Cashu and nutzaps in plain words

You may have seen "nutzap" or "ecash" in a Nostr client and wondered how it differs from a normal zap. Short version: a normal zap is a Lightning payment; a nutzap is a Cashu ecash token sent over Nostr. Here's what that means for you.

What Cashu is#

Cashu is "Chaumian ecash" for bitcoin. A mint holds real bitcoin (received over Lightning) and hands out signed tokens worth the same number of sats. You can pass those tokens to anyone, and later redeem them at the mint for Lightning sats again.

The mint signs tokens blindly, so it can't link who received a token to who spends it. That's the privacy win.

The catch: the mint holds the money#

Cashu is custodial. The tokens are only worth something as long as the mint honors them. A mint can go offline, run away, or be hacked.

So:

• Only hold small amounts in ecash, like spending money in a pocket.
• Spread across mints you have reason to trust (run by someone known, been around a while).
• Move larger balances out to a Lightning wallet you control, or on-chain.

What a nutzap is#

With a normal zap (NIP-57), the recipient needs a Lightning address, and the payment goes through their wallet provider's server, which also has to publish a zap receipt.

With a nutzap (NIP-61):

1. The recipient publishes a small Nostr event saying "these are the mints I accept, and here is a public key to lock tokens to."
2. You mint (or already hold) a token at one of those mints, lock it to their key, and publish it as a Nostr event.
3. Only they can spend it. Their wallet picks it up next time they open the client and swaps it at the mint.

No Lightning address, no always-online server needed on their side. That's why it suits people who don't run a node or don't want a custodial Lightning address.

Where the wallet lives (NIP-60)#

Many nutzap-capable clients keep your ecash wallet on Nostr relays, encrypted to your own key (NIP-60). Log in with the same key in another client that supports it and your balance follows you.

That also means: if your nsec leaks, your ecash leaks with it. Treat the wallet like your key. Another reason to keep the balance small.

Common problems#

• "I nutzapped and they never got it." They may not have a nutzap setup (no mint list event), or your mint isn't on their list. Clients should only offer nutzaps when the recipient advertises support.
• "My balance shows zero in another client." That client may not support NIP-60, or isn't reading the relays where your wallet events live.
• "The mint is down." Your tokens are stuck until it comes back. Nothing you can do client-side; this is the custodial trade-off.

Should you use it?#

For tipping a few hundred sats, yes, it's handy and private. For savings, no. Think "cash in a pocket", not "bank".

Questions? Reply and I'll add them here.