Wednesday, November 21, 2012

SMS Service dysfunctioning in Italy

Some operators in Italy don't seem to transmit SMS messages properly to twilio. Please don't rely on the SMS transaction service if you are doing trading in Italy.

We are trying to resolve the problem as soon as possible.

Tuesday, November 20, 2012

Start Your Own Money Press

Physical cash is old and well-working concept. It has a good privacy model, it is relatively anonymous and it is easy and fast to use. Physical cash won't go away anytime soon, because it works so well.

However there are some problems, which might become bigger issues in the future. Central banks are always able to print physical money as much as they want, which will cause devaluation of physical cash for everyone. Additionally, even if you believe in central banks, private entities with skills and resources are able to print cash as well. In fact, there already exists counterfeit cash which even skilled experts can't distinguish from goverment-printed money.

Bitcoin solves effectively the counterfeiting problem, or so called double-spending problem. It also removes nicely the need to trust the central bankers. However, being a virtual currency, using bitcoins is often seen much more difficult than using cash or other traditional payment methods.

One nice concept around Bitcoin is a paper wallet. It allows anyone to store bitcoins on a paper, like physical cash. Unlike physical cash, bitcoin paper wallets aren't suitable for large-scale trade, but they have other useful applications:

  • Getting people introduced to bitcoins, a learning tool
  • Relatively secure way to store bitcoins - generate the paper wallets offline on a computer, print them out, and store them in a bank safe
  • Trade in high-trust environment, such as between friends and family
simplest possible bitcoin bank note
The simplest possible bitcoin bank note contains only the private key. You can derive the corresponding Bitcoin address from the private key. However usually it makes sense to include also the corresponding bitcoin address, to make usability easier.

Other than that, only the sky is the limit. Bitcoin paper wallets come in all sizes and forms, and it is also fairly easy to create your own design. You can store any amount of bitcoins on paper wallet - be it one million bitcoins or 0.00000001 bitcoins (one satoshi). You can also load them as you go - it might be useful to have receiving addresses in your wallet, just in case. You can store the private key somewhere else securely.

The best thing about bitcoin paper wallets is that they are not dependant on any of the running bitcoin services, except the bitcoin network itself. Even if invidual web sites come and go, the Bitcoin network highly probably will stay up and running, and you will be able to redeem your bitcoins even aften waiting 10 years.

Printing your own Bitcoin bank notes provides easy way to print your own bitcoin cash. The steps are:

  1. Start your web browser. Use incognito window or similar.
  2. Go to
  3. Disconnect your computer from the internet
  4. "Paper Wallet" -> "Print"
  5. Clear browser cache and all private data, restart browser
Tinfoil hats will not be happy with these instructions, therefore I have included extra security cautions in the footnote [1].

After printing, you can apply some kind of tamper-evident sticker on top of the private key. Also one option is to laminate the wallets, as I did - it makes them more durable.

Creating your own custom design is just a static html/javascript page, you can download it to your computer and modify the behaviour to match your requirements. The most obvious thing is to create your own design for the bank note.

This can be done with following steps:

  1. Create your custom artwork with any program such as inkscape or photoshop
  2. Export it to png at 795x430 pixels
  3. Convert the png file to base 64 data
  4. Replace the contents of the img tag, id "papersvg" inside javascript 

You can also replace the site logo (id logo), or localize the site to your own language. Then you can upload the html file to your own server, so anyone can use your design to generate bitcoin paper wallets.

Loading and redeeming paper wallets

Naturally any QR-scanning capable bitcoin wallet app can be used to load the paper wallet. Not all apps can be used to redeem the contents. Our web wallet can be used to sweep the transactions from the private key. It works on iPhone and Android, also with one-tap if configured properly. doesn't import the private keys, it just sweeps the unspent transactions to the wallet address and after that forgets the private key.

Additional resources and links - beautiful multi-coloured banknotes - my own take, really minimalistic and small bitcoin bank notes and storage sheets - really nice bitcoin paper wallet design as a PSD and SVG file - other design by casascius - lots of designs and discussion - on github

[1] Extra security cautions for using

  • Use linux from USB stick, such as tails (handy amnesiac distro)
  • Don't connect the printer to a internet connected machine - ever (printer manufacturers are controlled by reptilians)
  • Download the file locally and validate the SHA1 checksum provided by the author
  • Wrap everything in tinfoil

Thursday, November 15, 2012

Accept Bitcoins On The Restaurant Day

The International Restaurant Day is coming again on next saturday, and hundreds of small restaurants will be popping around the world. The event started from Helsinki, Finland, and has been spreading since then to new countries and cities.

For small-time restaurants, payments are always a problem. Cash is cumbersome, and it is hard to keep enough change for your customers. Accepting credit or debit cards is really expensive, and if you want to set up a temporary restaurant you usually don't want to invest in a credit card terminal.

Bitcoin is nice, because in addition to solving the central banking problem, it also fixes the change money problem, and also it is very easy to accept bitcoin payments. Below I will visit different ways to accept bitcoin payments from your customers. - probably quickest and easiest 

All platforms: iPhone, Android, laptops, any device with a web browser

To set up accepting payments, just go to and the service will generate a random web address for you, which is the key to your bitcoins. Bookmark it, and you can start accepting bitcoins. The service supports currency conversions with 24h exchange rate, so you don't need to worry about the exchange rate, and the rate will be fair to both buyer and seller.

From your settings, turn off "Use Static Address". This way the service will generate new address each time you receive payments, allowing you to separate your customers more effectively.

To move your bitcoins elsewhere, you can use QR code scanner on iPhone and Android. You can also send the URL to your email, and handle cashing out from your computer.

Electrum +

Safe (only receiving), any device with browser, including iPhone, Android and Kindle!

This merchant solution is basic, but it works. Note that this is not a wallet software - it is only for receiving money. You have to pair the web site with an electrum installation.

Android standalone wallets

These are standalone, which means that they store private keys on your device.

BitcoinSpinner - really fast and easy, no block chain download.

Bitcoin Wallet (Schildbach) - oldest and stable. There is block chain download, therefore I can't recommend it to newbies.

Others - browser-based, or standalone for Android and jailbroken iPhone. Haven't used it myself, but generally recommended lots in the community.

Electrum - my favourite desktop client. Friendly and instant.

Giving change as bitcoins

You have run out of pocket change and can't give your customer money? Maybe he/she will accept bitcoins. Print some paper wallets from When customer requests change, zap change amount worth of bitcoins to a paper, and give the paper to the customer. The customer can cash out his/her bitcoins from his computer at home.

Cashing out bitcoins to euros/dollars/fiat

There are lots of exchanges which allow you to convert your bitcoins to more traditional currencies. My favourite bank transfer-based exchange is

However, if you want to spur up the local bitcoin economy, look for a cash dealer at - you can also set up your own "selling bitcoins" advertisement, and help local people to get to know bitcoins a little better.

Hope everyone has a great Restaurant Day! If you consider accepting bitcoins and have any questions, send me an email to . Feel free to ask anything. Also if you will accept bitcoins on next saturday, give me a note - I can advertise your pop-up restaurant for free :)

Tuesday, November 6, 2012 profit calculator

Want to calculate how much money you would be able to make by being a local trader? One of our users, Julian, has created this great calculator, which can help you estimate it. Thanks Julian!

Link to the spreadsheet