Review 38 – Opendime


For a long time I’ve watched people create physical Bitcoin, which has always baffled me. Don’t get me wrong, they look really freaking cool. We all know what Casacius coins look like because they’re on every mainstream news story about Bitcoin. Newer ones like Titan, Denarium, or the series from Infinitum are also really sexy. Even the cheap ones like the Satori Coin, sold out of vending machines in Japan, are kind of cool looking. However, attaching an amount of bitcoin to them comes with a whole host of security issues. This goes for any coin, note, or paper wallet, whether made of paper, plastic, or steel. To be succinct: either a central authority must ensure and protect the bitcoin to be issued on demand or you must trust that the issuer or last person to handle it didn’t keep a copy of the private key on the physical coin with which to steal your funds. But that has been resolved. One company has made it possible to convert bitcoin to physical form without limits. Today we’re going to look at Opendime.

opendime_1Opendime is a small, cheap, USB stick that allows you to deposit any volume of bitcoin to be spent or transferred like bank notes. You can easily check the balance of the Opendime by plugging it into a USB port and opening a file. They can be passed on from person to person multiple times. And when someone wants to spend the bitcoin deposited in them they simply break the seal and sweep the funds.

opendime_2I pre-ordered a pack of 3 Opendime sticks and, after a short wait for production, they arrived in the post from Canada in short order. They even threw in a Coinkite sticker, the company that produced Opendime.

opendime_3The Opendime stick itself is a nearly bare board, read-only, USB flash drive.


opendime_4Upon plugging in the Opendime you will see that it gets listed as a drive.


opendime_5The drive has a couple files and a couple folders.


opendime_6The README.txt file is handy for explaining the basics.


The random number generator on the drive needs entropy to ensure randomness when creating the private key associated with the Opendime. To do this, we need to drop files onto the drive.


opendime_7I dropped 3 files onto the drive. One was a bundle of data delivered to me from The other two were pictures I thought were symbolic. One was bitcoin related. The other was an image I’ve always loved from probably my favorite horrible movie.


The BIN file and pictures don’t really matter except that they introduce entropy. It’d be best if you used files to which only you would have access, like pictures you’ve taken, your poetry, etc. They aren’t saved on the drive. They aren’t sent anywhere. They’re just used for this process and then forcibly removed from the drive.

opendime_8Once I had loaded enough data the drive ejected and remounted itself. The first thing I noticed is that the light flashing pattern changed. Another change, as you can see, is that the data on the drive changed. The address.txt file has the Bitcoin address now associated with my Opendime in text form. It’s also in QR form in the qrcode.jpg file. I did verify that they matched.

opendime_9The README.txt file is now different as well, and full of instructions on where to go from here.

opendime_10To address the elephant in the room: yes, there is a file called private-key.txt. If you open it up it says “SEALED” and refers you to the README.txt file. There’s nothing of consequence in it… yet.

opendime_11For a test, I decided to send 0.01 BTC to the address created by my Opendime. I opened the QR code and used it, but you could also copy/paste the address.

opendime_12And it worked. This Opendime is now worth 0.01 BTC. No matter the market, no matter who owns it, this Opendime is always worth a bitcent. If someone were to say to me that they wanted 0.01 BTC for an item or a service I could pass this Opendime to them.

opendime_13They could verify the Bitcoin address associated with it, and they could know without a doubt that they hold 0.01 BTC.

You see, the Opendime is a bearer instrument. Much like cash or bearer bonds, the Opendime isn’t assigned to an owner, it can be transferred from person to person, and ownership is the only burden of proof required. It’s very much a physical embodiment of the old addage, “If you aren’t the sole holder of the private keys you don’t own the bitcoin.” If you hold the Opendime in your hand you know you own the bitcoin because the only way to get to the private key is to destroy it.

opendime_14You see, in order to unseal the private key locked inside the device you have to snap the bit out of the middle. This is pretty tough, so you may want to use a pocket knife, a key, or perhaps a coin to get some leverage.

opendime_15Once that piece is removed and you plug it back in the lights will change and you’ll see that the data has changed yet again. Specifically, the private-key.txt file is no longer sealed.

And then you just have to sweep the funds. You can do this with several wallets I’ve mentioned in my articles, like Electrum, Mycelium, or Copay.


The funds were safely removed.

So, what makes Opendime different from other physical bitcoins?

Zero trust. The drive is nearly completely read-only, except when seeding it. The entropy is seeded by you using files only you would own. The private key is sealed until the drive is physically broken. The drive, once broken, is changed forever. So even repair attempts won’t work because the drive behaves differently after it’s broken.

Cheap and disposable. Seriously, at $12.50 each and they come in packs of up to 12, they’re not exactly breaking the bank here. Granted, I wouldn’t use them like Credsticks in Shadowrun, but you could.

No set denomination. This means that you could increase the value of these things at will just by adding more funds. When they become worth it you could break them open and sweep them clean.

Opendime doesn’t necessarily recommend them for cold/long-term storage, but they do say that you could. The drive itself will hold the data nearly indefinitely. You could always set one up, copy the address and QR code, and then lock the drive itself up in a safe or deposit box. You could use the address or QR code to load it with funds on a regular basis, storing the drive securely for future use. At some point in the future you could then retrieve the drive and sweep it.

Other uses? Opendime recommends gifting them preloaded or maybe selling them. I rather like the idea of replacing paper wallets with them. It has always subconsciously bothered me that a digital money was arguably most secure when printed.

As for using these things like banknotes, transferring them between people like cash, using them to pay for goods and services? I can’t really get on board there. Sure, you could do that, but they’re missing a few features. I can’t tell how much is on them without plugging them in. If I can plug them in I can run a Bitcoin wallet. If I can run a Bitcoin wallet I can just transfer funds. Without a display they’re no better than just transferring bitcoin.

After using the Opendime for a short period of time I can already see a niche or two in which this device can fit in my usage of Bitcoin. I really do recommend grabbing a few. I plan on keeping one as a collectible at the very least, but I will probably pick up a few more just in case. If you’re interested, just go to to order your own.

Posted in Gadgets, Other, Reviews

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  1. […] it possible to convert bitcoin to physical form without limits. I did a review of a device made by Opendime which is a small, cheap, USB stick that allows you to deposit any volume of bitcoin to be spent or […]

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