This project had been dormant for a while, but I reused it now for a technology demo on how a Bitcoin payment via NFC might look like. See this thread for more details and a video of the solution: https://bitcointalk.org/index.php?topic=395469.0 .

Hey there! Over the last couple of days I have put together a technology demo of how a point of sale solution using Bitcoin + NFC might look like. Here is the video:

https://www.youtube.com/watch?v=mguRpvf3aMc

And this blog post has some more details: https://www.bridgewalkerapp.com/blog/2014/01/01/bitcoin-nfc-point-of-sale/ . An excerpt:


Feedback much appreciated! :-)

I presented Bridgewalker at the BitcoinKonferenz in Cologne on October 22. There is now a recording available: http://youtu.be/YWKkuQ__N7c . The talk is in German, but I added English subtitles (using YouTube's caption feature) and translated slides.

Scratch that, discussion continues here. ;-)

I have quietly continued working on this, mostly fixing some smaller bugs and increasing stability and robustness of the software system. Some updates:

• I switched from USD to EUR as the counter currency for the time being. As I'm based in Germany and I wanted to focus more on in-person use cases, it makes it more practical for me to prototype it. Sorry to anyone who was relying on USD accounts! I hope to bring back USD and add other currencies at some point in the future.
• Uploaded an old presentation that I gave about green addresses (there called marker addresses): http://www.youtube.com/watch?v=1iLV9zjxHFU . Bridgewalker has support for green addresses, so deposits coming from recognized green addresses are credited instantaneously.
• I put together a video demonstrating the app. It is online at http://www.youtube.com/watch?v=ERVD1xoDT0M - although unfortunately already outdated again. =)
• Implemented preliminary backup functionality for guest accounts.

And Bridgewalker is now also on Twitter: https://www.twitter.com/bridgewalkerapp .

As always: Feedback and comments much appreciated! :-)

I am trying to do something like that with Bridgewalker (https://www.bridgewalkerapp.com/ - "a euro-denominated wallet for the Bitcoin economy"). It currently doesn't have a focus on "social features", but it would be possible to add that. Hit me up if you have any feedback!

My understanding is, that Mt.Gox offers two streaming interfaces: Socket.IO and Websockets. Socket.IO has the option of using Websockets as one of the underlying transport mechanisms, but it still seems to be dealt with differently by Mt.Gox's server. I have long used Socket.IO for Bridgewalker (when I launched it was the only option available, as far as I know) and had lots of issues with it. It was very unreliable and actually got even more unreliable in the last couple of weeks. I have now recently switched to a pure Websocket implemention (using wss://websocket.mtgox.com/mtgox as the endpoint) and so far that seems to be more stable. So I would suggest replacing Socket.IO with a pure Websocket implementation.

Thanks for the kind words! Feel free to get in touch if you want to discuss any kind of partnership - I'm always open to ideas. :-) I guess it's not quite ready for prime time though.

Over the last days I put together a video demonstrating the app. It is now online at http://www.youtube.com/watch?v=ERVD1xoDT0M .

That's a good point. I prefer not to comment on legal aspects at this point, but it's definitely something I have on the radar!


Yes, you do. It's Bitcoin in, Bitcoin out, no other way to fund the wallet. One might imagine this to be used in combination with a Bitcoin ATM: Let the machine scan your Bridgewalker Bitcoin address, put bills in and a few seconds later have the equivalent amount in Bitcoins, exchange rate protected, to be used at a later time.


Thanks! ;-)

Discussion continues here: https://bitcointalk.org/index.php?topic=228535.0

Bridgewalker's website and app got an update and a new strategy in how the idea behind Bridgewalker is presented. Basically it's the counterpart to services like BitPay and Coinbase, which protect merchants from exchange rate risk. Bridgewalker does the same thing for customers. From the website:




  Get the app at: https://www.bridgewalkerapp.com/ !

As always: Feedback and comments much appreciated! :-)

Edit: This topic is locked. The main discussion can be found over here: https://bitcointalk.org/index.php?topic=156943 (11/2013).

Version 0.4 of the app is out now and I have updated the website. I have slightly pivoted in how the idea and the service is presented. The new description reads like this:


Essentially I show your balance in BTC at all times to make it clear that this is really a Bitcoin wallet: Bitcoin in, Bitcoin balance, Bitcoin out. But that Bitcoin balance is adjusted up and down to create that "stable in respect to a counter currency" effect of the original Bridgewalker. It is really just a change in presentation, as the underlying system still works the same. But I'm hoping this presentation might make it easier for people to understand the value proposition and why such a service might be useful in some cases.

What do you guys think? I call it "exchange rate adjusted Bitcoin wallet" - does that term make sense to you? any better alternatives?

Assume a trading bot has the following behavior: You can force it - at a time of your choosing - to buy BTC at spot price. There is a limit on how much it will buy (but within this limit you can specify the amount) and how frequently you can make it buy, as it sort of needs to "recover" first. It does that by selling at spot price sometime later - you cannot influence that part.

Any reliable way of completely eroding this bot's trading funds, given this knowledge?

Quick update: I implemented a workaround to get rid of of the minimum limit of 0.01 BTC. Transactions down to 1 satoshi are now supported.

My impression is, that almost nobody actually bothers to jailbreak their device, even among those people who would be able to do it. So I don't know, it seems to me like that would be a very limited group of people to whom that would be a solution. But I'll keep it in mind!

@BitPay: A new version of the app is out which now completes the support for URI links - i.e. it also works now, when clicking a link somewhere. So that means all "must have"s according to lovebitcoins.org (which, by the way, is down at the moment (?) ) are present. :-)

Yes, good point, I might have to do that, if all else fails. I would just prefer to have real-time updates. Mt.Gox seems to work on a new version of their Socket.IO server, maybe that will improve things.


Aw, thx for pointing that out, I will fix it in next update.


That's definitely something I find very interesting: Go into the next supermarket, buy a Bitcoin gift card denominated in USD ("$20 worth of bitcoins, for $20.25), load that up in Bridgewalker (with the added benefit of checking that you got your money's worth) and then spend it next door on cupcakes or on they other side of the globe on candy from Japan. And as mentioned before, I would consider it a goal to get that complete cycle down to 3 % and lower to be able to compete with credit cards. (At the moment I find all these "Bitcoin has low fees" claims a little bit dishonest. Yes, Bitcoin transactions themselves are fairly cheap, but pretty much anything practical you will do with Bitcoins _today_ will involve some currency conversion steps, which are unfortunately not cheap yet.)

And by the way: Anytime Bitcoin gift cards come up, some people want to have them denominated in BTC. While that seems natural, I don't see how it would be practical at all. A supermarket etc. can not reprice items in their inventory every few days. It needs to be a fixed price for the supermarket and then some extra activation step where the actual conversion at current market price happens. Giftcoins.me got that part right and it is a very interesting project.

You mean dangerous for the users? I am not sure I would call it "dangerous", but yes, the risk of slippage is assumed by the user. That's why the 1.5 % round trip fee is typical, not guaranteed. If you happen to use it in the middle of a crash you will probably end up paying more. That's why Bridgewalker always gives you an estimation on how high the currency conversion overhead is.

So as one of screenshots show, if I enter 5 USD, I see something like this: "Recipient will receive 0.10991995 BTC (~ 5.00 USD). From your account 5.03004 USD will be deducted. This is a difference of about 0.6 %". So in this case you paying 0.6 % more than the recipient will receive. And market spread is already taken into account here, because for the recipient a market order sell is assumed (albeit without any exchange fess the recipient might pay) and for you a market order buy for acquiring the bitcoins plus exchange fees is assumed. If there happens to be a much larger gap, you will see this percentage value going up and might want to wait for the markets to settle before doing your transaction. But in my testing over the last months this hasn't really been a problem for me.


Only Bitcoin.

Not sure I follow, can you clarify what you mean exactly? The 1.5 % are in and out, so that already includes using it for something, like let's say shopping at bitcoinstore.com . Or are you talking about turning Bridgewalker-USD into actual bills in your hand? Then yes, that will probably require an extra cash out step somewhere with additional fees. And that's a good point - I personally would consider this an interesting benchmark: Person starts with a $20 bill, turns that into Bitcoin, and a couple of weeks later pays some merchant and the merchant has X amount of USD in his pocket at the end. What is the fee for that complete cycle? If the user keeps bitcoins for the couple of weeks there is pretty much no telling what he ends up with - the market might have moved in his favor or against him. With Bridgewalker that uncertainty is taken out of the equation, for an additional 1.5 %. With fees for acquiring bitcoins and then fees the merchant is paying to convert it back, we probably can not beat credit cards at this point. But I would like to think that we can at some point, if we continue to optimize at all of these points.


I might release the Android client as open source at some point, but the server will probably stay closed source for the foreseeable future.


My thinking exactly! :-) And regarding that: Transfers between Bridgewalker users are instantaneous and free.


It's mostly a question of liquidity. If market spread is very large all of the time, you end up not getting the best price when moving in and out of Bitcoin which can increase that "round trip fee" quite a bit. That's why I started out with Mt.Gox USD market which is quite liquid. I would like to offer a Euro version in the near future.


At the moment your Bridgewalker account will always be denominated in USD, you can not change that. But in theory there could be a separate Euro version of Bridgewalker (and hopefully will be at some point) and then you could definitely exchange money between the two. It would use Bitcoin as the middle man: Bridgewalker-USD -> BTC -> Bridgewalker-EUR.


The Bridgewalker server is currently hosted in Germany.

Glad you like it! :-) .. I agree with some of the points you make! Although personally I would rather see something like Bridgewalker becoming obsolete in the long run and - as the Bitcoin economy matures - things moving completely over into BTC. If only for efficiency reasons (avoid constant currency exchange). But at the moment that's simply not practical and probably will not be for quite some time. The popularity of payment processors like BitPay show, that at this point it is necessary to peg prices to USD because there is just too much volatility. And that's fine. This tool aims to bring the same concept to the customer side. Where merchants accept BTC and end up with USD, customers can use Bridgewalker to hold USD and pay in the form of Bitcoin transactions. The important point is, that Bitcoin is the neutral interface between them.


Scanning the QR code works! I support both things like "bitcoin:1asdf?amount=0.123" as well as the "broken" variant with "bitcoin://1asdf"

The URI link does not work at the moment, I haven't looked into where exactly I need to hook into there. But I definitely plan to support that! I'll let you know, when an update is available.


Aw, yes, I should put more details about that on the site. The account is with Bridgewalker and all Bitcoin transactions are going to and from Bridgewalker's Bitcoin daemon. Bridgewalker in turn has then one single account with Mt.Gox and transfers bitcoins between it's own wallet and the account at Mt.Gox to do the trading. The end result is, that most user funds end up in Bridgewalker's Mt.Gox account in the form of USD. So you need to trust that a) Mt.Gox keeps their user accounts safe in general and b) I keep the access to Bridgewalker's Mt.Gox account in particular safe. Only a small amount of funds are in BTC at any time, basically just a small hot wallet to be able to send out transactions quickly.

I'll answer more questions later, as I will be away from the computer for a few hours. Thanks for all the feedback so far!

The "interface" to the rest of the world, so to speak, is only Bitcoin. Bitcoin in, Bitcoin out. So in order to fund the account, you will have to buy bitcoins from somewhere else and transfer them. That might seem like an unnecessary step (use USD to buy BTC, just to have Bridgewalker convert it back), but I cannot and do not want to accept USD. Others are much better at selling coins and Bitcoin is the universal glue between us.


Thanks! I absolutely agree. This is certainly not for everyone and I am all for doing everything directly in BTC. But this is a middle ground for people who are not quite ready to trust some weird internet money, but see the appeal in the Bitcoin payment mechanism as a kind of "cash for the digital world".