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Cashu

Ecash protocol for Bitcoin. Private, instant, and offline-capable digital cash.

Overview​

Cashu is a free and open-source Chaumian ecash protocol built on Bitcoin. It enables private, instant transactions using blinded tokens that can be sent without revealing sender identity to the mint.

How It Works​

┌─────────────────────────────────────────────────────────┐
│                    Cashu Flow                            │
├─────────────────────────────────────────────────────────┤
│                                                          │
│  1. Deposit                                             │
│     User pays Lightning invoice → Receives tokens       │
│                                                          │
│  2. Send                                                │
│     User A sends tokens to User B (just a string!)     │
│     Mint doesn't know who sent to whom                 │
│                                                          │
│  3. Receive                                             │
│     User B redeems tokens at mint                       │
│     Gets new tokens (breaks linkability)               │
│                                                          │
│  4. Withdraw                                            │
│     User requests Lightning payout                      │
│     Mint pays invoice, burns tokens                     │
│                                                          │
└─────────────────────────────────────────────────────────┘

Key Features​

Privacy​

Traditional:
Alice ──► Bank ──► Bob
Bank sees: Alice sent $10 to Bob

Cashu:
Alice ──► Mint ──► Bob
Mint sees: Someone deposited, someone withdrew
Cannot link: Alice to Bob

Blinded signatures ensure the mint cannot track token flow.

Instant & Offline​

FeatureDescription
InstantNo blockchain confirmation
OfflineSend tokens without internet
FreeNo transaction fees

Tokens are just strings — send via text, QR, Nostr DM.

Token Format​

cashuAeyJ0b2tlbiI6W3sicHJvb2ZzIjpbeyJpZCI6IjAwY...

A Cashu token is a base64-encoded string containing:

  • Mint URL
  • Proofs (blinded signatures)
  • Amount

Protocol​

Nut Specifications​

Cashu is defined by NUTs (Notation, Usage, and Terminology):

NUTFeature
NUT-00Token format
NUT-01Mint public keys
NUT-02Keysets
NUT-03Swap tokens
NUT-04Mint tokens
NUT-05Melt tokens
NUT-06Mint info
NUT-07Token state
NUT-08Lightning payments

API Endpoints​

POST /v1/mint/quote/bolt11    # Get minting quote
POST /v1/mint/bolt11          # Mint tokens
POST /v1/swap                 # Swap tokens
POST /v1/melt/quote/bolt11    # Get melting quote
POST /v1/melt/bolt11          # Melt (withdraw)
GET  /v1/keys                 # Mint public keys
GET  /v1/info                 # Mint information

Using Cashu​

Wallets​

WalletPlatform
NutstashWeb
eNutsMobile
MinibitsMobile
Cashu.meWeb
NutshellCLI

Nostr Integration​

Cashu works great with Nostr:

  • Send tokens via DMs (NIP-04)
  • Zap alternatives
  • Shopstr payments
  • Ecash tips

For Developers​

JavaScript​

import { CashuMint, CashuWallet } from '@cashu/cashu-ts';

// Connect to mint
const mint = new CashuMint('https://mint.example.com');
const wallet = new CashuWallet(mint);

// Get minting quote
const quote = await wallet.getMintQuote(1000);

// After paying Lightning invoice...
const tokens = await wallet.mintTokens(1000, quote.quote);

// Send tokens (just a string)
const tokenString = wallet.getEncodedToken(tokens);

// Receive tokens
const received = await wallet.receive(tokenString);

Running a Mint​

# Using Nutshell
git clone https://github.com/cashubtc/nutshell.git
cd nutshell

# Configure
cp .env.example .env
# Edit .env with your LN node details

# Run
docker-compose up

Mint Backends​

BackendDescription
LNDLightning Network Daemon
CLNCore Lightning
LNbitsAccount system

Trust Model​

┌─────────────────────────────────────────────────────────┐
│                   Trust Model                            │
├─────────────────────────────────────────────────────────┤
│                                                          │
│  What mint CAN do:                                      │
│  ├── Refuse to honor tokens (rug pull)                 │
│  └── Inflate supply (print fake tokens)                │
│                                                          │
│  What mint CANNOT do:                                   │
│  ├── See who sent to whom                              │
│  ├── Link deposits to withdrawals                      │
│  └── Censor specific users                             │
│                                                          │
│  Mitigations:                                           │
│  ├── Use reputable mints                               │
│  ├── Don't hold large balances                         │
│  └── Use multiple mints                                │
│                                                          │
└─────────────────────────────────────────────────────────┘

Comparison​

FeatureCashuLightningOn-chain
PrivacyHighMediumLow
SpeedInstantInstant~10min
OfflineYesNoNo
TrustMintRoutingMiners
FeesNoneSmallVariable

Use Cases​

Private Payments​

Send money without revealing your identity.

Nostr Tipping​

Tip content creators privately via DMs.

Marketplaces​

Shopstr uses Cashu for private commerce.

Gift Cards​

Send digital cash to anyone with a link.

See Also​