Digispark Mini, ATtiny85, USB

The ATtiny85 is an arduino compatible microcontroler with an included USB port.

The publisher Heise estimates the hazard potential as high.

In short, that's our chip.

• Downlaod Arduino IDE for your OS
• if nessesary, unpack downloaded file
• run installer

• open Arduino IDE
• Select menu: “Datei-Voreinstellungen”
• Add to “Zusätzliche Bordverwalter-URLs:” the line http://digistump.com/package_digistump_index.json

The IDE downloads the source code.

* Select menu: "Werkzeuge-Board:*-Digispark (default - 16mhz)

* You see the error on upload: micronucleus: ''library/micronucleus_lib.c:63: micronucleus_connect: Assertion `res >= 4' failed'' 
  * permission problem on USB: start it as root

• Dokumentation 1, Documentation 2

          __________
         |         o| P5  : D5,A0
    _____|         o| P4  : D4,A2,PWM4,USB-
   |               o| P3  : D3,A3,USB+
   |USB            o| P2  : D2,A1,SCK,SCL
   |_____          o| P1  : D1,PWM1,MISO
         |         o| P0  : D0,PWM0,AREF,MOSI,SDA
         |_o__o__o__|
          5V GND VIN
          
     D:Digital IO,A:Analog I
     AREF: Analog Reference
     PWM: Puls width modulation, Analog O
     USB-,USB+: USB Port
     SDA,SCL: I2C
     MOSI,MISO,SCK: SPI

• 8K Flash (6K +Bootloader)

• Select menu: “Datei-Beispiele-Digispark_Example-Start”

test1.sketch

void setup() {                
  pinMode(0, OUTPUT);
  pinMode(1, OUTPUT);
  }
void loop() {
  digitalWrite(0, HIGH);
  digitalWrite(1, HIGH);
  delay(1000);
  digitalWrite(0, LOW);
  digitalWrite(1, LOW);
  delay(1000);
  }

• Press on german tastatur WIN+Y (here WIN+Z) which open context menu (individual Openbox 3 specification)
• Press ENTER open a terminal (individual Openbox 3 specification)
• Type echo Hello World! followed by ENTER
• terminal execution of echo Hello World! prints Hello World!

The BadUSB stick executes echo by inserting into USB port. The problem is an execution of malicious code by inserting a simple USB stick.

badusb2.sketch

#include "DigiKeyboard.h"
void setup() {
  pinMode(0, OUTPUT);
  pinMode(1, OUTPUT); }
void loop() {
  digitalWrite(1, HIGH);
  DigiKeyboard.delay(5000);
  DigiKeyboard.sendKeyStroke(0);
  digitalWrite(0, HIGH);
  DigiKeyboard.sendKeyStroke(KEY_Z,MOD_GUI_LEFT);
  DigiKeyboard.delay(1000);
  DigiKeyboard.sendKeyStroke(KEY_ENTER);
  DigiKeyboard.delay(1000);
  DigiKeyboard.println("echo Hello World!");
  digitalWrite(0, LOW);
  digitalWrite(1, LOW);
  DigiKeyboard.delay(10000);
}

• Key definitions by Digispark
• USB HID for FreeBSD

• Send 0 if Pin0 is GND else send 1 via SerialUSB
• Read on PC via cat /dev/ttyACM0

notaus1.sketch

#include <DigiCDC.h>

void setup() {
  SerialUSB.begin();
  pinMode(0,INPUT);
  digitalWrite(0, HIGH);
}

void loop() {
  SerialUSB.print(digitalRead(0),DEC);
  SerialUSB.delay(1000);
}

• Sketch compile by menu “Sketch-Überprüfen/Kompilieren”

The order is important:

• First: menu “Sketch-Hochladen”
• Then: put ATtiny85 into USB port

Background: AFAIK the ATtiny85 check for a new sketch while booting. If no new sketch loeaded, ATtiny85 use the flashed sketch.

The first flash was ok, the second flash was problematic. After the first flash I get an error: * micronucleus * res >= 4 *

Adding the following udev rule and save it as /etc/udev/rules.d/49-micronucleus.rules.

49-micronucleus.rules

# UDEV Rules for Micronucleus boards including the Digispark.
# This file must be placed at:
#
# /etc/udev/rules.d/49-micronucleus.rules    (preferred location)
#   or
# /lib/udev/rules.d/49-micronucleus.rules    (req'd on some broken systems)
#
# After this file is copied, physically unplug and reconnect the board.
#
SUBSYSTEMS=="usb", ATTRS{idVendor}=="16d0", ATTRS{idProduct}=="0753", MODE:="0666"
KERNEL=="ttyACM*", ATTRS{idVendor}=="16d0", ATTRS{idProduct}=="0753", MODE:="0666", ENV{ID_MM_DEVICE_IGNORE}="1"
#
# If you share your linux system with other users, or just don't like the
# idea of write permission for everybody, you can replace MODE:="0666" with
# OWNER:="yourusername" to create the device owned by you, or with
# GROUP:="somegroupname" and mange access using standard unix groups.

Run command udevadm control –reload-rules.