https://github.com/urish/ctf-shittyaddon
Capture The Flag Shitty Addon
https://github.com/urish/ctf-shittyaddon
arduino attiny85 avr capture-the-flag challenge ctf kicad pcb-design shittyaddon
Last synced: 7 months ago
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Capture The Flag Shitty Addon
- Host: GitHub
- URL: https://github.com/urish/ctf-shittyaddon
- Owner: urish
- License: mit
- Created: 2019-08-27T14:33:04.000Z (about 6 years ago)
- Default Branch: master
- Last Pushed: 2019-11-02T20:18:37.000Z (almost 6 years ago)
- Last Synced: 2025-01-11T19:32:55.334Z (9 months ago)
- Topics: arduino, attiny85, avr, capture-the-flag, challenge, ctf, kicad, pcb-design, shittyaddon
- Language: C++
- Size: 27.3 KB
- Stars: 10
- Watchers: 3
- Forks: 3
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
- License: LICENSE
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README
# Minimal Shitty Add-On with Capture The Flag Challenge
Copyright (C) 2019, Uri Shaked. Released under the MIT license.
[__Learn more in the blog post: Capture The Flag Shitty Add-On__](https://blog.wokwi.com/capture-the-flag-shitty-add-on/?utm_source=github)
## Hardware
The [ctf-shittyaddon board](pcb/) includes the following hardware:
1. ATtiny85 Processor
2. A [ShittyAddon V1](https://twitter.com/MrRobotBadge/status/962043056781324289) connector
3. Reset button
4. Red LED connected to ATtiny85's pin 6 (PB1)
You can also hack a simplified version on a breadboard:
## Firmware
Compile the firmware using the Arduino IDE:
1. Install [ATTiny Core](https://github.com/damellis/attiny)
2. Install the [TinyWire Library](https://github.com/lucullusTheOnly/TinyWire)
3. Configure Arduino IDE as follows:
- Board: ATtiny25/45/85
- Processor: ATtiny85
- Clock: Internal 8 MHz
4. Set the fuses of the chip to enable self programming (`SELFPRGEN=1`).
This can be done using `avrdude`:
```bash
avrdude -pattiny85 -cusbtiny -e -Uefuse:w:0xfe:m -Uhfuse:w:0xdf:m -Ulfuse:w:0xe2:m
```
When building your own firmware, replace `SECRET` in the string `"$FLAG:SECRET"`
with your secret value (the flag).
## The Challenge
The [firmware code](ctf-firmware/ctf-firmware.ino) implements an I2C slave listening on address 0x23.
The challenge consists of several milestones of increasing difficulty:
1. Make the red LED light
2. Find the secret flag value (it starts with the string "$FLAG:")
3. Make the red LED blink by executing code directly on the ATTiny85
4. Replace the secret flag with a new value without bricking the board
All the above milestones can be achieved through I2C communication with
the chip.
For more information, [check out the blog post](https://blog.wokwi.com/capture-the-flag-shitty-add-on/?utm_source=github)