I was thinking of what a scammer would do with the ability to print Bitcoin bills for an in person transaction:
1) Print a bill with a corrupted private key and a real address
2) Keep a copy of the real private key
3) Fund the address
4) Show the person you are paying that the Bitcoin address is funded
5) Walk away with your goods and Bitcoins
6) The victim wont know that the private key is useless until they are online and try and import it
Being able to confirm that the private key actually connects to the address gets you some protection against this.
The other scheme is:
1) Print a bill with a good private key and a real address
2) Import the private key to an online wallet
3) Fund the address
4) Show the person you are paying that the Bitcoin address is funded
5) Right after they see its funded, pretend you are checking a text message, but send the money back to yourself with your phone.
6) Walk away with everything
I'm not sure how to get protection against this one.
Topic: I just made my first Bitcoin ATM withdrawal... 3BTC from my printer. - page 3. (Read 14497 times)
August 10, 2012, 11:44:34 AM
August 10, 2012, 04:07:14 AM
Then of course I'd still need a net connection to check the balance...
But still, is offline private key/address verification possible with out the client?
But still, is offline private key/address verification possible with out the client?
I'm not sure what you mean. Checking that a private key is valid and matches a given public address? This should be possible, but not very useful, since what you'd really be interested in is whether the address holds funds. And even if it did, being offline you could not transfer the funds to a key only you control.
August 10, 2012, 03:46:47 AM
Then of course I'd still need a net connection to check the balance...
But still, is offline private key/address verification possible with out the client?
But still, is offline private key/address verification possible with out the client?
August 10, 2012, 03:11:28 AM
How do you verify that a private key is valid and backs a particular address? Can this be done offline?
Every time I think I completely understand Bitcoin I hit questions like this. I know the client will do it for you, but I'd like to hold up my phone and have is say yes or no to a paper note instantly and without a net connection.
Every time I think I completely understand Bitcoin I hit questions like this. I know the client will do it for you, but I'd like to hold up my phone and have is say yes or no to a paper note instantly and without a net connection.
August 09, 2012, 09:13:52 PM
Yeah I didn't even think of that. It would be nice for it to print the remaining balance on it to make it easier to remember what it's actually still worth. I would love to have a 15.8686493 denomination bill. :-P
August 09, 2012, 08:54:32 PM
The vending machine could also return change to the bill. Or to another BTC address provided by the customer via the QR scanner. No printer needed.
August 09, 2012, 08:48:15 PM
For the bills a bill reader like on vending machines could be modified to read the QR code and import the private key to the store's wallet. Once it is verified the bill could be shredded and recycled. For change they could use a heat printer to spit out a QR code with the remaining balance. It would be awesome if you could incorporate your program into the actual Bitcoin client so you just tell it what denomination bills you want and it would print them out. The client would show your wallet balance and the balance of your printed bills which would be updated when someone claims the private key when you spend a bill.
August 09, 2012, 08:35:41 PM
The problem with self printed bills is always going trust. This is where it would be useful the have trusted third party vendors issuing paper currency, with bitcoins to back the value. Hide the private key under a tamper evident hologram just like the coins. You should be able to get these printed for pennies.
There is nothing wrong with having a central issuer of paper money... the problem is when they have an effect on the value of that money. This would not be the case here.
These self printed bills would be great for use where both parties trust the other.
There is nothing wrong with having a central issuer of paper money... the problem is when they have an effect on the value of that money. This would not be the case here.
These self printed bills would be great for use where both parties trust the other.
No trust required. Verify the bill before accepting...you aren't trusting the bill to be valid, you are verifying the private key is backed by Bitcoins....
August 09, 2012, 08:29:05 PM
I assume it's the private key that's under your finger. Without any additional security measures, how can one be sure that a paper coin is unspent?
The idea with these is that the receiver of a bill scans the private key, immediately moving the funds to another address. The bill can then be discarded.
So stupid... if you NEED INTERNET ACCESS to verify it, then why is it in paper in the first place?
This is only useful for personal offline backup, never to be used for public transfer.
August 09, 2012, 06:06:59 PM
It´s cool!
I would like to use in Brazil.
I would like to use in Brazil.
August 09, 2012, 06:05:00 PM
I have restored the newer version.
Thanks. So the "Denomination" option does not actually do anything yet? I didn't notice any difference in how the bills were printed...
Not on the version I posted - ironically, the only place it prints is on the 16-to-a-page wallets. I was experimenting with cutting the page into 16 little "bills" as an initial test. The next time I update my website though, it will print on the bill.
There is one other place it is used, and that's if you do the "sendmany" export. The idea behind it is the text file is a command line script that funds the wallets in a batch. The funding command needs a denomination so... it is used there.
August 09, 2012, 05:29:10 PM
Looks like my bit cheque still has a balance. Come on people. If you did a search on this forum you will see I used the same passphrase as my last contest. It is ripe for the picking at 119 confirmations.
And we have a winner!
August 09, 2012, 04:12:44 PM
- So only the recipient has internet access in your example: he doesnt want to hand you cash until he sees the private key you are handing over actually has money in it. So he can scan it, hand it back and say it was already empty and runs away. Well he just stole the coins.
By the same token, you could hand him a $20 bill, and he could put it in the register, close the drawer, and then claim it was a $10, or that you gave him nothing at all. Your word against his. It's bad for business. At least where I shop.
Lets pretend for a minute none of that matters, say casascius physical coins have a hidden private key under a hologram... Well if casascius wants to make any profit at all he has to sell them for more than they are worth. This means that if it is at all possible to make a fake, that costs less than it is worth, the market WILL get flooded with fakes.
That could actually happen, but so far it has not. It's just as possible to make real physical bitcoins and make a profit. At DefCon, I walked around wearing a T-shirt that says "I SELL PHYSICAL BITCOINS", and was charging $15 cash for 1BTC coins worth under $9 at MtGox, selling to anyone who'd stop me in the halls. What's better, the $6 I could make consistently by marking up the coin, or the $9 I could scam people for until I was shut down? Meat may be tasty but you don't slaughter a cash cow.
Now there is one scenario that may work: if it costs MORE to produce a physical bitcoin representation than it is worth. In that case you wouldn't want to make a fake that costs more than its worth. But why on earth would anyone do such a thing? They can not make profit and lose money doing it?
The economics of producing holograms are such that it's a big investment to get the holographic master made. On the flip side, if you start scamming people, you'll be left with a bunch of coin materials you can't move because people have caught on to your scam and stopped buying.
In the end, you're right: somebody enterprising could put their efforts into counterfeiting my coins and it would be disappointing. But so far that hasn't happened, and they continue to be a great gift and promotional tool for Bitcoin.
Well there are two different realms here: you are selling these physical bitcoins for novelty and its neat and mostly direct to user sales. Of course you wouldnt sell fakes. But if the whole idea is to have random people trade random "physical bitcoins" all over the world to actually do business, then its not a novelty anymore and real security is very important.
I hate when people fallback to comparing bitcoin thefts to "just like cash". Its a bullshit non-argument. You can't report theft of your intangible digital money to any authority right now, possibly never in the future will it be respected by law enforcement. This is very clear how all the current theives get away scott free. And secondly the BENEFIT of bitcoin is that it is digital, so we should be able to use this to layer hardware security ontop of it so it is better than cash. And lastly, if it is succeptable to ALL of the current problems that cash theft is, plus all the hacking losses, no economy, etc etc... then fuck it why bother.
August 09, 2012, 03:32:55 PM
I have restored the newer version.
Thanks. So the "Denomination" option does not actually do anything yet? I didn't notice any difference in how the bills were printed...
August 09, 2012, 02:38:14 PM
Sorry about that, I didn't realize I accidentally reverted it to an earlier version. I sent an update to my website and didn't realize that an old btcaddress.zip was actually in the update and overwrote what I had posted.
I have restored the newer version.
I have restored the newer version.
August 09, 2012, 02:18:14 PM
Maybe I'm being dense, but, I don't see a Tools menu. At the top there is only a button that says "Wallet Generator" and a button that says "Help." The Wallet Generator button brings up another window that says "Paper Wallet Generator", but it only prints a plain-text list of keys, not the pretty bank note. Did you revert your ZIP file to an older version? The one I downloaded from the above URL didn't include the source either...
I can confirm that the zip file has changed to an older version. August 09, 2012, 01:33:45 PM
OK, Windows users can download my current version of the utility and print Bitcoin notes! It's on the menu under Tools - Paper Wallet Generator.
Binary and source is included. https://casascius.com/btcaddress.zip
Requires .NET Framework 4.0 (which should be present on any recent Windows system). Compiling Source requires Visual Studio 2010 (and probably will work with the free versions of Microsoft's C# compiler)
Note there is a PNG file that contains the graphic used on the notes - you can change this with any other png file with the same aspect ratio.
EDIT: I forgot it also uses the Ubuntu font, and if you don't have this installed, it will probably substitute some other font on your system.
Binary and source is included. https://casascius.com/btcaddress.zip
Requires .NET Framework 4.0 (which should be present on any recent Windows system). Compiling Source requires Visual Studio 2010 (and probably will work with the free versions of Microsoft's C# compiler)
Note there is a PNG file that contains the graphic used on the notes - you can change this with any other png file with the same aspect ratio.
EDIT: I forgot it also uses the Ubuntu font, and if you don't have this installed, it will probably substitute some other font on your system.
Maybe I'm being dense, but, I don't see a Tools menu. At the top there is only a button that says "Wallet Generator" and a button that says "Help." The Wallet Generator button brings up another window that says "Paper Wallet Generator", but it only prints a plain-text list of keys, not the pretty bank note. Did you revert your ZIP file to an older version? The one I downloaded from the above URL didn't include the source either...
August 09, 2012, 11:54:10 AM
I've been experimenting with these via your BitAddress utility. I think they're useful as is for a stylish paper wallet, but here's some suggestions:
I'm already grateful for where they are now, and I've gotten off my duff and made some paper wallets as a result. Thanks a bunch!
-bgc
- The key text is facing the wrong way. I had to fold the bill over to read the public key without the private key showing. If the key text was rotated 180 degrees, then I could cover the private key with my hand while I enter the public key
- The private key QR-Code is a bit large (I think you already commented on this)
- The public key text is a bit too small
- The bill as a whole seems a bit large to me. It might be nice to do something like four to a sheet and just make them a bit smaller.
I'm already grateful for where they are now, and I've gotten off my duff and made some paper wallets as a result. Thanks a bunch!
-bgc
I agree with you on all counts, but might leave the private QR code large just having seen how they wear down in my pocket (or might make it a user selectable option). I'd like to make the bill size an option, and also have different bill colors an option as well. I will probably make it auto-sense the paper size and fill the sheet, right now it is just hard coded to 3 to a page and doesn't even consider the paper size/orientation.
August 09, 2012, 11:32:31 AM
I've been experimenting with these via your BitAddress utility. I think they're useful as is for a stylish paper wallet, but here's some suggestions:
I'm already grateful for where they are now, and I've gotten off my duff and made some paper wallets as a result. Thanks a bunch!
-bgc
- The key text is facing the wrong way. I had to fold the bill over to read the public key without the private key showing. If the key text was rotated 180 degrees, then I could cover the private key with my hand while I enter the public key
- The private key QR-Code is a bit large (I think you already commented on this)
- The public key text is a bit too small
- The bill as a whole seems a bit large to me. It might be nice to do something like four to a sheet and just make them a bit smaller.
I'm already grateful for where they are now, and I've gotten off my duff and made some paper wallets as a result. Thanks a bunch!
-bgc
August 09, 2012, 10:59:53 AM
Looks like my bit cheque still has a balance. Come on people. If you did a search on this forum you will see I used the same passphrase as my last contest. It is ripe for the picking at 119 confirmations.
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