Get Yours!

Visit Opendime.com to get more Opendimes!

Aliexpress has the M5Stack systems... many options and packages. At a minimum, you'll need the "Basic" plus a "USB", but other combinations are possible.

Install

• install serial port drivers for CP2104 chip from Silicon Labs

  • https://www.silabs.com/products/development-tools/software/usb-to-uart-bridge-vcp-drivers
  • must enable "system extension" immediately after install
  • expect to find /dev/tty.SLAB_USBtoUART when M5Stack is connected

• download and install Ardinuo

• for MacOS, follow this guide

• install an additional libraries: Tools > Manage Libraries...

  • "USB Host Shield Library 2.0" .. search for "usb max"

• open "verifier.ino" and press Run

• you need the USB unit in your stack, of course.

How it Works.

Every Opendime comes with an x.509 ceriticate that is signed by the factory. The public key which that certificate atests-to, is stored inside an ATECC508A chip (in fact, it has never left that chip, and was generated inside it). The x.509 certiciate chain is verified all the way to the factory root certificate, and then the public key from the certificate is verified against a (nonce) message signed by the Opendime. The process does take a few moments.

Code can be found in certs.ino, and is equivilent to the python code shipped on every Opendime, in the file trustme.py.

TODO

• initialize factory-fresh Opendimes with good entropy so they will pick a key
• cycle through a few good third-party websites for balance checking QR
  • middle click for next site
  • remember your favourite
• improve bitcoin signed-message verification process
• display current balance on screen with help of Internet connection

Important

Only use your own verifier to check an Opendime! The M5Stack platform is open to any changes, and it would not be hard to modify the code here to display something fraudulent.

You can only trust your own verifier and ideally build it yourself from this source code.

Comment on Balance Display

It would be great to show the current balance on screen. It's not too hard, but requires Wifi access and a backend service of some kind. That could be an Electrum server, or a Bitcoin web service. Wifi access requires a setup process so the M5Stack can get a wifi password to use, and the interaction with a back-end service may reveal your location and/or identity plus it may tie you into future and pass applications of the specific Opendime.