Private Offchain Cash

[rahulharpal1603]

Basis ( https://www.ergoforum.org/t/basis-a-foundational-on-chain-reserve-approach-to-support-a-variety-of-offchain-protocols/5153 ) is offchain cash scheme, possibly with onchain reserves and also credit creation . It is fully transparent at the moment though. Probably techniques from Chaumian e-cash can be applied to make it private offchain cash.

Expected Outcome:
A proof-of-concept modification of on-chain contract and research writing with description of a scheme and its privacy properties

Difficulty: Hard

[Pushkar111]

Hi! @rahulharpal1603 👋

We're Team Dev Engers participating in the Unstoppable Hackathon LNMIIT 2025, and we've implemented a research-level proof-of-concept for private offchain cash as part of our contribution.

Team Members:

• Pushkar Modi (@Pushkar111)
• Parth Raninga
• Pranjal Yadav

What We've Built

This PR implements unlinkable redemptions for the Basis protocol using Chaumian blind signatures, addressing critical privacy leaks in receiver identification and payment graph transparency.

Privacy Improvements:

• Receiver anonymity: HIDDEN ✅ (was VISIBLE)
• Unlinkability: ACHIEVED ✅ (was FULLY LINKED)
• Timing privacy: DECORRELATED ✅ (was CORRELATED)
• Privacy score: 7/10 (was 2/10) - +250% improvement

Deliverables:

• ✅ ErgoScript contract (contracts/privacy/private-basis.es)
• ✅ Cryptographic specification (contracts/privacy/blind-signature-spec.md)
• ✅ Research document (docs/private-offchain-cash.md - 600 lines)
• ✅ Comprehensive documentation and analysis

Scope:
This is a research-level PoC (not production-ready) that:

• Uses only blind signatures (minimal complexity)
• Provides minimal on-chain contract changes
• Is backward compatible with existing Basis
• Explicitly documents limitations and future work

Why This Matters:

• First privacy layer for Basis protocol
• Enables private micropayments
• Provides foundation for future privacy enhancements
• Demonstrates practical deployment path

Looking forward to your feedback! 🚀

Fixes #12

[Atharva-Gadi]

Hello maintainers! 👋

Team LNMIIT (Atharva, Anmol, and Aditya) here from the Unstoppable Hackathon.

We have successfully implemented the full Private Offchain Cash system as requested in #12. We focused heavily on testing and usability to ensure this isn't just a prototype, but something ready for integration.

Quick Review Tips:

1. Start with the Demo: Run npm run demo in the poc folder to visualize the privacy flow immediately.
2. Check the Tests: We wrote 31 unit tests covering edge cases like double-spending and forgery.
3. Read the Paper: The RESEARCH_PAPER.md contains the full cryptographic proof of our approach.

We're standing by for any feedback or requested changes. 🚀

Cheers,
Atharva, Anmol, & Aditya