Securely create Nostr private keys with a Coldcard hardware wallet
If you are building your Nostr identity (?), you want to be sure that it won’t be hacked or stolen. It would lead to loss of al your followers and your reputation, you would have to start all over again. To avoid this scenario, secure handling of your Nostr private keys (?) is extremely important.
Coldcard is one of the most respected Bitcoin hardware wallets, a device that is being trusted by thousands of hardcore Bitcoiners to handle their private keys securely. Both the Coldcard MK4 and the Q1 are amazing devices, full of advanced security features.
Beside Bitcoin private keys, the Coldcard device can also derive Nostr private keys securely offline. On this page we will describe how the Coldcard can be used for Nostr.
Note: As of now the Coldcard can only be used to securely create private keys, not (yet) to sign for Nostr messages.
What is a Coldcard hardware wallet?
Coldcard is an advanced Bitcoin hardware wallet that can be used for air-gapped signing of Bitcoin transactions. The security features include among others a pin that bricks the device, words to check whether the device is tampered with and a function to create a private key by rolling a dice. BIP-85 (?) enables you to derive child seeds from the master seed, this is how the Nostr keys can be created. There are two models available: The Coldcard MK4 and the Coldcard Q1.
Coldcard Q1
The Q1 is the newer and more user-friendly version. The firmware is mostly the same as the MK4, but the architecture of the device is very different. The Q1 is complete with a bigger screen and a keypad.
In addition to signing with a Micro SD card, optimal air-gapped signing with QR codes can be done on this device. This is both more user-friendly and more secure.
Coldcard MK4
The MK4 is the fourth in the production line of the original Coldcard series. The device is famously called a calculator, because that is how it looks like.
The device is transparent, so you can see all the elements in the hardware device. Air-gapped signing happens through a Micro SD card, which is used to transfer signing information between the hardware wallet and the online device.
The Nostr functionalities of Coldcard
Nostr keys can be created by using BIP-85, a Bitcoin Improvement Proposal that enables the generation of child keys from a master key. It can be done by choosing Advanced / Tools > Derive Seed B85 > 32-bytes hex. This child key can be imported in a browser extension like Alby (?) or directly into a client (?).
Securely signing is not yet possible, but it is expected that it will be in the future. When ‘key delegation’ gets implemented, delegated keys can be brought into the online world to simply be cancelled if they get compromised. Or maybe Coldcard finds another way to do it, we will keep you updated!
Conclusion:
Coldcard is one of the better Bitcoin hardware wallets. The device can be used to securely create Nostr private keys too. Secure signing for Nostr messages is not yet possible, but we expect this to come in the future. As for now it is still useful in combination with a browser extension like Alby, especially if you are a Bitcoin holder too.