view key
A view key is a special key that grants read-only access to your otherwise-private transactions: it lets a holder see what came in (and sometimes what went out) without granting any power to spend. It is the cryptographic answer to a real tension in private money — you may genuinely want privacy from the public yet need to selectively reveal your activity to an auditor, an accountant, a tax authority, or an exchange's compliance desk. The view key lets you open a window into your finances for exactly one party, while everyone else still sees nothing.
The design rests on separating the keys that detect transactions from the keys that authorise them. In Monero, a wallet has a spend keypair and a view keypair; the private view key lets you (or anyone you share it with) scan the blockchain and recognise which stealth-address outputs were sent to you, by recomputing the Diffie-Hellman shared secret, but it cannot produce the key images and signatures needed to spend. In Zcash Sapling and later, the hierarchy is richer: an incoming viewing key (IVK) decrypts the notes you received, while a full viewing key (FVK) reveals both incoming and outgoing notes for complete auditability — yet neither confers spend authority, which stays with the separate spending key.
This makes selective disclosure practical. You can prove to a regulator that your shielded transactions are clean, or let an accountant reconcile your books, by sharing a view key scoped to exactly what they need, without ever risking your funds. Some proposals extend this idea to viewing keys that can be revealed per-transaction or delegated for a time window, giving fine-grained, auditable transparency on demand inside an otherwise private system.
Two honest caveats. First, a view key is a blunt instrument over time: sharing it typically reveals all matching transactions, past and future, not just the ones you intended, so once disclosed it is hard to walk back. Second, the exact visibility differs by protocol — a Monero private view key alone reliably reveals incoming payments but historically could not by itself fully determine which of your outputs you had already spent, so 'view' does not always mean a complete ledger. Treat a view key as a powerful but coarse audit grant, and scope it deliberately.
A business runs a Monero donation address and must report income for tax. It hands its private view key (not the spend key) to its accountant, who scans the chain, recognises every incoming donation output, and totals the revenue — all without any ability to move a single coin from the wallet.
Sharing only the view key enables auditing while spending stays impossible.
A view key separates seeing from spending, but it cannot un-share: there is no built-in revocation. Disclosing your view key is closer to publishing a permanent read-only statement than to granting a session that you can later cut off.