Secure boot from Nitrokey storage?

Question

I was looking into buying a NitroKey. To my surprise I found the following statement in the brochure:

Keep a Secure Operating System With you at all  Times

Securely boot Windows or Linux directly from Nitrokey Storage. Nitrokey Storage encrypts and protects the system against manipulation, such as the installation of surveillance software via „Evil Maid“.

I am familiar with keeping a bootloader, kernel and initramfs with encryption keys on a USB stick to prevent tampering. But such a storage by itself is unencrypted, otherwise the bootloader + kernel cannot be loaded by the system.

But in this case I'm a bit confused how it works. Most sources I found regarding its encryption mechanism, is that an application on the host should ask you the device PIN to decrypt files on the storage. So unless it ships with some internal boot-loader logic, how is it bringing up a system in a state to can ask the PIN? Is the NitroKey really boot a system in a revolutionary new way?

I've tried looking for secondary sources to this claim, but no avail:

• Nitrokey FAQ, does not say anything related to booting
• Firmware update guide tells to --suppress-bootloader-mem, which gives me the sensation there is a bootloader. (Google found me this link based on the word boot probably)
• Installation guide, nothing there.
• A forum thread from people who imagine that booting from a stick means running a complete OS from it, instead of offloading the OS to encrypted hard drive. No clear answer there either.
• More mentions about a bootloader, but not what it does.

Answer 1

Although not exactly what you may be looking for (and a year later, so you may have found a way or given up on the idea), the fact that you can setup the unencrypted partition on a nitrockey storage to be readonly (hardware backed) is enough to me regarding "a secure boot process".

Although still not encrypted, as long as you don't provide the Nitrokey's admin password (not even the "User" one), it'll stay readonly, hope that'll be tamper-proof enough for you (there shouldn't be any sensitive data in these elements anyway, so being encrypted should not be the goal in itself).

Answer 2

Just going on the brochure, it seems that this is almost over reach - I expect that the same functionality which provides plausible deniability leaves part of the disk unencrypted and able to boot without requiring keys as per a normal USB key. (I expect there is additional functionality providing a secure enclave, and the underlying disk may also be encrypted in a way transparent to the USb interface, but that's irrelevant to this particular claim)

The key is that they specified an "evil maid" attack - which means someone compromising the system with physical access when you are absent. Because you can always take your key with you, you can ensure the OS boots cleanly bypassing any malware added to a boot loader on the unattended PC.