Seeking a USB switch – a device that toggles USB input(s) between two or more outputs
Use case: I have a two computers. Id like to toggle peripherals (keyboard, mouse, etc) between these machines at the press of a single button
Issue: blindly buying a USB black box and plugging it into my machine could expose me to malware. But without tearing random models apart & performing a forensic analysis, I have no way to know what’s safe
Minimum Goal: to find a USB switch that is tested, vetted, or can otherwise be proven secure
Optimum Goal: a “dumb” USB switch. Switching is performed at Layer 1 - mechanically & electrically. No CPU, no firmware, no attack surface. Basically just a mechanical relay between USB buses
Okay, what about the HID peripherals you are already trusting, the keyboard and mouse, that are essentially black box USB devices with microcontrollers and firmware with direct access to your input stream, operating system, and boot initialization process (BIOS/UEFI)?
Let’s assume those peripherals are already vetted
Then the logic is clear, acquire the same peripherals for the other setup instead of increasing attack surface with another black box in exchange for convenience.
I really want to be mad with this answer, but technically, yeah that’s the most secure setup 
Practically, I have no interest in juggling two physical keyboards, as I will need to switch back and forth quite frequently. Hence the USB switch: can that convenience be achieved securely?
No, any USB switch is an unvettable active bridge between both systems, which is inherently less secure than separate peripherals.
Well, there’s a risk of substantial risk, but it’s not a hopeless endeavor by any means
If I manually switch a trusted USB peripheral between USB ports on different machines, there is no risk, no active bridge between machines, no attack surface
Same thing if I hire someone to do exactly that at the push of a button. Or replace the man with a robotic arm. Or just a mechanical relay
We could probably build one pretty cheaply. Peripherals on a USB bus. Tie them together with a USB hub controller IC. Switch between two outputs with a MUX IC. Secure, simple, no issue
All I’m trying to do is find a preexisting commercial implementation. Im not the first OPSEC-minded person to want a USB switch - a friendly bird DM’ed me this resource, though this tool is no longer sold. Otherwise Ill build one & start retailing my implementation in a few months, I’ll offer pre-orders to PG
I tried to find something like this last year. At one point I ended up trying to just buy something from Amazon from a known brand (Anker). When I received the device and plugged it in, the thing registered as a billboard. I ultimately sent the device back and just manually swapped devices around as needed.
The problem is that there is no real way to vet these products without taking them apart and inspecting them properly. You would also need to splice open the USB cable itself to make sure it doesn’t have some tiny little controller used to capture and relay data to a third-party over cellular or something. To add insult to injury, it seems like most of these products are sold by relatively small companies based in China. While I don’t personally think every Chinese product is bad or malicious (I personally use Reolink and Gl.Inet stuff), you do have to be cautious.
If you have the ability and means to create your own simple device, that is honestly your best bet. Though, take my opinion with a grain of salt because I tend to be a little more on the paranoid side when it comes to devices. I won’t even use USB cables from Amazon unless they come from a very reputable vendor because I worry about the extremely unlikely chance of getting a malicious cable.