You mention that SmartCard-HSM/Nitrokey HSM are open source, which to me seems a bit disingenuous, since the most important part, the applet itself, is closed s

You mention that SmartCard-HSM/Nitrokey HSM are open source, which to me seems a bit disingenuous, since the most important part, the applet itself, is closed source AFAIK. You can't get the source that you can compile to a .cap file and upload it to your own blank java card. I'm using this instead https://github.com/philipWendland/IsoApplet https://github.com/philipWendland/IsoApplet