What is ecash in bitcoin, and what are Cashu and Fedimint?

Ecash in bitcoin is a kind of digital cash that represents bitcoin held by a mint. You deposit bitcoin, usually over Lightning, and receive tokens that you can send to others and later redeem. The idea traces back to cryptographer David Chaum, whose blind signature work in the early 1980s made private digital payments possible. Cashu and Fedimint bring that idea to bitcoin.

How does Chaumian ecash work?

The key tool is the blind signature. When you get tokens, your wallet hides the token data before the mint signs it. The mint confirms the value but never sees the final token. When the token is later spent, the mint can verify its own signature and check that it has not been spent before, yet it cannot connect that spend to the original withdrawal. The Cashu site describes this as the mint being unable to link a withdrawal to the later spend. This gives ecash strong payment privacy compared with an account-based custodial wallet.

What is Cashu?

Cashu is a free, open-source protocol for Chaumian ecash on bitcoin. It has no company or token behind it, only a public specification split into documents called NUTs, with code under the MIT license. Anyone can run a mint for their own app, and the mint keeps no database of user accounts. Mints connect to the Lightning Network, issuing tokens when they receive a Lightning payment and paying out over Lightning when tokens are redeemed.

Cashu tokens are bearer tokens. They can be passed around as short text strings in a chat, email or QR code, and payments are instant and final. Tokens can also carry spending conditions such as a public key lock or a hash time lock. Implementations exist in Python, Rust, TypeScript and Kotlin, and some Lightning wallets use Cashu. For example, Zeus offers Cashu-based Lightning addresses.

What is Fedimint in bitcoin?

Fedimint is open-source federated ecash. Instead of one operator, a group of community members called guardians runs the mint together. Each guardian holds one key to a shared multisig bitcoin wallet, so no single guardian can move the funds alone.

Fedimint is built to keep working if some guardians fail or act badly. Its guide says a federation of 4 guardians tolerates 1 faulty or offline guardian, 7 tolerate 2 and 10 tolerate 3. As of November 2026, the maximum is 20 guardians. Users can pay with ecash inside the federation, over Lightning or on-chain.

What does an ecash mint control?

An ecash mint, or federation, holds the actual bitcoin. Cashu's site puts it plainly, ecash is a claim on its mint, not a deposit. If the operator disappears, is hacked or refuses to redeem, the tokens can lose their backing. Fedimint lowers single-operator risk, but only if enough guardians stay honest and online. Ecash also differs from on-chain self-custody, where you hold your own private key. Ecash is best understood as private, community or operator custody, with trade-offs that depend on who runs the mint.