I would like to attach a SRAM module to the RasPi.
My idea is to store sensitive (encrypted) data on the SD card but keep the key on a SRAM module. It would have its own backup battery (or supercapacitor) and an anti-tamper switch that would erase the contents if the enclosure was opened.
Is there any way to interface to the SRAM with only the 8 available GPIO lines?
The SRAM module itself would need a capacity of at least 128 bits (the size of the smallest AES key) but even a 1-bit wide memory would seem to require 7 address lines and one data line plus 2 or 3 control lines.
Can it be done? I am thinking it may be possible to cheat by reusing an I/O line that was designed for something else.