, but wouldn't the easiest way be to buy exactly the same seals you are buying?

Else I agree that these coins will be what your grand children will stare at with eyes wide open knowing they could buy what not with it.

The seals are custom. And the hologram industry doesn't typically counterfeit to order, any more than you can simply ask a locksmith to make a key to your neighbors house from scratch. Try getting identical seals and see if it's really that easy.

Here in Chile I get keys duplicated for 45ct. the piece. They don't ask anything. Done it many times.

(Funnily you have to register with your RUT (equivalent to the social security number) when entering free, public parks or other random places.)

Of course, but by "from scratch" I mean without the original key.  Something within the realm of a professional locksmith, rather than the newest 16-year-old employee of the local hardware store.

When I had these holograms made, I was required to write a letter to state my legal claim to even use all of the words and images that went into the logo (such as Casascius, the BTC logo, etc.).  For example I had to explain in writing that the BTC logo belonged to an open-source project, that its original author had released it into the public domain (including prints of the forum posts where it was released) and a good-faith assertion that my use of the mark was rightful.  Making holograms requires a much more coordinated effort and high-value assets than duplicating keys, requires a pretty big budget even if you're NOT copying something fraudulently, and sending someone the holograms and saying "can you copy this, hopefully on the cheap" likely won't get anyone very far unless they are very cozy with the people making them.

Other mechanisms for hologram manufacturers are in place to prevent counterfeiting as well, the hologram can be registered on a worldwide database that legit hologram manufacturers will not copy from. So that leaves few avenues for copying the hologram design. Also Mike MAY have other safety mechanisms in place but in order to keep them valid can't disclose them, you never know...