Also, things like DVB tuners are not exactly cheap enough to be integrated into many devices (though FM receivers, which may be used in the future, are).
If the payment terminal used an SPV-like technology, the attacker would have to have a tremendous amount of computing power. This attack is not feasible, especially considering the relatively small reward of fooling an ATM or a parking meter.
Are there any such chips other than the Broadcom chip that was announced last year?
In this case, there's a single communications channel that could be spoofed by anyone with a transmitter powerful enough to drown out the legitimate signal.
You could stop sending new blocks, but that would alarm the endpoint because it will be stuck at block 100 (in our example).
The Proof-of-work scheme is pretty innovative.
As noted in the article (under the "technology" page), signing is planned but not yet implemented.
> Also, things like DVB tuners are not exactly cheap enough to be integrated into many devices (though FM receivers, which may be used in the future, are).
What kind of devices are you thinking of? It seems to me that the most useful applications of this system would be for vending machines. A $10 DVB-T demodulator (at scale they can be had much cheaper than that) is a rounding error in the cost of those devices.
Cryptocurrency's design targeted the libertarian dystopia related to the interdependent nature (and potential abuse) of governments and their currencies. Given that the dystopian context doesn't exist strongly enough, other options will continue to have advantages within the current context.
You're more likely to show benefits with this when you can provide oppressed peoples' crypto-wallets with balances that can be converted into subversive tools. This, of course, will gain more of certain types of attention than a young currency could want.
Paying for parking is easy as it is. Same with paying to wash clothes. If you can't get cities and coin-op owners to upgrade to card swipe technology, good luck with selling them on immature digi-currencies.
Cryptocurrency needs to think less about catching up in various verticals and more on creating the killer value app... and the problem is nobody is seeing big $'s around the things that today's currency transfer technology has trouble with. We're on the cusp of IoT. Internetless internet-based currency?
Now sending back transactions to the network is not covered, but can be done by using SMS or a small radio link to a local node. A bitcoin transaction is only about 64 bytes (!) so even a DTMF call or SMS should work fine.
A transaction send would look like this (normal TXid, in hex)
There are mobile payment applications already, but they are doing it using centralized service and they need make deals with payment agents. With Kryptoradio it is possible to receive payments without any extra middlemen.
The proof-of-work blockchain transmission means it's the real and proper blockchain and is valid.
That's unfortunately not sufficient at modern transaction rates. Is there any reason you chose DTMF in particular?
It is only at the stage of a gimmick, or a proof of concept, but if the broadcast service could be relied upon long term, then it might greatly reduce the bandwidth and connectivity costs for simple Bitcoin-enabled devices.
It's misleading to think of it as only a one-way connection, because a user naturally creates a two-way channel.
Imagine a situation where a user sends a payment to the blockchain, via mobile internet, which is then picked up by the device. That is a de facto two-way connection. The user's phone (or whatever) would communicate with the device by a local area connection, such as Wifi, QR code, Bluetooth, even a typed code etc.
Obviously, devices could also have a low bandwidth uplink connection, such as 3g, but it's interesting to think about how it might still be useful with only a 1-way connection. It depends somewhat on the rate and structure of the blockchain data transmission.
This is a fundamental misunderstanding people have about Bitcoin.
A bitcoin before a block confirmation ~ A credit card before 180 days.
There is a small possibility of "undoing" a transaction before a block confirmation, just like there is a small possibility of a customer doing a credit card chargeback before the credit card payment clears. However, it's a pain in the ass (even moreso with Bitcoin), isn't reliable with Bitcoin, and almost no one ever does it.
For small transactions like buying soda from a vending machine, waiting 2 seconds for the transaction to propagate is more than enough.
The only time I would ever wait for a block confirmation is if I was doing a transaction in the thousands of dollars range.
PS: A 51% attack is only needed to counter confirmed transactions unconfirmed transactions have little protection and take a while to get confirmed.
But that's different from a double-spend, which is reversing a tx that already has 1+ confirmation, through a chain reorganization.
The economics and technicalities of this are analyzed extensively in the latest Ethereum blog post https://blog.ethereum.org/2014/07/11/toward-a-12-second-bloc...
That might help, but this is an issue which can be addressed after the pilot starts.
Distribute valuable information (mined blocks and verified transactions) with a nearly constant cost in relation to the recipients.
 I estimated. http://blockchain.info/charts/blocks-size