UMBRA

Umbra is a privacy-preserving dark pool for FAssets on the Flare Network.

Public blockchains publish every trade. Anyone can see what you hold, what you traded, and who you traded with — which is exactly the information that makes front-running and MEV extraction possible. Traditional dark pools solve the visibility problem by moving the order book inside a private venue you have to trust.

Umbra takes a third path: your balances and orders stay private, and the protocol proves — in zero knowledge, verifiable by anyone — that every settlement followed the rules.

What stays private

Depositing into the vault is a public ERC-20 transfer — there is nothing secret about putting money in. Everything you do inside the vault is private, and what you reveal on the way out depends on which exit you take.

Dark pool orders are the strongest case: amounts and assets stay hidden. The only public values are an opaque commitment and a nullifier.

How it works

1. Shield — deposit tokens into ShieldedVault. A commitment to your new note is inserted as a leaf in an on-chain Merkle tree. No proof is needed yet; you’re publishing a commitment, not spending one.

2. Trade — place an order by spending a note and inserting an opaque order commitment in its place. Orders rest off-chain in the dark engine’s book. A matcher pairs compatible orders and generates a zero-knowledge proof that the match was computed correctly.

3. Exit — settle to a new shielded note, pay someone privately, or withdraw publicly to an address.

Matching happens off-chain, but correctness is not a matter of trust: the match_orders circuit proves the fill respected both traders’ limits, and MatchOrdersVerifier checks that proof on-chain before the vault moves anything. A dishonest matcher cannot produce a valid proof for an invalid match.

Cryptography

Umbra’s note scheme is adapted from Tornado Cash’s commitment/nullifier pattern, extended for variable amounts and multiple assets rather than one fixed denomination.

• Noir circuits, compiled to WASM and proven in your browser with Barretenberg — except match_orders, which is proven by an off-chain worker.
• Poseidon2 for all commitments and nullifiers — a hash designed to be cheap inside an arithmetic circuit.
• Solidity verifiers generated per circuit, called by ShieldedVault.

Status

Umbra runs on the Flare Coston2 testnet. No real funds are at risk. See Deployed Contracts for live addresses, and Getting Started to make your first shielded deposit.