Selective Disclosure in Zcash

Key Facts

• A viewing key can reveal transaction information but cannot spend ZEC.
• Incoming and full viewing keys expose different directions and scopes.
• A broad viewing key is not the same as a one-transaction receipt.
• ZIP 311 payment disclosures are a draft specification, so wallet support must be verified.

Private by default does not mean impossible to verify

Public blockchains make verification easy by publishing everybody's financial activity. Zcash takes a different route: shield the transaction details first, then give the user tools to disclose information when there is a legitimate reason.

That difference matters for payroll, donations, accounting, audits, and payment disputes. The goal is not secrecy without accountability. It is avoiding permanent public disclosure to the entire internet when one accountant, donor, merchant, or counterparty needs evidence.

Viewing keys provide scoped read access

A viewing key is a cryptographic read credential. It does not contain spending authority, but it can let compatible software scan the chain for shielded activity associated with an account or receiver. The resulting visibility can include amounts, memos, diversified recipient addresses, and whether known notes were later spent, depending on the key type and protocol.

Incoming viewing capability is narrower: it is intended to detect payments received. A full viewing key can expose both received and spent activity for its scope. Unified viewing keys can package viewing capabilities across several Zcash receiver types. Those distinctions are the reason a request for 'the viewing key' is dangerously vague.

Choose the smallest disclosure that answers the question

If an accountant needs continuing visibility into a business account, a full viewing key may fit the job. If a donor wants to prove one transfer, account-wide visibility is excessive. A screenshot or exported transaction list may be easier to share, but it is evidence supplied by the user rather than a cryptographic verification path.

Before sharing anything, write down the exact claim the recipient needs to verify: funds arrived, a particular amount was sent, a balance exists at a date, or an account can be reconciled over time. Then use the narrowest supported mechanism. Selective disclosure fails when convenience turns a limited question into open-ended surveillance.

Payment disclosures are a different tool

ZIP 311 describes a mechanism for proving facts about selected shielded spends or outputs inside one transaction. Its use cases include proof of payment, donation matching, merchant disputes, and shielded withdrawals. Unlike handing over a full viewing key, a transaction-specific proof can be designed not to reveal unrelated activity.

However, ZIP 311 is marked Draft and still contains unfinished transparent-input work. It should be treated as a technical specification, not a promise that every Zcash wallet can generate or verify these proofs today. Check the exact wallet and protocol support before building a workflow around it.

How to share viewing access responsibly

Confirm the key type, receiver pool, account scope, scan start height, and software the recipient will use. Send the credential through an authenticated channel and test with an expected transaction before assuming an empty result means no activity. A wallet can miss data if it does not support the key format or has not scanned the right blocks.

Keep a record of who received the key and why. You can stop future access by moving funds to a new account under new viewing authority, but you cannot erase information the recipient already learned. Treat viewing keys as sensitive financial credentials even though they cannot move money.

What selective disclosure does not solve

Disclosure tools do not authenticate every story attached to a transaction. ZIP 310 distinguishes information a full viewing key guarantees from information that remains undefined or merely suggested. For example, protocol data may not prove the human identity behind a diversified address, and a memo is not automatically a signed statement from a sender.

Good verification combines cryptographic evidence with clear business context: who is making the claim, which account is in scope, what period is covered, and what the verifier is expected to conclude.

FAQ