Subject: Re: [Bitcoin-development] Paper Currency

From: Alex Kotenko <[email-masked]>
Date: Mon, 19 May 2014 11:26:35 +0100

Practically I would approach it from a different angle. We need to make
sure that notes we're accepting are still loaded, but assuming it's NFC
enabled this is still quite easy for the user and is an acceptable
usability drawback.
Then what we need to make sure is that when someone is redeeming the notes
- he has control over physical object itself, ideally for a period of time.

​With some active powered electronics in place it would be easy, but how do
we do it without anything active in place? ​

Best regards,
Alex Kotenko

2014-05-18 21:10 GMT+01:00 Natanael <[email-masked]>:

> The problem with not involving any electronics is that somebody needs to
> generate a recoverable private key that we have to trust haven't recovered
> the private key.
>
> The only plausible solution is multisignature P2SH addresses where you
> trust several independent entities to not collude instead, where you
> combine their paper notes into one piece. And then you still don't know if
> all the private keys are recoverable to you (failed print?).
>
> - Sent from my phone
> Den 18 maj 2014 20:48 skrev "Alex Kotenko" <[email-masked]>:
>
> Erm, few things here.
>> ​- I can't see really how to embed electronics capable to run an SPV
>> cli​ent into printed paper. I know that passive NFC tags can be printed on
>> paper, but not actual chips and/or power modules. So we are talking about a
>> completely different things here.
>> - even with paper notes printed proprietarily by some business the notes
>> itself still can have routes for independent blockchain-based verification,
>> and you won't need to trust anybody to test it. You will have to trust
>> security of the notes itself, but this is same as when you trust the phone
>> manufacturer when you're putting your bitcoin wallet on it.
>>
>> ​So really I see ​only issues of technical security in here, and this is
>> the problem I'm seeking solutions for.
>>
>>
>> Best regards,
>> Alex Kotenko
>>
>>
>> 2014-05-18 14:50 GMT+01:00 Natanael <[email-masked]>:
>>
>>> Now you are talking about Trusted Platform Modules. Like smartcards,
>>> actually. Devices that won't leak their keys but let the holder spend the
>>> coins. It could even have it's own simple SPV wallet client to make it
>>> easier to handle. And they'd use the attestation features provided by the
>>> TPM to prove the software it's unmodified top the current holder.
>>>
>>> But then you still have to trust the manufacturer of the device, and you
>>> have to trust it has no exploitable side channels.
>>>
>>> - Sent from my phone
>>> Den 18 maj 2014 13:52 skrev "Alex Kotenko" <[email-masked]>:
>>> ​
>>>
>>