Cowrie Research

umbra

4 min read

Umbra

  • Name: Umbra
  • URL: https://app.umbra.cash/
  • Category: stealth-address payment protocol / recipient-privacy infrastructure / meta-transaction withdrawal middleware
  • Tags: ethereum-ecosystem
  • Summary: Umbra is recipient-privacy infrastructure for EVM payments: stealth addresses, announcement scanning, and relayer-aided withdrawal. Useful lower-bound privacy rail, not a mixer and not full transaction privacy.
  • What it does:
    • Lets users receive funds at fresh stealth addresses on EVM chains while remaining unlinkable to public recipient identities from the perspective of outside observers
    • Uses app-derived spending and viewing keys so senders can compute recipient-specific stealth addresses without interactive address exchange
    • Publishes encrypted randomness and announcement data that receivers can scan with a viewing key to identify transfers intended for them
    • Supports direct ETH delivery to stealth addresses and contract-held token delivery with later withdrawal by the recipient
    • Provides meta-transaction and relayer flows so token withdrawals do not require the stealth address itself to already hold ETH for gas
    • Exposes an SDK (umbra-js) so other apps can integrate key generation, sending, scanning, and withdrawal behavior
  • Key claims:
    • The official README repeatedly says Umbra is a stealth address protocol for EVM networks and explicitly contrasts it with mixers: the sender remains public, but the receiver’s identity is obscured because the funds land at a fresh address that outsiders cannot link back to the recipient.
    • The README’s seven-step walkthrough shows the core split clearly: users derive spending and viewing keys from a signed message, publish the public keys, senders generate a stealth address using the spending key and random number, the random number is encrypted with the viewing key, and the receiver scans announcement events to recover matching payments.
    • The README emphasizes that Umbra does not provide “full” privacy like Aztec or Zcash. That limitation is useful, not disqualifying: it makes Umbra a clean lower-bound comparison for recipient privacy without privacy-preserving amount, sender, or asset-source obfuscation.
    • The umbra-js README explains a crucial operational design choice: ETH can be sent directly to the stealth address, but tokens are instead held by the contract because a token-only stealth address would otherwise lack ETH to pay gas for withdrawal. This contract-holding and relayer pattern is a major part of Umbra’s real control surface.
    • The same SDK docs say users can separate spending and viewing keys, allowing third-party scanners to detect incoming transfers without being able to spend them. That makes Umbra more than an address trick; it is also scanning and notification middleware.
    • The SDK docs describe withdrawOnBehalf() and a default relayer, showing that recipient privacy UX depends partly on meta-transaction infrastructure and whoever operates or substitutes for the relay path.
    • ERC-5564 is not Umbra documentation, but it is an important adjacent standard in this pass because it codifies a singleton announcer contract, spending/viewing key vocabulary, and non-interactive stealth-address interfaces that closely match the control surfaces Umbra helped make legible.
    • The strongest comparison frame is therefore not “privacy app” but “stealth-address recipient-privacy rail with relayer-aware withdrawal design.”
  • Whitepaper: No canonical standalone Umbra whitepaper or litepaper surfaced in this pass. The clearest primary materials were the official app FAQ, the repository README, and the umbra-js SDK README; ERC-5564 is also a useful adjacent standard for situating the mechanism; see ../whitepapers/umbra-primary-sources-2026-05-11.md.
  • Sources:

Internal linkages

  • Best mechanism baseline: erc-5564.
  • Best broader privacy contrast: railgun.
  • Keep the note on recipient privacy, announcement scanning, and relayer-dependent withdrawal, not on generic privacy app bundling.

Control surface

  • Practical control sits in announcement scanning, viewing-key handling, relayer availability, contract-held token withdrawal, and which wallet or service runs the recipient-discovery path.

  • Umbra is small but useful because it makes the stealth-address rail visible without pretending to solve full transactional privacy.

  • Last reviewed: 2026-06-10 UTC

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