Printing bitcoins, an implementation

[netrin]

A similar take on the signing check idea, is to symmetrically encrypt the private key before encoding in QR/Data matrix. Then writing the password on the check 'signs' it. Of course the paper money isn't transferable before 'password signing'.

[Binford 6100]

... you have to make it easy for the village idiot to use ...

might be related (and please do not overthink the following example that i might however compare any parent of any of us to any village type user ...

Quote from: gavinandresen on May 19, 2011, 05:08:27 pm
I think it is important to set expectations; I still wouldn't recommend that my mom use bitcoin for anything just yet, because it is not easy enough to use securely. And the road ahead is likely to be bumpy; there will be technical issues that need fixing, there will be legal questions, there will be price bubbles, and there will be scams. I predict that some company using bitcoins to do something illegal will be caught and prosecuted, and that will be mis-reported as "Bitcoin is illegal."

in the meantime someone is printing bitcoins but for cca 10% of their face value
& you have to trust him/her that you have the only copy of the keys ...

[kstepyra]

If this is one time use paper(private key) - it wont work. Paper consumption around the world will be insane.
And another problem - if someone will see and just take photo of our money - we will lose it.

So we are coming to the beginning  - banks - we will need them to keep bitcoins and get paper edition of them without public/private keys printed in it but:
a) only with security signs like current USD or other money have to prove their validity
b) just with PUBLIC key to check if it is really somewhere in the network, also backed up in one of the central points.

It's not that easy to get it safe.

mine 0.02 btc

[krepta3000]

I'm so confused trying to read this thread.  I really like BitBills, plastic cards containing Bitcoins, very cool concept.

[Narydu]

Very good thread! I read it all and understood half but it is extremly interesting. I do believe that a one time use paper will soon find lot of uses, specially as for gifting. Is there a new thread about this?


Idea1 - where the issuer knows the new holder: There could be a free central colector (not bank) which holds paper transfered bitcoins so as to avoid trusting in each individual user. This collector shall reccord every transaction as individual and save some aditional data as a password to check the validity of the holder. QR eps would be issued to add it were ever you want, recalling this central colector and will ask for the password which will be revealed by the issuer as revealing the signature in the creditcard. Then the coins could be redeemed or change the password for fowarding them to a new holder or send them into a wallet. The system should allow to transfer many different amounts and have a central user control pannel.

Idea2 - the issuer don't knows the new holder: same central colector, QR+password hidden under metal ink. Obviously onetime redeem per paper.

Is this too simple and wrong? Sorry my english please.

[TheBitMan]

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.

Used my Android but a bunch of letters pop up and now I am confused 

[netrin]

I could invision a service whereby I generate key pairs and send them off to be minted.

I generate key pairs on my computer. I then symmetrically encrypt the private key and send them to the print-minting service along with identifying information, perhaps even my photo. The print-mint prints unique bill-notes (with my smiling mug in the center) and sends them back to me. I can then write the passphrase on the bill-notes (either in advance or upon purchase/distribution).

Recipients must trust me or transfer the bitcoins from the bill-note immediately. Recipients must trust the print-mint not to duplicate bill-notes and that counterfeiting is impractical, or again just transfer bitcoins to themselves upon receipt. The print-mint can verify that I have not duplicated the keys (at least with respect to the block chain and the print-mints own public key records).

[TT]

"Therefore, my technique would be inappropriate if I was only given the 32-byte private key. I've got no idea how to actually compute it "

It's all in the CKey class in key.h

CKey::GetPrivKey and CKey::SetPrivKey use the 279-byte DER key.
CKey::GetSecret and CKey::SetSecret use the 32-byte private key.

Look at the satoshi client source code for details on how to call the OpenSSL library.

https://github.com/bitcoin/bitcoin/blob/master/src/key.h