Originally posted this in the Newbies forum, probably not the best place, it fell off rather quickly.

https://bitcointalk.org/index.php?topic=232971.0

Reposting here, after some refinement.

Something I wanted to make for folks to try out at the Bitcoin conference that was in San Jose in May, but logistics and other factors didn't quite come together in time.

A pinball machine that takes Bitcoin....

I have some pinball machines, as do friends of mine.  An appropriately themed game would be one of the newer, better games: Tron

The game would be set up in a public area, for all to see.  Instead of quarters, I'd print out a barcode and attach it to the front of the game.  Pay to that address and the game would credit up, and then you get to play it.

The hardware would be straightforward.  A little embedded Linux ARM board, running the Bitcoin client.  A large SD card would have plenty of room for the blockchain and the rest of the Linux environment.  The board would have at least one GPIO output, that my software could control.  A little custom circuit would have to be made, using a relay, isolated, to use the GPIO to temporarily close a switch that is normally open, so that the pinball machine can be coined up.  To run the Bitcoin protocol, the Linux board would have an Internet connection via cellular modem.

The advantage of the little board running the Bitcoin protocol itself, is that it would be more self-sufficient.  An alternative is to have it be merely a slave, connecting to another computer somewhere else, and then the only time the cellular modem would need to be used would be when it was actually time to credit up the game.  This has the advantage of requiring much less expensive cellular data, however, then the game is slaved to that other computer, and if that link is lost, players will feel ripped off because they'd pay the Bitcoin but receive no game play!

Wherever it runs, it should be trivial to write a little daemon that continuously monitors a particular Bitcoin address, and detects incoming payments to that address.  Since the game would be something of low value (BTC 0.01 or BTC 0.005 per play, I'm thinking), and the player is waiting immediately to play, and the whole thing is a proof of concept anyway, I would feel comfortable accepting payments with zero confirmations.  There is a risk of double-spending, sure, but perhaps this could be mitigated by monitoring other points in the Bitcoin network (perhaps look up each transaction on blockchain.info or similar service, to detect double-spending attempts).  Since players are anonymous, I wouldn't need to care about the source of the funds, or trying to match them up with an identity.  Somebody halfway around the world could make a payment, causing the game to seemingly add credits to itself out of thin air

Since it would only be accepting payments, and not sending them out, the device need not have the address in its wallet.  This gives it more security, since if somebody breaks into the game and swipes my board, all that is lost is the value of the hardware, no Bitcoin would be lost.

The only disadvantage of this design is that it uses the Bitcoin protocol directly, and the payment amounts are small, so the transaction fee becomes a factor, and it seems kind of silly to have each little game stay on the blockchain for all time.  However, by using Bitcoin directly, instead of a middleman service, it becomes available to all players as an impulse buy, without anybody having to register and fund first at a middleman service.

So, anybody done this already?  Wonder if there's anybody else in the Bitcoin community who is into pinball.  The same concept applies to any other arcade game or amusement device, as well.  Vending machines could also be used, but there'd be a conversion factor to take into account, as the vending product would probably still have to be bought with fiat.

Josh

Interesting.

5430 Satoshis does seem like a magic number.  Any insight as to how it was derived?  The release notes just says that's the amount, without explaining why, as if the number just came down on a stone tablet from the sky.

I'm glad to see the lower minimum TX fee.  I think it should be even lower.  The blocks aren't maxing out yet, at 1MB/block.  There's still plenty of headroom to accept more transactions.

Something I wanted to make for folks to try out at the Bitcoin conference, but time and other factors didn't quite come together in time.

A pinball machine that takes Bitcoin....

I have some pinball machines, as do friends of mine.  An appropriately themed game would be one of the newer, better games: Tron.

The game would be set up in a public area, for all to see.  Instead of quarters, I'd print out a barcode and attach it to the front of the game.  Pay to that address and the game would credit up, and then you get to play it.

The hardware would be straightforward.  A little embedded Linux ARM board, running the Bitcoin client.  A large SD card would have plenty of room for the blockchain and the rest of the Linux environment.  The board would have at least one GPIO output, that my software could control.  A little custom circuit would have to be made, using a relay, isolated, to use the GPIO to temporarily close a switch that is normally open, so that the pinball machine can be coined up.  To run the Bitcoin protocol, the Linux board would have an Internet connection via cellular modem.

It should be trivial to write a little daemon that continuously monitors a particular Bitcoin address, and detects incoming payments to that address.  Since the game would be something of low value (BTC 0.01 or BTC 0.005 per play, I'm thinking), and the player is waiting immediately to play, and the whole thing is a proof of concept anyway, I would feel comfortable accepting payments with zero confirmations.  Since players are anonymous, I wouldn't need to care about the source of the funds, or trying to match them up with an identity.  Somebody halfway around the world could make a payment, causing the game to seemingly add credits to itself out of thin air

Since it would only be accepting payments, and not sending them out, the device need not have the address in its wallet.  This gives it more security, since if somebody breaks into the game and swipes my board, all that is lost is the value of the hardware, no Bitcoin would be lost.

The only disadvantage of this design is that it uses the Bitcoin protocol directly, and the payment amounts are small, so the transaction fee becomes a factor, and it seems kind of silly to have each little game stay on the blockchain for all time.  However, by using Bitcoin directly, instead of a middleman service, it becomes available to all players as an impulse buy, without anybody having to register and fund first at a middleman service.

So, anybody done this already?  Wonder if there's anybody else in the Bitcoin community who is into pinball.  The same concept applies to any other arcade game or amusement device, as well.  Vending machines could also be used, but there'd be a conversion factor to take into account, as the vending product would probably still have to be bought with fiat.

Josh

I've been running 0.8.1 for a while, it's tried and true.

Should I upgrade to 0.8.2?

What advantages and disadvantages does it bring?

I'm curious, because even though 0.8.2 came out recently, I did "getpeerinfo" in my client and find that the vast majority of other nodes that I'm connected to are still running 0.8.1.  Are people holding back for a reason?

Thanks!

Josh

Krellan; 1; 2.04236; 15NN5cJJsSLGuJ4UHoYRwbLMNyLYpRV7PB

PM with shipping information (signed) has been sent!

Edit: Sent in 2 transactions, because of underpayment earlier, sorry about that.

2.04236 from 15NN5cJJsSLGuJ4UHoYRwbLMNyLYpRV7PB
0.20944 from 1EfVc89NxnLiFVoHTMvkPJ6xae6TBHiDyn

2.25180 total

Nice!  Glad I saw this.  Will send in payment for 1 unit ASAP.

Anybody else a fan of the "Hikaru No Go" anime/manga?

I see a lot of parallels between Satoshi and Sai....

It would take a lot of work, that's true, but there's nothing really stopping it from being done.  Just wondering if anybody's done it already

Hi there.

Anybody remember the old intrade.com site?  It was very useful during the 2008 and 2012 elections in the USA.  However, it was taken down.  An obvious idea is to make a clone of that site, but now using Bitcoin instead of "traditional money", to avoid the financial/bank problems that Intrade ran into.

Does such a site exist already?

I found betsofbitco.in which lets you place yes/no predictions, however, it isn't based on a contract that can be bought/sold like Intrade was.  The big advantage of Intrade was that it gave everybody an accurate percentage prediction on whether or not something would be coming true in the future, based on the price of that contract, so people could use it as a crowdsourced prediction tool.

The contracts paid out at 100% if true, 0% if false, and before the outcome of the event was known, it was floated on an open exchange, to trade freely, by posting bids/asks within that range.  Speculators could buy or sell contracts.  Short selling was also easily handled without running into margin problems, because unlike a traditional stock market, the maximum risk of these contracts is known, as the value can never go above 100%.

If a clone of Intrade doesn't already exist in the "Bitcoin world", well, that's your market opportunity!

Is anybody working on such a site?

Josh

Nice, glad I could test that feature for you!

I (nervously) waited around, and good news, it reopened again, right about that time.  Now I can buy my share and go to bed

Great exchange, but I made a rookie mistake.  I got my PIN locked.  Reason is, I got confused as to whether or not certain PIN fields require the chosen PIN when creating the account at btct.co (4 digit PIN) vs. using the PIN number obtained from Google Authenticator (6 digit PIN).  Evidently I filled in the wrong PIN once too many times.

Now every transaction attempt gives me "Repeated Incorrect PIN -- PIN Transactions Temporarily Locked."

How long is this lockout for?

Thanks!

Nice!  I didn't know about "Coin Control".  That gives me something to search for.

That's a great reason.  That would imply that a backup must be taken at least once every 100 transactions, otherwise there is a risk of loss if something happens to your installation, right?


Would it be useful to anybody else if these change addresses were also displayed, perhaps with the current balance of each address?  That might be useful for truly seeing how your holdings are spread across your addresses.

Also, it might be useful if the amount of pregenerated addresses could be set to something other than 100.  If each transaction is going to consume an address, for example, then it might be useful to set this to 1000 or something like that, to guarantee a backup will be good for a long time.  Conversely, if the user wants a smaller wallet, and doesn't plan to spend very many transactions before taking another backup, this could be lowered.


Would this problem go away if the Bitcoin client were made aware of every address within both wallets, including change addresses, and merged each list together so that all addresses were unified into a single wallet, including the private key for each address?  It seems that a "Merge Wallet" feature would be useful.  It would result in one wallet containing the combined balance of both previous wallets.


Is it possible to control from which address(es) the coins are spent from?  If so, the user could be careful to select different addresses for each outgoing transaction, during the time the installations would be out of sync.  That should solve the problem of double-spending from the same address.

Thanks for the warnings.  They have given me good ideas for adding features to the Bitcoin client in the future, but for now, if I start a second Bitcoin installation, I'll do it from scratch.  I can then easily transfer a balance by paying myself.

Interesting.  The Bitcoin client generates addresses in advance?  I wonder why it does that: non-vanity address generation shouldn't take very long at all.  I thought it generated addresses on the fly, whenever needed.


Thanks.  Does it have to be named exactly "wallet.dat"?  I assume the Bitcoin client will pick it up, when that file is placed in the Bitcoin client's main directory that it manages (not any subdirectories)?


Interesting.  I didn't mean for it to remain in continuous synchronization, but rather, to use the wallet.dat file from one installation to bootstrap another installation.

Are the displayed addresses in my Bitcoin wallet all it takes to represent my holdings?  Or, are there more addresses than what is displayed?  All the Bitcoin client displays is my total balance across all addresses, it doesn't let me break it down by address (however I verified a few addresses against what blockchain.info displays, and it seems to add up OK).

How would it lose coins, if running multiple installations?  If the network is consistent, then all of my addresses should have a balance associated with them, and anybody could add them all up to determine my total balance, correct?  Or, is there some magic state associated with each installation?


Ouch.  It would be very useful to be able to see all of these hidden addresses, as well as a way to see balance by address (not just an overall total balance).


Interesting.  I wonder if there would be interest from others in adding this feature, to be done automatically?  An opportunity for a project.  Solving the problem of making it easier to merge wallets, would also make it easier to restore wallets, as doing a merge into an empty wallet is the same thing as doing a restore.

Hoping this isn't the super obvious newbie question that I just overlooked.

I've done "Backup Wallet" in my bitcoin-qt client, it wrote a wallet.dat file just fine.  I repeated that a few times, backing up to various drives and USB sticks.

I noticed the file is rather large for what I thought was just the private keys for my Bitcoin addresses.  What is contained in the wallet file?  Mine was around 300K, which is still very small, but large for just a few private keys.  What else is in the wallet file?

Anyway, my question is, how do I then restore the wallet that I've backed up?  Thinking "Restore Wallet" would be right next to "Backup Wallet" in the menu, it wasn't.

I want to also set up a bitcoin-qt client on another computer, and want them to sync up, so that they both see the same addresses and show my balance.  This will also be a good test of whether or not the wallet.dat file truly does a full restore.  Ideally, the account balance should always match, assuming both computers are fully caught up to the latest blockchain, right?

Also curious: How can I merge two wallets together, in the bitcoin-qt client?  That would also be useful.

Thanks!
Josh

Wow, your post is a great answer!  It's a good concise writeup of how it works.  There's a lot of misinformation out there, and this helps to clear it up.  Wish I had read this in a FAQ somewhere first, it would have saved me from asking some silly questions!

Josh

Nice, thanks for pointing me in the right direction!

Josh

I'm curious, how does the Bitcoin network resolve conflicting transactions?  I looked for this in a FAQ, but couldn't find details on exactly how the network chooses which of two choices to believe, when given conflicting choices.

This could either be done intentionally (flooding others in an effort to induce lag, hacking the Bitcoin client to disable consistency checks, generating false confirmations, intentional double-spending, connecting a large network of your hacked Bitcoin clients in an effort to steal traffic from the existing network, any other ways) or accidentally (connecting to the Test network instead of the real network, running offline for a while then reconnecting later).

Which determines the winner?  How does the network know to discard unwanted transactions, provided that those unwanted transactions are not totaling enough to constitute a 51% attack?

It makes sense that Bitcoin would still be vulnerable to a 51% attack.  A corporation is vulnerable (convince 51% of shareholders to vote your way, or just buy 51% of all shares, and you can appoint yourself CEO and do whatever you want), and a democratic government is vulnerable (convince 51% of voters to vote for you, and you are President).  Evidently that's pretty much how the world works, nothing can really be done about that

Josh

I thought of that as well, but have no proof (and even this is just circumstantial, IP geolocation can put you anywhere, it routinely puts me in another state).

My guess is that they're doing a lot of really good extended burn-in testing to make sure your hardware works correctly

Honestly, they have no rational reason to ship ASIC's now, if they have them.  Since they're one of the few people in the world with a batch of ASIC's, they're probably doing all the mining they can now, because it's very profitable.  If you had something that would put you ahead of the curve, giving you more compute power than everybody else, why would you give it away?  The profit now, from keeping them for your own mining, would outweigh the revenue you would get from selling them.  Therefore, no incentive to sell them.  At best, if it were me, I'd sell only a few at a time, enough to keep people happy that they're getting their orders eventually, but keep most of them for myself.

I can see two things that would motivate them to start shipping their ASIC's: 1) If the difficulty got high enough that even ASIC mining wouldn't be profitable enough to outweigh the revenue from shipping the ASIC's, and/or 2) another different supplier of ASIC's starts selling them to everybody so it's no longer special/unique to have an ASIC relative to everybody else's compute power.

Josh

Nice, thanks for clearing that up!

I think what's happened is a lot of content has been written about Bitcoin in the last few weeks (obviously), some good, some bad, and a lot of people are reading it and getting misconceptions.

Is this all in a FAQ somewhere?  I looked around and read various FAQ's, but didn't see this mentioned.  I rather like your explanation, it clears things up.