This repo contains all the code and documentation for team scriptohio from The Ohio State University in MITRE's eCTF 2025.
Highlights of our design:
- 🔐 Strong cryptography
- 💃 The Salsa20 stream cipher is used for lightning quick symmetric encryption and decryption
- 🌲 Our binary hash key derivation tree efficiently compresses unique keys per timestamp to create a subscription over a time interval 🕐
- 📝 All frames are signed and verified with Ed25519 to ensure decoders only read frames from the encoder they came from
- ⚡ Written in Zig
- 📦 Expansive standard library which includes everything a programmer might need, from string manipulation to secure cryptography
- 🧪 Unit testing framework built in, allowing for critical sections to have their correctness verified
- 🚫 Memory safety protections against common issues like indexing out of bounds, double free, integer overflows, and more
- 🚧 Build system with incredible interoperability with C code. We still use the MSDK, and there are no HAL rewrites in sight 👀
| Icon | Description |
|---|---|
| 👥 | Created by our team |
| 👔 | Created by MITRE for the competition, and unmodified by us |
- 👥
benches/- Custom benchmarks to test the speed of the design 🐍 - 👥
decoder/- Firmware for the decoder ⚡ - 👥
design/- Host design including encoder 🐍 - 👥
docs/- Documentation on the system design and security 📖 - 👔
tools/- Host tools to interact with the decoder 🐍 - 👥
Taskfile.yml- Command runner definitions 📄 - 👥
flake.nix- Convenient Nix development environment ❄️
A Taskfile is available to easily run common tasks
* 1-gen-secrets: Generate secrets
* 2-build-firmware: Build the firmware image
* 3-flash: Flash the built firmware image onto the Decoder
* 4-gen-subscription: Generate a subscription
* 5-subscribe: Take a subscription file and send it to the Decoder
* 6-list: Asks the Decoder to list the subscriptions that it currently has
* 7-uplink: Encodes sample frames with the custom encoder function and sends them to the satellite
* 8-satellite: Broadcasts all frames received from the uplink to all listening TVs on the host computer
* 9-tv: Receives encoded frames from the satellite and decodes with a Decoder connected to the host computer
* bench-decoder: Benchmark the decoder
* bench-encoder: Benchmark the encoder
* bench-subscription: Benchmark creating a subscription on the decoder
* docs: Build documentation design file into PDF and SVG artifacts
* stress-decoder: Use MITRE's stress test to benchmark the decoder
* stress-encoder: Use MITRE's stress test to benchmark the encoder
On a clean repo, plug in the MAX78000, enter firmware writing mode (the LED should be flashing blue), and run the following command:
task 1-gen-secrets 2-build-firmware 3-flash 4-gen-subscription 5-subscribe 6-list
Then, iterating on the design is typically done with the following command:
task 2-build-firmware 3-flash
The design document is available to read as a PDF, or inline below:
View the PDF inline
Our Zig code makes use of documentation comments which can be read as a webpage. To view it, navigate to the decoder directory and run the following
$ zig build docs
$ python -m http.server -d docs
Then navigate to http://localhost:8000 in your browser.
