What is view key?

A secret that lets a holder see a wallet's incoming transactions without being able to spend them.

It exists because privacy chains hide by default. On Bitcoin or Ethereum, anyone with your address can read your entire history whether you like it or not. On Monero, nobody can, including you, without the right key. The view key is how selective disclosure is made possible on a chain that otherwise reveals nothing.

The mistake is treating it as a temporary permission. Handing over a view key is not like granting an app access you can revoke. A key that has been seen cannot be un-seen.

How it works

A Monero wallet is built from two key pairs, spend and view. The view key allows its holder to scan the chain and identify outputs belonging to the wallet, decrypting the amounts. The spend key is what authorizes moving them. Separating the two means you can give someone the ability to audit without the ability to steal, as described in the Monero project's documentation.

The private view key is normally derived from the wallet seed, so it is recoverable from a backup and does not need separate storage. Sharing it is a deliberate act: you export the key and hand it to an accountant, an auditor, a tax preparer, or an exchange investigating a deposit.

The limits are worth knowing. A view key reveals incoming transactions well and outgoing transactions incompletely, since spends are constructed with the spend key and are not fully reconstructible from viewing alone. Different privacy chains implement this differently, and Zcash uses a comparable viewing key for shielded addresses.

It is also the mechanism behind proof of reserves on privacy chains, where an exchange publishes a view key so anyone can verify its holdings without the ability to move them.

Example

Illustrative. Your accountant needs a year of Monero receipts for a tax return. You export the private view key and the wallet address and send both.

They import them into a watch-only wallet, scan the chain, and see every payment the wallet received with dates and amounts. They cannot construct a transaction, because that requires the spend key you did not send. The exposure is that they now see every incoming payment the wallet has ever received, before and after the year in question, permanently, and so does anyone who later reads that email.

Why it matters when you buy

Privacy coins are unevenly available. Several exchanges have delisted them in response to regulatory pressure, and where they are listed, deposits are sometimes reviewed more closely, which is when a view key gets requested. The coin pages show which venues list each asset and where, and the jurisdiction pages cover local restrictions.

Related terms

• privacy coin: the assets this applies to
• stealth address: why recipients are hidden by default
• shielded transaction: the equivalent on Zcash
• watch only wallet: what a view key creates
• proof of reserves: an audit use of view keys
• xpub: the transparent-chain counterpart

Questions

Can someone steal my coins with a view key?

No. Spending requires the spend key, which the view key does not contain and cannot derive. The risk from sharing is disclosure rather than theft.

Can I revoke a view key I shared?

Not really. The only way to stop someone seeing new activity is to move funds to a new wallet with new keys, and everything they already saw remains visible to them.

Does a view key show outgoing payments?

Incompletely. It identifies incoming outputs reliably, and reconstructing spends requires information the view key alone does not provide. For proving a specific payment, a transaction proof for that transfer is the narrower tool.