BOOM (Barter Offline Over Mesh)

Inspiration

In a post-apocalyptic world without internet, governments, or trustworthy currency, survivors rely on cautious, local barter to meet their basic needs. We imagined a scenario where humanity's survival hinges on hyperlocal trades and trust built through consistent interactions.

Inspired by dystopian stories and the potential vulnerabilities of centralized networks, we envisioned BOOM: an entirely decentralized, Bluetooth-based barter network. We wanted to create something dark, immersive, and genuinely useful—where users must navigate risky interactions carefully, building or breaking trust in every exchange.

What it does

BOOM is a hyperlocal barter network app designed exclusively for iOS. It operates entirely offline, leveraging only Bluetooth (CoreBluetooth) to facilitate secure, anonymous trades between survivors.

Every user in BOOM is represented by a temporary rotating public identity key linked exclusively to their own device. Users only learn someone’s trustworthiness or reputation if they've traded with or tagged them before—significantly reducing impersonation and enhancing safety.

The app includes:

A secure local login system using unique device-generated IDs
Inventory management for tracking personal resources (e.g., food, batteries, medicine)
Bluetooth-powered discovery of nearby survivors with matching trade needs
Trust-building tools allowing users to log and tag past trade interactions
A dark, immersive UI themed in grey, black, and eerie green, echoing a haunting post-apocalyptic atmosphere

How we built it

BOOM was built entirely in Swift and SwiftUI, leveraging Apple’s CoreBluetooth framework for seamless offline device communication.

We intentionally avoided using any backend infrastructure—there's no cloud, no server, and no internet. All user data is stored securely on-device, using a combination of Core Data and UserDefaults.

Key technical features:

CoreBluetooth powers device scanning, advertising, and direct data transmission
JSON-encoded trade requests are securely sent over Bluetooth without pairing
SwiftUI provides a responsive, atmospheric UI optimized for low-light conditions

The rotating public key system was designed to provide security and anonymity without needing centralized verification.

Challenges we ran into

🧩 Bluetooth Trade Exchange: Handling peer-to-peer Bluetooth communication reliably with CoreBluetooth was a major hurdle. We debugged and tested trade flows between real iPhones under real-world offline conditions.
🔐 Local Identity & Security: Creating a rotating device identity system that preserves anonymity but prevents impersonation was a complex design challenge.
🎨 Thematic UI: Delivering a deeply immersive, horror-inspired interface with SwiftUI while ensuring functionality and accessibility required several design iterations.

Accomplishments that we're proud of

🚀 Built a fully offline peer-to-peer barter system
🛡️ Designed a working rotating key identity system for anonymity and trust
📡 Achieved secure Bluetooth data transfer between iPhones with no pairing
🌒 Created a custom, horror-themed UI that reflects the post-apocalyptic vibe
🔄 Enabled two-way trade tracking with reputation tagging

What we learned

Learned how to integrate CoreBluetooth for iOS device-to-device discovery, advertisement, and data transfer
Gained experience with local-only data storage using Core Data and secure hashing
Deepened understanding of how to create secure and anonymous systems that work offline
Improved team skills in building cohesive UI/UX in SwiftUI
Developed strategies to simulate real-world trust dynamics in technology systems

What's next for BOOM

🛠️ Improve trade protocol reliability over Bluetooth (with retries, acknowledgments)
🌐 Add support for multi-device group trades or chain trades
💬 Refine the trust and tag system to support richer reputation tracking
🔐 Integrate optional cryptographic signing and encrypted trade history
📱 Publish a full open-source version for use in real-world disaster scenarios or festivals