[Cryptography] Understanding state can be important.

[Henry Baker]

At 01:31 PM 12/29/2015, Arnold Reinhold wrote:
>My solution to the write-protect problem involves two single purpose devices.
>
>One is a board that would serve as a write-protect shield for an SD card.
>
>All SDcards implement a Serial Peripheral Interface Bus (SPI), which is supported on the Arduino and R Pi platforms.
>
>The SDcard specs, e.g. http://blog.chinaaet.com/282280072/p/17750, include a set of commands.
>
>There are two for writing blocks: CMD24 and CMD 25.
>
>The wedge board would send commands and data to and from the SDcard transparently except that it would block the Write commands.
>
>This feature might be controlled by a switch or a jumper on the board.
>
>A light or sound alert could warn of a write attempt.
>
>The write-protect board with an SDcard installed might be made to act like a USB flash drive.
>
>This should be easy to do on a Raspberry Pi Zero ($5 retail), using the Pi Zero's USB port.

I'd be happy with a *true* "USB condom"; one that MITM'd the USB port and made damn sure that a passive memory device acted like a *single* *passive* memory device, and not a keyboard/mouse/whatever; it would also watch out for any changes in its VID/PID.

This same device could also ground any write commands.

I've seen some cheap devices that could conceivably do this, but the manufacturer would have to allow me reprogram the firmware.