As of 2023 June, the `hopenpgp-tools` is not part of the latest Debian 12 stable package repositories.
To install it, go to [https://packages.debian.org/sid/hopenpgp-tools](https://packages.debian.org/sid/hopenpgp-tools) to select your architecture and then an ftp server.
Edit `/etc/apt/sources.list` and add the ftp server:
```
deb http://ftp.debian.org/debian sid main
```
and then add this to `/etc/apt/preferences` (or a fragment, e.g. `/etc/apt/preferences.d/00-sid`) so that APT still prioritizes packages from the stable repository over sid.
```
Package: *
Pin: release n=sid
Pin-Priority: 10
```
**Note** Live Ubuntu images [may require modification](https://github.com/drduh/YubiKey-Guide/issues/116) to `/etc/apt/sources.list` and may need additional packages: