Z-Transfer — Decentralized File Sharing on 0Chain

Overview​

Z-Transfer is a file-sharing application that leverages the 0Chain (Zero Chain) decentralized storage blockchain to provide secure, censorship-resistant file hosting. Users upload files through a Bootstrap 5 web interface; the application shards the files using Reed-Solomon erasure coding and distributes them across multiple storage nodes (blobbers) on the 0Chain network.

The project includes a custom zero_sdk Python library — a complete SDK for interacting with the 0Chain blockchain, handling wallet management, storage allocation, file sharding, and BLS cryptographic signing. Signatures are generated via a Node.js sidecar using bls-wasm on the BN254 elliptic curve.

Key Features​

• Decentralized file storage: Files are erasure-coded (4 data + 2 parity shards) and distributed across multiple blobber nodes on the 0Chain blockchain
• Custom blockchain SDK: zero_sdk — a complete Python library for 0Chain interaction including Wallet, Allocation, Network, and ConnectionBase classes
• BLS cryptographic signing: BN254 curve signatures via a Node.js bls-wasm subprocess bridge, with a Heroku fallback endpoint
• File lifecycle management: Upload (shard, distribute, commit), download (reassemble from shards), and allocation management
• Docker Compose dev/prod environments: Development with Flask hot-reload on SQLite; production with Gunicorn + PostgreSQL + Nginx
• Responsive Bootstrap 5 UI: Jinja2 server-rendered templates with Font Awesome icons and vanilla JavaScript file upload with progress tracking
• Email notifications: Flask-Mail integration with SMTP for sender/recipient notifications

Architecture​

A three-tier containerized architecture with a custom blockchain SDK:

┌──────────────────────────────────────────┐
│              Nginx :80                   │
│         (prod reverse proxy)             │
└──────────────┬───────────────────────────┘
               │
┌──────────────▼───────────────────────────┐
│         Flask App (services/web/)        │
│  / ──── upload form (Jinja2 + Bootstrap) │
│  /upload-files ──── POST handler         │
│   ├── saves to uploads/                  │
│   └── emails sender/recipient            │
└──────────────┬───────────────────────────┘
               │ uses
┌──────────────▼───────────────────────────┐
│       zero_sdk (app/zero_sdk/)           │
│  Wallet ── balance, sign, restore        │
│  Allocation ── upload_file, download_file │
│  Network ── miner/sharder discovery      │
│  ConnectionBase ── consensus engine      │
└──────────────┬───────────────────────────┘
               │ signs via
┌──────────────▼───────────────────────────┐
│   JS Bridge (lib/bn254_signature_js/)    │
│   bls-wasm ── BN254 BLS signatures       │
└──────────────────────────────────────────┘

Tech Stack​