🔒 Offline Digital Cash System with Dual Signatures
Concept: Enable secure offline peer-to-peer transactions using pre-signed digital tokens that can be transferred and redeemed without constant internet access.
🧠 How It Works
- Token Generation (Online)
- Users request tokens (₹1, ₹2, ₹5...) from the server.
- Tokens include: amount, sender_id, expiry, transaction_id
- Server signs with a private HMAC key
- Tokens are stored encrypted on device
- Offline Transfer
- Sender scans receiver's QR (containing receiver_id, HSN)
- Token is embedded with receiver info
- Signed locally using sender’s device key (HSN)
- Shared via QR/Bluetooth/NFC
- Online Redemption
- Receiver uploads token to server
- Server verifies both signatures (server + sender)
- Checks expiry, uniqueness, and binds it to receiver
- Token is marked as redeemed
- Amount is credited
🔐 Security Highlights
- 🔑 Dual Signature: Server + Local HSN binding
- 🧾 Tamper-proof and one-time redeemable
- 🕹️ Works offline for transfer; only receiver needs to be online for redemption
- 🔍 Tokens traceable but anonymous in transit
💰 Why It’s Like Cash Just like handing over a signed banknote:
- ✅ Fixed denomination
- ✅ Physically transferable
- ✅ One-time use
- ✅ Tamper-proof
© 2025 Debasis Sikdar. All rights reserved.
This repository and its contents are licensed under the Creative Commons Attribution-NonCommercial 4.0 International License.
You may share and adapt the materials with proper attribution, but commercial use is strictly prohibited without prior written permission.
🔒 Unauthorized commercial usage or rebranding will be subject to takedown notices and legal action under applicable IP laws.
License details: CC BY-NC 4.0