HW1 tiny BitCoin hardware wallet

While the trezor is certainly a great device for securing BitCoins, I’m also interested in alternative hardware wallets. Even in my very first discussions about increasing the scurity of BitCoin we talked about SmartCard solutions. After all, that’s also how I secure my GPG keys. But a regular SmartCard alone only protects the keys. If the computer is malware infected, it could sign another transaction than the one you initiated, and thus spend all your coins at once. The trezor solves this problem nicely with displaying the transaction details on the screen, waiting for a button press to confirm. Then came the HW1, a tiny BitCoin hardware wallet, based on smartcard technology with some extras. Since it has no display nor buttons, I was ready to get somewhat reduced security compared to the trezor. But in fact they are also very clever, and it turns out the security is just as high at the cost of a bit of convenience. But as I understand it, that level is configurable. I just opted for the more secure option.

So, If I want to spend some Coins from my HW1, I plug the dongle which is smaller than a regular key on my keychain into an USB port on my computer. Then I start up electrum, and send the coins. Now the HW1 has to sign the transaction. It asks me to remove the dongle and plug it into another computer, that is preferably not connected to the internet. If I don’t have too much funds on this wallet, I can also plug it into the same one again. A text editor should be opened beforehand, and it should have focus. The dongle then acts as a keyboard, typing the transaction details along with a TAN code to validate the transaction. Next I remove the HW1 again, and plug it into the former computer. I type the TAN code, HW1 signs the transaction, and electrum distributes it to the BitCoin network. That’s it: simple and secure.

Just as electrum itself and trezor, the HW1 uses a deterministic hierarchical wallet. To be sure I can trust the device and the method in general, it was not enough for me to test that I can spend from it. I wanted to also be sure I keep my coins in case the device gets damaged or lost. That means I have to be able to restore it from a seed. The seed is generated when I first initialize the dongle. And like the TAN code it is printed out in HID keyboard mode. If you have it print it on a machine that could be compromised, there would be no point in using a hardware walled in the first place. So have it print the seed to an air-gapped secure computer. If you already initialized your HW1, you can’t restore another seed onto it, unless you reset it first. I couldn’t find any documentation on how to reset it though. A developer told me to enter a wrong PIN three times to reset it. After that, don’t choose restore, but initialize. In the BTChip personalization manager that follows, you choose restore. I did this on a machine where I removed the harddisk, and booted from a fresh USB stick. Getting electrum usable with all the required plugins and libraries was the most work. Before typing in the seed, unplug the network cable and disable WiFi. After the seed was typed in, and the dongle restored, I issued “sudo dd if=/dev/random of=/dev/sda” and waited for the kernel to go belly up. That’s for making sure no sensitive information remained on the USB dongle. Don’t do this on your regular computer.

In conclusion, I can say that:

  1. The security is just as high as with the trezor, if you let it type the TAN on a computer that is temporarily offline. But the convenience obviously suffers.
  2. If you only use it to store medium value funds, you can have it type on the same device, at reduced security. In that setting the convenience is about the same as with the trezor.
  3. Where the biggest difference lies for me, is restoring the device from a seed. Preparing a fully equipped air-gapped computer to securely restore the dongle from a seed proved to be quite some work. While with the trezor, you don’t need an additional computer. Luckily that’s a task that is required infrequently.

While the experience with the trezor was smooth from the beginning, I tested a lot with the HW1 to gain confidence with it. I found some minor bugs. I had the computer freeze a couple of times. I saw lots of messages about dongles not found. I had to reconnect and start over many many times. Some things were not documented or not obvious. All these problems became lesser the more I tested it. I can only explain it that way that I grew a sense for the correct timings and steps required. In the meantime I use it without problems, but I have the feeling that it is not as robust as the trezor. It will work in the end, but you might have to try a few times before it does.

I packaged the python library that is needed for the plugin for ubuntu. Once all parts and dependend libraries are out of beta, I will also try to get it into debian. On ubuntu, you can install it like this:

sudo apt-add-repository ppa:richi-paraeasy/bitcoin
sudo apt-get update
sudo apt-get install python-btchip

Ah yes, and there’s the price difference. A trezor costs $119 while a HW1 is just $20. At the moment they have a 2 for 1 offer, so go hurry.

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