This guide will show you how to make a cheap and useable physical Bitcoin, perfect for use as secure cold storage. It utilizes multiple technologies to allow you to both top-up funds and restore your private keys.

These technologies include:

- QR Code. The public key on the outside allows you to use a camera to scan the code and retrieve your bitcoin address.

- NFC Chip containing your coins public key (aka your bitcoin address) and the Bitcoin URI. Once scanned with a phone or tablet, it automatically launches whatever bitcoin app you have installed and inputs the address, allowing you to top up funds without physically opening the coin.

- Pen and paper. You can physically write out your private keys and place them inside the coin. It’s simple, but effective, just make sure you triple check it!

- Micro SD card. This contains a backup of your public and private key + anything else you might like to store. The advantage of having this is that you can also include detailed instructions and install files for various bitcoin wallets, so you’re able to re-import your keys on any platform and gain access to your funds. You could even partition the drive and install a live boot operating system like Tails, which now comes with its own bitcoin wallet as standard.

The coins are very cheap and easy to make, and are portable and robust enough to store in a variety of circumstances. The cases are called ‘coin capsules’ and are used by coin collectors to keep their money safe. Ironically, this is not much different from what we aim to do. They are made of acrylic plastic, so you could also use special plastic glue to 'weld’ both halves together, resulting in a fully sealed coin. The only way to recover the private keys would be to break it open.

PHOTOS

- Front
- Back
- Thickness
- Multiple Coins
- Inside

PARTS/MATERIALS

- Coin capsules (Multiple shapes and sizes are available. Square and rectangular ones will be easier to cut/assemble by hand.)
- Micro SD card
- NFC chip (Needs to fit inside your case and also have enough space to store your bitcoin address)
- Foam sheeting
- Paper/Card for QR Codes

TOOLS

- Phone/Tablet/Computer with NFC capabilities
- Craft knife or scissors
- Printer
- Computer (to generate QR codes + write contents of Micro SD)

HOW-TO GUIDE

Step 1. The first thing we need to do is generate a wallet and the private keys for it. You could use a generator like [https://bitcoinpaperwallet.com] or if you want to use an existing wallet, following your wallets guide to generate private keys. Ideally, this should be done on an airgapped computer (aka one without internet access), to reduce the chances of anyone stealing your funds.

Step 2. If you haven’t generated one already, use a QR code generator (preferably offline) to generate the QR codes for your public and private keys. For the public key you can add the bitcoin URI prefix to your address [https://en.bitcoin.it/wiki/BIP_0021] so when it’s scanned it will automatically launch whichever bitcoin apps you have installed. Obviously be careful not to inadvertently reveal your private key QR code to any person or computer you don’t trust.

Step 3. The next step is to print out your front cover and QR codes. This will be different depending on what image editing software and case size/shape you have. You can pick up the Bitcoin logo vector graphic here [http://www.brandsoftheworld.com/logo/bitcoin]. Again, this might be paranoid, but be careful on what printer you print these codes on too, since it may be compromised (especially if it’s connected to the internet). A sophisticated attacker could retrieve the QR code data from the memory of the printer too so bare that in mind. If this is too much hassle, you could probably skip the private key QR code and only include your private key on the micro SD card instead.

Step 4. Use your craft knife or scissors to cut out your new coin cover and QR codes. If you have a choice, pick square coin capsules because it makes this step way easier.

Step 5. Get your foam sheet and cut out the insert that will include your micro SD card.

Step 6. Take your micro SD card, put it on the foam insert and trace around it. Now use your craft knife to cut out the shape. Your micro SD card should fit snugly inside.

Step 7. Load up the contents of your micro SD card. Like I mentioned above, you could include different information such as your public and private keys (perhaps encrypted), detailed instructions on how to restore them, as well as multi-platform install files for various bitcoin wallets, so no matter how far in the future you decide to resurrect your funds, you will be able to.

Step 8. Using a phone, tablet or stand alone NFC reader/writer, write your public address + bitcoin URI to the NFC chip. There are a million different apps and tutorials out there, so find one specific to the tech you have. Test it to see if it has worked correctly. If you have an option to lock the chip and make it read-only, do it.

Step 9. Stuff the multiple inserts into your coin and seal it shut. Remember to put the public key QR code on the outside. If you have acrylic glue you can now physically seal it so it’s air tight.

You now have a fairly secure physical Bitcoin that can easily be topped up and stored for decades.

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BY CHRIS ROBINSON