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Umbra Cash
About
A stealth-address payment protocol that hides the recipient behind a fresh address for every transfer.
About
A stealth-address payment protocol that hides the recipient behind a fresh address for every transfer.
Umbra Cash is a stealth-address payment protocol. A recipient registers separate viewing and spending public keys, and a sender uses them to derive a fresh address that only the recipient can control. The sender transfers ETH directly to that address or routes an ERC-20 payment through the immutable Umbra contract, which emits the encrypted data the recipient needs to discover the payment. Recipients scan Announcement events with their viewing key and use their spending key to access payments intended for them.
Privacy considerations
Umbra is not a mixer and does not use zero-knowledge proofs or an anonymity pool. The sender, amount, token, and fresh receiving address remain public. Privacy comes from hiding the identity of the person controlling that address.
Although not enforced by the protocol, Umbra Cash users register their public keys on StealthKeyRegistry. On one hand, this allows stealth transfers between the sender and the recipient without exchanging any data offchain. On the other hand, stealth transfer recipients are very likely to be among the registered addresses, which reduces recipient anonymity set.
2025 Aug 03 — 2026 Aug 03
Asset | Deposits 7D | Deposits 30D | Deposits Total | Value Locked |
|---|---|---|---|---|
 DAI | 1 $9.99 K | 3 $31.94 K | 173 $804.10 K | — |
 ETH | 0 $0.00 | 104 $1.24 M | 23.33 K $106.35 M | — |
 USDC | 0 $0.00 | 10 $103.90 K | 682 $4.23 M | — |
 USDT | 0 $0.00 | 2 $509.58 | 623 $6.08 M | — |
 WBTC | 0 $0.00 | 0 $0.00 | 162 $11.22 M | — |
| Total | 1 $9.99 K | 119 $1.37 M | 24.97 K $128.70 M | $0.00 |
Funds can be lost if
- an unsupported ERC-20, such as a fee-on-transfer or rebasing token, causes the Umbra contract’s internal accounting to diverge from its token balance.
Privacy can be lost if
- a recipient sends funds from a stealth address to a publicly linked address or consolidates payments in a recognizable way.
- public timing, amount, token, or ENS registration patterns let an observer narrow down the possible recipient.
New payments can be stopped if
- the Umbra owner sets an arbitrarily high toll for contract-routed payments.
Umbra has no governance process or contract upgrade mechanism. The Umbra and StealthKeyRegistry contracts are immutable.
The Umbra contract has a permissioned owner that can immediately set the ETH toll charged on every contract-routed payment and change the addresses that collect and receive those tolls. Because the toll has no upper bound, the owner can effectively stop new payments through the Umbra contract at any time. The owner cannot change the payment or withdrawal logic and cannot prevent recipients from accessing payments already sent to them, so the exit window is infinite and the protocol passes the walkaway test.
Transparent setup
Detailed description
Transparent proving systems require no trusted setups and have no additional setup-related trust assumptions.
Ethereum
Actors:
- Can interact with Umbra
- set an arbitrary ETH toll that must be paid on every transfer routed through the Umbra contract
Ethereum
Public registry that maps an Ethereum address to its two secp256k1 stealth public keys: a spending key used to derive a fresh stealth address, and a viewing key used to encrypt the transfer metadata for the recipient.
Main entry point of the Umbra protocol, routing all ETH and ERC-20 stealth payments. On send, it emits an Announcement event that the recipient scans to detect the payment. ETH is forwarded directly to a fresh stealth address, ERC-20s are escrowed in this smart contract.
- Roles:
- owner: EOA 1