Sigmajoin
Sigmajoin is a next-generation privacy protocol for UTXO-based blockchains. Building on ZeroJoin, it introduces non-interactive, outsourceable mixing and enhanced privacy features for scalable, flexible, and user-friendly coin mixing.
What is Sigmajoin?
Sigmajoin is a privacy protocol designed for UTXO-based blockchains, enhancing user anonymity. It builds on ZeroJoin (the protocol behind ErgoMixer), introducing non-interactive, outsourceable mixing, improved scalability, and flexible fee handling.
Example: Outsourceable Mixing
With Sigmajoin, mixing can be outsourced to a third-party service ("mixer") in a trustless manner. Mixers cannot steal funds, and users benefit from stronger anonymity and easier fee handling.
ZeroJoin vs Sigmajoin
| Aspect | ZeroJoin (ErgoMixer) | Sigmajoin |
|---|---|---|
| Proofs Used | Proofs of knowledge of Diffie-Hellman tuples | Proofs of knowledge of Diffie-Hellman tuples |
| Interaction Level | Partially Non-interactive: Requires online presence for remixing | Non-interactive |
| Outsourceability | No, mixing cannot be outsourced | Yes, mixes can be outsourced to third-parties |
| Types of Boxes | 2 (Half-Mix and Full-Mix): Limited scalability | More than 2: Better scalability, half-mix boxes eliminated |
| Stealth Withdraw | Supported | Supported |
| Fee Handling | Embedded Fee: Included in mix boxes | Outsourced Fee: Paid by third-party mixer |
How Sigmajoin Works
- Deposit: Users deposit coins into a special pool as mix-boxes (fixed denominations).
- Mix: A third-party service or another user selects any two mix-boxes from the pool and mixes them. After mixing, two new mix-boxes are added back to the pool, concealing original ownership.
- Withdraw: Users can withdraw their coins from the pool at any time.
Steps for Mixing Boxes
- Select Two Boxes: Choose any two mix-boxes from the pool.
- Re-randomise Public Key: Perform a mathematical operation on the registers a and b of each selected mix-box.
- Validation: Prove that the operations were done correctly. The new mix-boxes should look identical to an observer.
For technical details and mathematical proofs, see the Sigmajoin Whitepaper.
Outsourceability
Mixing can be outsourced to a third-party service ("mixer") in a trustless manner. Mixers cannot steal funds, and users benefit from stronger anonymity and easier fee handling.
Outsource MixStealth Withdraw
Sigmajoin allows transactions that appear to be mixes but are actually withdrawals, making it even harder to trace transactions and enhancing privacy.
Stealth TransferOutsourced Fee
Mining fees can be paid by third-party mixers, simplifying the process for users and adding flexibility to the protocol.