Umbra primary sources — 2026-05-11

Project status in this pass

• No canonical standalone Umbra whitepaper or litepaper surfaced.
• The clearest primary materials were the official app FAQ, the repository README, and the umbra-js README.
• ERC-5564 was also useful as an adjacent standard because it codifies many of the same control surfaces: stealth meta-addresses, viewing/spending keys, and singleton announcement infrastructure.

Primary-source snapshots

1) Official protocol framing

• URL: https://raw.githubusercontent.com/ScopeLift/umbra-protocol/master/README.md
• Key excerpt:
  • The README says Umbra is a stealth address protocol for EVM networks where a payer sends funds to a fresh address controlled by the intended receiver, but only the payer and receiver know that linkage.
  • This is the clearest reason to catalog Umbra as recipient-privacy infrastructure rather than as a mixer or wallet.

2) Explicit privacy boundary: not a mixer

• URL: https://raw.githubusercontent.com/ScopeLift/umbra-protocol/master/README.md
• Key excerpt:
  • The README says Umbra is not a mixer and does not use zero-knowledge proofs. Instead it makes the sender-to-recipient link hard to interpret because the receiving address has never been seen on-chain.
  • This matters because it clarifies Umbra’s exact privacy promise and its limits.

3) Core seven-step mechanism

• URL: https://raw.githubusercontent.com/ScopeLift/umbra-protocol/master/README.md
• Key excerpt:
  • The README describes a seven-step flow: derive spending/viewing keys from a signed message, publish public keys, generate a stealth address with a random number, encrypt that random number with the viewing key, emit the stealth address and encrypted random number in an announcement, scan announcements with the viewing key, and withdraw with the stealth private key.
  • That walkthrough makes the underlying control surfaces legible: key publication, announcement scanning, and withdrawal.

4) ETH-vs-token handling and why the contract holds tokens

• URL: https://raw.githubusercontent.com/ScopeLift/umbra-protocol/master/umbra-js/README.md
• Key excerpt:
  • The SDK README says ETH is sent directly to the stealth address, but tokens are held by the contract because a token-only stealth address would otherwise lack ETH for gas.
  • This is one of the most analytically important details in the pass because it means Umbra is not only a cryptographic addressing scheme; it also introduces contract custody and withdrawal middleware for token UX.

5) Meta-transactions and relayer dependence

• URL: https://raw.githubusercontent.com/ScopeLift/umbra-protocol/master/umbra-js/README.md
• Key excerpt:
  • The SDK documents withdrawOnBehalf() and relayWithdrawOnBehalf() so relayers can submit withdrawals for recipients.
  • That creates a practical trust and availability surface above the core cryptography.

6) Separate viewing and spending keys

• URL: https://raw.githubusercontent.com/ScopeLift/umbra-protocol/master/umbra-js/README.md
• Key excerpt:
  • The SDK explains that users can separate viewing and spending keys so third-party scanning services can identify incoming payments without gaining spending power.
  • This is important because it reveals a second layer of infrastructure: scanning, notification, and outsourced monitoring.

7) Standard-adjacent framing through ERC-5564

• URL: https://eips.ethereum.org/EIPS/eip-5564
• Key excerpt:
  • ERC-5564 defines stealth meta-addresses, viewing/spending key vocabulary, and a singleton announcer contract for non-interactive stealth-address transfers.
  • Even though the EIP is not Umbra product documentation, it is useful context because it turns Umbra-like recipient-privacy mechanics into a comparison-ready standard surface.

Working conclusion

Umbra is best cataloged as a stealth-address recipient-privacy rail with a meaningful operational wrinkle: token privacy UX depends on contract-held withdrawals and relayer support, not just on stealth addressing itself. That makes it a good baseline for later comparison against ERC-5564 tooling, wallet-integrated stealth-address UX, and other recipient-privacy systems.