Physical bitcoins, take 4

[DataSurfer]

So this would be a bitcoin "check" or giftcard that anyone could clear.  Great for a one time usage scenario.  I promote bitcoin by handing out bitcoin "checks" with 5BTC on them.  And once redeemed they would be valueless and useless.

In theory you could pass on the "check" without actually redeeming it, but this would be dangerous as you wouldn't know if anyone up stream had copied the private key on the check.  Nor is there a guarantee that the check issuer did not retain a copy of the private key.

This is not the same as a physical bitcoin backed currency.

Ooh,  I just thought of something.  Public key hardened checks.  I write you a check and sign the amount over to your public key.  The bank only clears the check if you can sign a deposit slip with the corresponding private key.  Maybe too much work for a system not generally regarded as broken.

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[MoonShadow]

By the way...  Any thoughts on this item?

http://www.chrismartenson.com/forum/defendant-convicted-minting-his-own-currency/55031

Another case for using paper, I should think.

Plastic casino chip like tokens would work well too, and could use RFID tags inbedded into the plastic to hold the public key.  And even the private key could be micro-etched onto a thin piece of metal imbedded into the plastic, so that the holder of the plastic token could tear it apart to get at the private key.

[FatherMcGruder]

If the serial number on the paper is a public key then any client can verify that real bitcoins back up the paper. The key would have to own exactly the stated amount on the paper.

Any holder of paper can go back to the issuing institution and "transfer" the value to a new piece of paper with a new key on it. The holder can verify that the transaction went through on the real bitcoin side. This action would render any "duplicate" pieces of paper useless because if they now check their keys there is no value behind them. It would take a real juggling act for the issuing institution to keep any fraud from showing.

It wouldn't take too many people regularly checking their paper bitcoin to ensure the issuing institution is backing the paper with 100% real bitcoin.

The only risk is that the issuer might assign a certain amount of bitcoins to more than one bill.

Is there really an invisible ink that lasts forever (or for years at least) and absolutely cannot be revealed by any method that doesn't render it permanently visible? If so, I suppose that works. The issuer wouldn't even need to retain his own ability to access deposits, if he was willing to let some bitcoins be potentially lost forever. If not, then the idea doesn't work, no matter how cool it would be.

I'm confident that a concerted engineering effort will yield a secure, redeemable bitcoin note whether or not it employs invisible ink.

I'm wary of any attempt to make notes self-redeeming, because it is basically DRM---you are giving out the keys to the vault in an obscured form, so that people can only use them in the way you would like. We all know how well this has worked for software and movies.

It's not DRM because the holder of the note because beyond what would be a simple process of redeeming the note, the users would have the bitcoins in electronic form with which to do whatever they want.

I'm smart enough to know I'm not the smartest man on the planet---and whatever scheme I come up with for hiding private keys, one of those smarter men will find a way to reveal them without voiding the note. If he's smart enough to keep his mouth shut, he could do this for years before anyone even notices there's a problem. It would be negligent of me as a guardian of deposits to leave them vulnerable like that.

That's why the issuer would recall the notes on a scheduled basis and issue new ones with different technology. Cheaters wouldn't be able to keep up.

Paper currency has its vulnerabilities, but it has its benefits too. Some might find that the latter outweighs the former.

And even the private key could be micro-etched onto a thin piece of metal imbedded into the plastic, so that the holder of the plastic token could tear it apart to get at the private key.

A strip of mylar would probably due. Makes me think of fortune cookies.

[marcus_of_augustus]

By the way...  Any thoughts on this item?

http://www.chrismartenson.com/forum/defendant-convicted-minting-his-own-currency/55031

Another case for using paper, I should think.

Plastic casino chip like tokens would work well too, and could use RFID tags inbedded into the plastic to hold the public key.  And even the private key could be micro-etched onto a thin piece of metal imbedded into the plastic, so that the holder of the plastic token could tear it apart to get at the private key.

Or like those scratch and win Instant Lotto cards or some mobile recharge cars ... underneath is the address that contains the denomination of BTC printed on the front. While the scratch is intact it is tradeable.

[marcus_of_augustus]

moa, I followed your link and read, but I don't see the connection to what we're talking about. The real bill doctrine seems to be that, if a note is in principle payable on demand, then its issuer can issue as many notes as it wants as long as those notes are balanced by assets accrued.

An example would be if Big Bank Inc. promised to redeem its notes in bitcoin, and perhaps even kept some bitcoins on hand for redemption purposes, but also disbursed loans in note form without holding enough bitcoins to cover them. The bank would then book the loan itself as an asset. In case of a run, the bank would either call in accounts early, liquidate assets, or borrow against its accounts receivable.

This system works, sort of, but becomes unstable when the note/reserve ratio grows too high. The danger is simply that assets can be lost, particularly assets that are only accrued and not yet received. In the above example, some debtors will default and their loans will be written off, reducing the bank's assets while leaving its liabilities untouched. Charging interest on loans provides some protection against this, but given enough time the bank is quite likely to have a long run of bad luck and become insolvent.

Anyway, that's not the sort of thing I was planning. I'm interested in a 100% reserve kept safe by multiple offsite backups and strong encryption---the most mucking about I'd allow for is a sort of very short-term bond system wherein the bank might issue notes payable at the end of the month, and secure the bitcoins before then, in the interest of fixing very short-term liquidity problems. As long as this was stated up front on the notes I don't think it would be a serious problem.

As for expiration dates, you people are far more accepting of the idea than I would have guessed. Of course they'd have to be both prominently written and easy to predict---perhaps notes could be released in batches that expire at the end of a calendar year, with "VOID AFTER DECEMBER 2013" written in large print on the reverse. The revenue from unredeemed notes would easily make up the printing costs--if we assume each note costs 0.1 BTC to print, a single unredeemed 50 BTC note would cover the cost of 500 notes printed. Given the amount of cash destroyed in every year, not to mention the number of people who can't manage to mail in a $100 rebate form, issuing cash could be very profitable indeed.

Yes, it is not clear from the Wiki how Real Bills would be related to this ... here is a better link. There was a big controversy in academic economic circles about it .... credit money, like BTC, lends itself naturally to true real bills of exchange.
http://www.thedailybell.com/1237/Real-Bills-Revisited.html

[Ian Maxwell]

A single-piece plastic token containing a private key inside.... good idea! They'd still have to be hard to counterfeit, so that you'd know the token really was issued by a trustworthy source (else you might be unpleasantly surprised when you try to break the token open and redeem it).

Another low-cost idea: those security mailers that are used to send out debit card PINs and the like. Put a private address inside, or a QR code for a transaction. Making this simple enough for an average user might require some additions to the client software, but the average user would probably be satisfied bringing the note to a local bank or computer-savvy friend.

No high technology is needed to encode the private key---a simple text printout is good enough.

I point out that I'm still nervous about these ideas. Speaking for myself as a potential guarantor, if I'm going to be held responsible for other peoples' bitcoins, I want to be in control of how they leave my possession. If I issue self-redeeming notes I will have to disclaim responsibility for missing deposits.

[MoonShadow]

A single-piece plastic token containing a private key inside.... good idea! They'd still have to be hard to counterfeit, so that you'd know the token really was issued by a trustworthy source (else you might be unpleasantly surprised when you try to break the token open and redeem it).

Which is why I mentioned an RFID chip as well, which could contain the address that the private key (keypair) hidden inside refers to.  So anyone with an RFID reader could check the address against a blockchain to see if the address still had the coins.

[Bruce Wagner]

" ...anyone with an RFID reader... "

I'm trying to count how many people I know who carry around an RFID reader....  

These ideas are great...  Very creative...  And very technical....

I was looking for a much simpler idea though.   Like a simple handwritten IOU.    ....backed by Bitcoin.

Paper is fine.   With an expiration date, and small denominations...., so that it's not practical, nor profitable enough, to interest counterfeiters.

As I said, I don't see such a form of "currency" being used in commerce really.   I see it used at cocktail parties and brunches...  where, when the topic of Bitcoin comes up, a person can pull one out of his wallet..... and say, "Here... Let me pay for lunch.  This is a 20 Bitcoin note."

.....and the note itself would contain printed instructions on how to redeem it.... including the web site to go to to learn all the details about Bitcoin.

.....thus being a convenient way to gift a few Bitcoins to someone... at the same time as you are informing them about what Bitcoin is.

Like a simple Bitcoin "business card"... that happens to have real value built-in to it.

Each printed batch could expire after 1 year, or 3 years, or 5 years (which would make sense?)...   Prominently on the front it should say, "This certificate expires on January 1, 2014" ....explaining that it must be redeemed for real Bitcoins, or replaced with a new certificate, prior to that date.

They could come in only one  denomination:     1 Bitcoin

....or two denominations:     1 Bitcoin     and     10 Bitcoins

....or three denominations:     1 Bitcoin     and     10 Bitcoins     and     20 Bitcoins

They could be purchased for their face value, and redeemed at any time for their face value.

Once Bitcoin has become so mainstream... and everyone on Earth has a Bitcoin smartphone app or the equivalent...  the Paper Bitcoin will no longer be needed, and they can stop being issued.... They can all simply be redeemed as they come in... until there are no more.   It can end naturally, from attrition.

From what I understand, such paper certificates printed on custom-designed security paper could cost as little as 25 cents each to print (and up... depending on how many "layers of security you want to include in the printing process).

For that matter, if we spent $0.25 per item for the 1 Bitcoin denomination paper....   At the same ratio of cost/value...  we could spend $2.50 per item for the 10 Bitcoin denomination paper....  And $5.00 per item for the 20 Bitcoin paper...    if that makes sense to do.

[NghtRppr]

Or like those scratch and win Instant Lotto cards or some mobile recharge cars ... underneath is the address that contains the denomination of BTC printed on the front. While the scratch is intact it is tradeable.

I'll be doing something like that for the event I'm planning next week (See: http://bitcointalk.org/index.php?topic=6202.0)

[Rena]

I like the idea of physical Bitcoins, but I think paper isn't going to be very feasible. No matter what system you come up with to try to secure the keys, someone will find a way around it. It is like DRM in a sense: you're trying to stop "the bad guy" from copying information (the private key), while still letting "the good guy" access it. Difference is instead of "the bad guy" being someone who wants to copy music they paid for, it's someone who wants to copy a key before passing now-useless cash on to some poor sap.
Never underestimate the resources, smarts, and time crooks have to dedicate to their work, especially when it involves essentially stealing money (from the sucker they pass the bill to after copying it). There are a few of us and thousands of them who'd love to be able to give themselves free money.
That's not to say I don't think we should even consider some kind of physical/printed currency. I just don't think it'll be as simple to prevent fraud as some seem to think.

What I think would be more feasible and useful is using SD cards and USB sticks as coins and wallets. These days you can get 32GB of each for under $100. For use as coins you'd want not one large card but many small ones (even 1MB should be plenty) - probably everyone has a few laying around, and for such small sizes I'd imagine they'd cost only a few cents each.

For coins, you'd put a private key (or a few) on a card and hand it out. To redeem the coin you put it into your PC and copy the key into your client. SD cards are roughly the size of a coin and just about everyone has a reader for them (and if not they're cheap and have many uses) so this works nicely. MicroSD is a bit small (easily lost) but has some advantages like being usable in modern phones; keeping them in the plastic case they come in could help with the size issue.

For wallets, you'd put a few coins into a wallet file stored on a USB stick. You could hand those out too (like "bills", being physically larger than SD cards) or use them like a bank card - put the stick in, transfer a few coins.

Advantages of this are that you'd be using ordinary SD cards and USB sticks, that are too small in capacity to be of much other use, can be "refilled", and can hold other data besides just the coins. So you could include some notes or media with a payment. For example when paying your bills, just send in a card/stick containing the balance and a text file holding your account number. (Granted if you can pay bills in bitcoins, you'd probably do so over the Internet, but anyway...)

Obvious problems:
1) People can still easily copy the coins and then hand them out again.
2) A merchant can copy your entire wallet when you put the USB stick in to pay.
3) While small-capacity cards would presumably be cheap, nobody sells them anymore.
4) Being given an SD card or USB stick, you have no way to know if it even has any coins on it.

#3 I think is the big thing here. While you can walk into your favourite overpriced electronics store and buy a 32GB card for not much, you can't buy 32768 1MB cards at all. Nobody makes 1MB cards anymore.
What you'd have to do is start up a small business selling small cards/sticks for just this purpose. I imagine you could convince a manufacturer in Asia to make you a few thousand small ones for not too much, which could even be stamped with the Bitcoin logo. You earn back the cost by starting up an exchange; someone sends you some amount of money (plus a few cents to cover the cost of the card and postage), you send back a card with that amount on it.

Now, if you already have these cards being manufactured for you, you can go on to add some security features. Say, reading the card destroys it, or the card comes encased in something similar to their plastic cases which must be destroyed to get at the card itself (so you know a card not in such a case is no longer valid). Those ideas kill reusability, but I'm not coming up with any ideas that don't. Ultimately they'd be more like checks than coins, and nothing stops someone from writing you a bum check either.

For "wallet" USB sticks, the most secure thing to do would just be to keep only a little in it at a time, so that anyone who copies it won't get much. Of course that isn't very convenient. What you might have is a stick that unfolds to expose a simple numeric display and keypad, where you type in a balance, then press OK, and it allows only that much to be taken out. One way to do this would be to make "change" - store several keys worth 0.5BTC, 1BTC, 5BTC, etc, and it passes on to the reader only enough keys to make that balance (rounding up if necessary), just like you'd give a cashier only enough coins to make the balance (but if you don't have any pennies maybe giving a nickel to cover the last 3 cents).
Having such intelligence in the stick itself would of course increase its cost, but you'd only need one - you wouldn't be handing these out to people like you would with coins; they'd function more like a bank card.
You could eliminate the need for a lot of complexity in the design by just having it emulate an ordinary removable disk, with one partition where you can store files like any ordinary disk, and one reserved for the coin keys. When you hit OK, the appropriate keys are readable from the raw partition (no filesystem) and removed from memory on read. Writing a program to handle this on a PC would be dead simple. The device could also be powered by the USB port itself, reducing a lot of physical complexity.


I think no matter what you do, it's going to be somewhere between difficult and impossible to make physical bitcoins that don't carry the risk that they've already been digitally spent (or if you use SD cards, that they don't actually contain coins at all). It boils down to being given an object which is said to have value, but which becomes worthless through an action that can be done without physical access to the object. You have to trust that they won't do that, because there's really not much you can do to prevent it. I also think the future of Bitcoin for in-person transactions is in smartphone apps, not distributable tokens. But if you could make tokens and smart USB sticks work, that'd be pretty damn cool.

[fergalish]

I was looking for a much simpler idea though.   Like a simple handwritten IOU.    ....backed by Bitcoin.

Unless there was some security built into the paper system, I would never accept it, *except* if I was accepting it from the (trusted) issuer.  Even if my most excellent trusted friend tried to give me one, I wouldn't accept it because, even though he's acting in good faith, the note might have already been cashed in (or copied, whatever) by some nasty previous holder.  Also, I wouldn't accept a token that couldn't be automatically redeemed - otherwise the other party to my transaction could give me the token, I'd check the (visible) address to see that it was still valuable, but then the other party could redeem it, from a copy, after 10 minutes.  I'd want to secure the funds in my own wallet immediately - for me, that's what the transaction is: putting funds into my wallet.

...it's someone who wants to copy a key before passing now-useless cash on to some poor sap.
<snip>
I think no matter what you do, it's going to be somewhere between difficult and impossible to make physical bitcoins that don't carry the risk that they've already been digitally spen. It boils down to being given an object which is said to have value, but which becomes worthless through an action that can be done without physical access to the object.

The token must be visibly destroyed for redemption.  But you can always check that the coins haven't been spent by checking the visible address against the blockchain.  So any attacker only has time to cheat you from the moment you accept the token to the time you try to redeem it.  This time should be made as short as possible, therefore, automatically redeemable tokens, NOT requiring you to return them to the issuer.

[Bruce Wagner]

Just for the record...

My concept would NOT involve Bitcoin keys at all.  It would simply involve a paper currency on high-security paper (or similar material) with lots of anti-counterfeiting security built-in --- very similar to the drivers license in your wallet.... or the vehicle registration in your glove box.... or the state ID card...  or the dollar bill in your wallet.

It would have a serial number, but no Bitcoin data.    It would be denominated in Bitcoin, and it would be backed 100% by Bitcoin.    But it would require NO computer or electronics at all.    It could be passed hand to hand...   and redeemed at any time for real Bitcoin....  by the issuer.

Obviously, this would only work with a "trusted issuer".

However, depending on who the issuer is....  I think I'd rather trust ONE single "trusted issuer"...  than trust every person who handles the paper.

With this simple system, there's no way of defrauding it ---- except through counterfeiting.   This drastically reduces the risk.   It also moves more of the risk over to the issuer.

With high security forms of printing, etching, etc., etc. in use today (just look closely at your passport), the risk of counterfeiting can be reduced to almost nothing.   Especially when combined with a reasonable expiration date..... and low denominations....   and the fact that most of this currency would remain within the Bitcoin-promoting community.   It won't be very widespread use.    The potential profit a counterfeiter could make would be so small that it wouldn't really be worth his time.   It would be like breaking in to your house to steal a donut and a glass of milk.

[ Alternatively, they could be made for single-use.... like Travelers Checks.   The purchaser could buy one, sign it on one line.   Then, when paying someone, he could sign it again on another line.   The unique code number could even be "called in" over the telephone to verify it's validity... and to verify that it has not been used before (much like a Groupon coupon).   You can print as many copies of a Groupon coupon as you want, but the unique code on it can only be used ONCE.   After it has been used, it is void from then on, and it's payable only to the first claimant.    With such a system, the code numbers on the "coupon" must be kept secret (like a password), and they can only be used for one transaction, and with this method... there's now the added overhead of a "call center" infrastructure... needed to give verifications. ]

I still think the best way is the simplest.    A paper "receipt" for 1 Bitcoin or 10 Bitcoins or 20 Bitcoins.....  simply backed for its face value by the trusted issuer....  and that's it.

I guess the problem is...   After being burned by so many central banks throughout history...  Do we trust ANYONE with that control?

As for the hidden private key forms of a currency, I think there are several in development already...  So I have no doubt that that concept will be readily available soon.

I'd like to see the "paper currency" that operates independently of the Bitcoin network, yet is backed 100% by Bitcoin.... become available as an option too.   Not everyone in the world has a computer.   And even among those that do, not everyone understands the first thing about a "private key" or a "block chain"... much less how to verify the ownership of specific Bitcoins based on that data.   I don't even know how to do that.    I'm looking for an alternative that would also work for the common man on the street, who may not even have a computer or a smartphone....  But he may wanna "buy some Bitcoins" because he heard that the price is going up!    .....or whatever.

[florian]

In the end everyone is used to spend money with plastic cards. Implementing Bitcoin on top of a smartcard should be possible. Just put the key pair on it and implement a signing action. You'd have to trust the card reader to display the correct amount they will take from the card ... but hey ... you do this today and all the time.

[marcus_of_augustus]

Limited edition high quality printings may well continue to have numismatic value even after the BTC represented are redeemed.

Just think of first edition superman comics .... first ever anything that does not die out only gains in value, enhanced by rarity over time. It's all money in the end.

[Bruce Wagner]

True...
Very interesting.
Well, the samples should be arriving here via FedEx within about 4 hours....
I'll let you know....

PS - "The Bitcoin Show" is now available on OnlyOneTV.com | global television network http://goo.gl/wBdBi

[silvercardbank]

The technology of the  bit coin system is in place already ! To be secure against counterfeiting,and inflation by the fed,it cant be taxed and you don't have to tust anyone that you do not know because it must be genuine to be in the system..  To make bit coins in to something physical to be spent in any shop is the same as taking your bitcoins out of the  secure system and converting them into cash or converting them onto your credit card.
that system is already in place !

The only problem with that side of the system in the outside world is that it is controlled by the banksters and not the bit coin community ( the people )

The the only useful purpose  physical bit coin could have, would be to  introduce others and get them to use it.   Use it directly with other bitcoin users going around the banksters controlled system that we have.

if a local store owner accepts it a payment he will not need to use the visa /matercard reader to take payment, therefore avoiding the outrages charges of the banks,....  is this not the point of bit coin ?

 Having a fair and just system .. money for the people controlled by the people .?

what bruce was saying about keeping it simple.... , like writing a simple i owe you works , but a fancy printed iou used as an advertizing tool for bit coin could be much better.

They should be considered to have no value once outside the system, the only value they should have in them is what you personaly attach to it when you hand it over.
For example:

  here is a token or note that i owe you a certain value... introduce the person to this new system.
     Once they are on the system you keep your promise and pay in any currency you like on any system they choose.. hopefully bitcoin and become another member of the community.

when the people accept bit coin as payment, control of the system by banksters will start to weaken and slip while the bitcoin community grows stronger and develops their own  technology to create there own bit coin readers at point of sale.

It,s all about who has control, the many or the few !.

I think that whatever physical systems of bitcoin that are developed, they should all bear this in mind.
 as whoever controls the system control's you.

those in control would love to see us all paying with bitcoin if they still have control of the charges you will incur every time you use your card or phone to buy anything. They are probably pushing for this also.. what a great one world currency !

You think it - you build it - you maintain it - they sell it - you lose !


     

[byronbb]

Bitcoins are already physical in the sense that wallet.dat is vulnerable to loss or theft.

[dishwara]

The moment Bitcoin gets physical, it will become vulnerable. Any physical form needs some one to create & it is HARDWARE.
Satoshi Nakamoto, now Gavin working on SOFTWARE. Since software, he create & then everyone copies it.
Hardware or physical has to be created every single piece. Then some one will have to create & that some one WILL CONTROL.
So far, the trust worthy person in bitcoin is Gavin & he can't create any physical form of bitcoin ALONE.
If he adds friends/trust people with himself to create physical, there is NO guarantee that friends/trust people will be always trusty.
If they take control from Gavin then bitcoin will be ruled by some one, like bank, not by people.

[dishwara]

Anything wrong in my post?
suddenly everyone silent.

[Ian Maxwell]

Nothing wrong with the post, I just don't see much to respond to in it. There will be some vulnerabilities with paper notes, just like there are with, say, checks---but most people decide that the convenience makes up for the risk.

Is anyone planning on buying or selling wares for bitcoins at the conference in August? If so, I have some ideas for a sort of "clearing house" that would make this easier.