For now this is just a basic one-time pad (OTP) implementation in C, described below.
This will be disguised in a larger program where it can be plausibly denied to be a deliberate one-time pad.
The README in docs describes the planned "cover" functionality.
Once built (make), simply run otp messagefile keyfile newkeyfile.
Output is to stdout and the unused portion of the key is written to newkeyfile.
So if messagefile is 100 bytes long and keyfile is 500 bytes then otp messagefile keyfile newkeyfile will write the last 400 bytes of keyfile to newkeyfile.