sha3-avr

A public domain implementation of SHA-3 on 8-bit AVR
microcontroller, just because you never know when you might need one!

Written by Markku-Juhani O. Saarinen markku@teserakt.io for Teserakt.

Prerequisites

In addition to basic things like make you will need (just apt install on
Debian/Ubuntu) at least the AVR compiler suite avr-gcc and avrdude if
you’re flashing a physical Arduino. Even though SHA3 or the test suite
doesn’t use any libraries at all (bare metal!), installing arduino-core
doesn’t hurt.

Assember vs C implementation

The Assember version of “Keccak” f1600 permutation is in f1600_avr.S and the C equivalent is in f1600_c.c. You can switch between the two by changing the object file name in Makefile.

You’ll see that, depending on compile flags, the Assembler version is about 2.5 to 5 times faster and 2 to 7 times smaller than the C version. The assembler permutation is about 1 kilobyte.

Full SHA3 and SHAKE API is provided by sha3.h and sha3.c. Note that for the assembler version the context needs to be aligned to 256 bytes. I recommend using the shared common_sha3_ctx rather than trying to get it from stack (or, worse still, via malloc()). In rare case where you need to run two hashes at the same time just add one at common_sha3_ctx.S. Since SRAM is scarse you can use that 256-byte scratch space for other purposes when not hashing.

The file test_sha3.c contains known-answer tests and you probably don’t want to include that (or the serial printing and benchmarking stuff) in your project.

Running on SIMAVR

If you don’t have an Arduino lying about, you can use
simavr (it’s packaged for latest Ubuntu and also available at
https://github.com/buserror/simavr) and test the code with make sim.

This cycle-perfect simulator simulates even the UART so the output will be
basically equivalent to real thing:

$ make sim
mkdir -p obj/
avr-gcc -Wall -Os -mmcu=atmega2560 -DF_CPU=16000000 -c f1600_avr.S -o obj/f1600_avr.o
(..)
simavr -v -v -v -m atmega2560 sha3-avr
Loaded 4042 .text at address 0x0
Loaded 1496 .data
UART: 0 configured to 0019 = 2403.8462 bps (x1), 8 data 1 stop
UART: Roughly 4576 usec per byte
test_sha3() = 00.
test_shake() = 00.
Run #00 145880 ticks / block.
Run #01 145864 ticks / block.
Run #02 145855 ticks / block.
^Csignal caught, simavr terminating

The two test zeros in the beginning meant that test vectors matched.
The ticks are for a full Keccak f1600 permutation (24 rounds).

Running on Arduino

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 Arduino Mega 2560
with Ubuntu 18.04.

$ make flash
avrdude -v -c wiring -p m2560 -P /dev/ttyACM0 \
        -U flash:w:sha3-avr.hex -D
avrdude: Version 6.3

.. more stuff.. and then the interesting bit:

stty -F /dev/ttyACM0 raw icanon eof \^d 38400
cat < /dev/ttyACM0
test_sha3() = 00
test_shake() = 00
Run #00 145880 ticks / block
Run #01 145864 ticks / block
Run #02 145855 ticks / block
Run #03 145851 ticks / block
Run #04 145850 ticks / block
Run #05 145848 ticks / block

Intellectual property

See LICENSE for license details (it’s unlicense, essentially free).