[Cryptography] Dumb idea: open-source hardware USB key for crypto

[Bill Stewart]

At 02:53 PM 1/10/2014, Bill Cox wrote:
>I've been noodling the idea of a USB stick designed in a way that we
>can trust the crypto that goes on there.  It's a hard problem, but
>there seems to be some guidelines that could help:

Ian Goldberg and others argued some years ago that you need to have
a display and keypad on the device, so you don't have to trust the computer
not to steal keys from the users (his solution was a Palm Pilot,
but a simple 2x16 LCD and some buttons will do.)

You'll need an independent power supply (even if it's just a 
wall-wart USB charger)
to help prevent some of the power-analysis attacks that smart cards 
are vulnerable to.

Depending on how paranoid you want to be, you may want the USB interface
to be on a separate chip, such as the fairly dumb FTDI chips used in 
the earlier Arduinos,
so that you're only handling data on the USB, not full programming,
and can restrict your paranoia to your JTAG interface.
Or you could choose to be a good bit less paranoid and
provide the programs on an SD card the way Raspberry Pi does instead of JTAG,
if your FPGA can read that (natively or with help from an AVR 
microcontroller/etc.)