USB adapter devices and keylogging

[QuincyJones]

So, I was just having a thought, techically as the computer treats the usb device as the keyboard, maybe each keypress will be stored in the device's RAM for a certain amount of time which could then maybe be read somehow? No idea how many keypresses would be stored (if any at all). Not really a concern for most of you, but still interesting to think about.

Can anyone shed any more light on this?

[Findecanor]

Are you referring to storage in the keyboard's microcontroller or in the USB controller on the host?

Most cheap USB keyboards use an inexpensive off-the-shelf keyboard controller that is especially made for keyboards.
Firmware in more advanced keyboards have no need to store old key events: only the current key state and maybe a queue of events to send but even that is pushing it. Keyboard controllers are usually pretty simple, with very little RAM.

I would think that most USB controller hardware are very generic, with no special features for interface devices. There are some "for gaming" motherboards with special USB ports for mice or keyboards where devices are more or less guaranteed a fast polling rate -- but I would guess that that is more of a driver feature than anything.
The USB keyboard control is in drivers in the operating system - and those are often "class drivers" that could be used with any keyboard, unless a special driver has been installed for a particular model.

Because USB is not encrypted, it would of course be possible to make a device that is connected in-between the host and the keyboard that would be logging every key stroke. But it would not be possible to sniff key presses from another port.