05-Sep-16 Markku-Juhani O. Saarinen [email protected]
A public domain constant-time implementation of AES-256 on 8-bit AVR microcontroller, just because you never know when you might need one !
We implement block encryption only -- to get an encryption/decryption thing going, use CTR or similar. Note that inverse AES is much slower and cannot reuse the same components.
The actual assembly language implementation is in aes256enc.S, the
rest is just testing.
The flashing code is incorporated into Makefile. You need to install
(just apt install on Debian/Ubuntu) at least avr-gcc and avrdude
packages.
Plug Arduino into a USB port and do a make flash. Now the thing will compile
code, flash it, and dump output via UART with stty magic to your standard
output. Most relevant settings are in Makefile -- you should edit that
first if something fails. The default settings work with my stock Arduino Uno
(R3) with Ubuntu 16.04.
$ make flash
mkdir -p obj/
avr-gcc -Wall -Ofast -mmcu=atmega328p -DF_CPU=16000000 -c aes256enc.S -o obj/aes256enc.o
.. more stuff.. and then the interesting bit:
AES-256 Self-Test: OK
Run #00 5578 ticks / block
Run #01 5567 ticks / block
Run #02 5562 ticks / block
Run #03 5551 ticks / block
Run #04 5557 ticks / block
Run #05 5557 ticks / block
Run #06 5556 ticks / block
Run #07 5556 ticks / block
Run #08 5556 ticks / block
Run #09 5556 ticks / block
That's a success!
If you don't have an Arduino lying about, you can fetch
simavr (https://github.com/buserror/simavr) and test using it with
make sim.
This cycle-perfect simulator simulates even the UART so the output will be basically equivalent to above:
$ make sim
simavr -v -v -v -m atmega328p avr-aes256enc
Loaded 3914 .text at address 0x0
Loaded 566 .data
UART: 0 configured to 0019 = 2403 bps (x1), 8 data 1 stop
UART: Roughly 4587 usec per bytes
AES-256 Self-Test: OK.
TIMER: avr_timer_configure-0 TOP 3906.25Hz = 256 cycles = 256usec
TIMER: avr_timer_configure-1 TOP 0.06Hz = 16778290 cycles = 16778290usec
Run #00 5578 ticks / block.
Run #01 5567 ticks / block.
Run #02 5546 ticks / block.
Run #03 5559 ticks / block.
Run #04 5561 ticks / block.
Run #05 5557 ticks / block.
Run #06 5555 ticks / block.
Run #07 5555 ticks / block.
Run #08 5555 ticks / block.
Run #09 5555 ticks / block.
^Csignal caught, simavr terminating
Have fun.
Cheers, -markku
ABSOLUTELY NO WARRANTY WHATSOEVER