The effort started as an educational project for Conor Patrick, a hardware engineer, who wanted to see if he could build an affordable security key from scratch. Thank you in advance for your suggestions.A small team of engineers is building a line of hardware security key that is completely open source and supports the new FIDO2 standard and can be used with mobile phones to provide strong two-factor authentication. But unless I missed something, it doesn't support NFC that makes it hard to use on Android because the main onlykey is not USB-C. KeePassXC only lists onlykey as alternative to yubikey. While this is fine on the PC, it doesn't seem like an every-day option on Android. I only glanced at it, seems like you use the nitrokey and gpg to encrypt your keepass database then, nitrokey will be required to unlock the encrypted database (certs saved onto the nitrokey itself) before you can further unlock it with keepassxc via password/keyfile. There is a tutoral on how to use keepassxc with it, but it is very specific. The nitrokey cannot be configured in this matter.

So I can set this phrase on my every-day yubikey as well as on another that I store in a safe location in case I lose the main yubikey (wouldn't want my database to be locked forever if that happened).

The yubikey software allows to change the passphrase (or rather, the HMAC-SHA1 Challenge Response) used for this hardware key authentication per device. What do I mean by can be used natively to unlock keepassxc? Well, the yubikey can be configured to act as hardware key this means, when I want to unlock my keepassxc database, I need the physical key to be inserted to unlock my database - besides my password and keyfile. Optional: key can also act as storage (ideally even with an option for unencrypted storage so one could store keyfiles and data that would be accessible without the need for vendor-specific software) Open source (optional, but highly preferred!) However, I would like to replace them with another solution, if there is one that meets my requirements:

Open source yubikey alternative