README.md


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Cryptech tamper detection
This is software for the Atmel AVR ATtiny828 MCU on the Cryptech alpha
board, rev02, implementing tamper detection and master key erasure.
Overview
   *************
   * P A N I C *
   *   button  *
   *************
    /
   /
  /
AVR ---- SPI mux ---- FPGA
            |          |
            |         ARM
           MKM

AVR -- Atmel MCU
FPGA -- FPGA
MKM -- Master Key Memory, 23K640 SRAM
SPI mux -- 2 x MC74AC244DW
ARM -- ARM CPU


The MKM holds the master key for the device.
The AVR, MKM and the mux are battery powered.
The AVR and the FPGA are sharing access to the MKM through the mux,
with the AVR connected to the pins used for deciding who's in control
of the memory. The FPGA is in control by default.
When the panic button is pressed, the AVR grabs the MKM and writes
zeros to it as quickly as possible. In idle mode, i.e. when the panic
button is not pressed, the AVR tries to consume as little power as
possible.
Building the software
To build a .hex file suitible for uploading to a board with a
ATTiny828, a C compiler for AVR is needed, as wells a objcopy. On a
Debian system, the following command can be used for installing both:
apt-get install gcc-avr binutils-avr


To build tamper.hex, type 'make' in this directory.
To upload a .hex file to a board, the program avrdude can be used. On
a Debian system, the following command can be used for installing
avrdude:
apt-get install avrdude


If configuration for ATtiny828 is missing, the file attiny828.conf in
this directory could be appended to avrdude.conf:
cat attiny828.conf >> /etc/avrdude.conf


Often, a piece of hardware often called an SPI programmer is needed in
order to upload the .hex file. The one I've been using has
"sparkfun.com" printed on it. This small board has a mini-USB port to
connect to a host system and a header with SPI pins to connect to a
board with an AVR on it.
To upload a .hex file to a board, use the upload.sh shell script in
this directory with the name of the file as the only argument:
./upload.sh tamper.hex


Depending on permissions on your host system you might want to run the
upload script as root.