I like how the Passport can't be connected to anything, because people have made spying devices shaped in a USB port and that makes me feel slightly paranoid because however unrealistic it may be (emphasis on unrealistic) I still worry that USB hardware wallets like Ledger might be modified by someone to steal coins.
This 20 year old mobile (a.k.a. "new" hardware wallet) also has interfaces to exploit vulnerabilities: The SD slot and the camera (yes, parsing data from a QR code can create vulnerabilities).
It's not like it is
unhackable.
I'm guessing the microSD card can be taken out and replaced, although I don't see a practical reason for doing that unless the entire hardware wallet state is stored on it. It could also be that the whole wallet OS is stored on it too, no details about that were given by the website however. They say the hardware is open but what really defines open hardware? An open hardware device sounds like skilled people will be able to reverse engineer the software running it, for the software must also be open for some open hardware to run on it, because by reason software that is proprietary and closed to the vendors making the hardware wallet can't be ran on open hardware.
All that sounds needlessly abstract and there has to be a standard to measure open hardware by. At least to me, someone showcasing open hardware feels like end users can build their own device with similar components from scratch, or at least having the ability to replace every single part inside (like software). No obscure screws or gluing that is not available in retail markets.
What I'm trying to say is, I don't think open hardware is inherently safer than conventional hardware, if someone can figure out all the signals sent to pins that make the device do different internal functions. Specifically, someone could build an SD card that sends a different encrypted private key belonging to a hacker when a read for that private key file is queued by the OS, and that's doable since the SD card ultimately handles reading and writing data.
It wouldn't be able to silently replace the private key file at write time with its own (stealing private keys) because the encryption happens in the memory module not in the SD card, so some attack vectors are thwarted but only as long as you can't control the piece of hardware that's responsible for the operation you want to tamper with. Now if someone also replaced the memory in open hardware with a malicious one that retains the private keys unencrypted when the device is trying to encrypt them to save to disk, then stealing the private key becomes possible, just take out the SD card and connect it somewhere else to copy the private key.
And that's just one of several attack vectors that open up by controlling a second component. So eventually, again assuming "open hardware" means people can build a lookalike or replace parts inside, the more components you can replace, the more parts of the device you control which means more security holes pop up, and thinking about security holes in the sense of real holes in a wall, if you keep drilling holes in the wall the whole wall will be gone, and if you have control of replacing over all hardware parts, the entire security system collapses.
Same thing applies to the camera, or any other hardware part for that matter, if someone can replace the camera with one that's programmed to change all QR codes into a set of predefined QR codes corresponding to hacker addresses and transactions.
Without going off topic I'll also mention that both an open CPU architecture, ARM cortex, and closed ones, Intel and AMD, were all vulnerable to a hardware flaw called Spectre that controls hardware how I described it above. And nobody even had to replace hardware parts for the flaw to get in, it was accidentally included in the hardware design. So both "open hardware" and closed hardware are both vulnerable to design errors.
The Passport doesn't feel like open hardware at all, because all we can see right now are a list of parts inside and some specifications. Every device has those.
