ecash-lib

Library for eCash transaction building.

• Compatible: Works on the browser using webpack, on NodeJS, jest etc.
• Fast: Accelerated using the highly optimized secp256k1 library compiled to WebAssembly
• Simple to use: Describe the tx to build in one TxBuilder object, and build the tx with just one sign call
• SLP/ALP enabled: Functions to build the SLP/ALP eMPP scripts
• Flexible: The "Signatory" mechanism can accommodate anything from simple wallet transfers to complex Script covenants, e.g. eCash Agora
• Schnorr: eCash lib supports Schnorr and ECDSA signatures
• Precise leftover ("change") computation: The tx size estimator will be exact for Schnorr signatures and very close for ECDSA signatures, even for complex scripts

Usage

This library works for both browser and NodeJS.

Installation

npm install --save ecash-lib

Setup

To use this library, you first have to initialize the WebAssembly module:

import { initWasm } from 'ecash-lib';
await initWasm();

After that, to sign signatures, you need an "Ecc" instance:

import { Ecc } from 'ecash-lib';
const ecc = new Ecc();

Note: You should only call this function once, as it's fairly expensive to setup, it internally precomputes some elliptic curve field elements, which takes some time

Usage

Now you're ready to sign your first transactions:

import {
    Ecc,
    P2PKHSignatory,
    Script,
    TxBuilder,
    fromHex,
    initWasm,
    shaRmd160,
    toHex,
    ALL_BIP143,
} from 'ecash-lib';

// Download and compile WebAssembly
await initWasm();
// Build a signature context for elliptic curve cryptography (ECC)
const ecc = new Ecc();
const walletSk = fromHex(
    'e6ae1669c47d092eff3eb652bea535331c338e29f34be709bc4055655cd0e950',
);
const walletPk = ecc.derivePubkey(walletSk);
const walletPkh = shaRmd160(walletPk);
const walletP2pkh = Script.p2pkh(walletPkh);
// TxId with unspent funds for the above wallet
const walletUtxo = {
    txid: '0000000000000000000000000000000000000000000000000000000000000000',
    outIdx: 0,
};
// Tx builder
const txBuild = new TxBuilder({
    inputs: [
        {
            input: {
                prevOut: walletUtxo,
                signData: {
                    value: 1000,
                    outputScript: walletP2pkh,
                },
            },
            signatory: P2PKHSignatory(walletSk, walletPk, ALL_BIP143),
        },
    ],
    outputs: [
        {
            value: 0,
            script: new Script(fromHex('6a68656c6c6f')),
        },
        walletP2pkh,
    ],
});
const tx = txBuild.sign(ecc, 1000, 546);
const rawTx = tx.ser();
console.log(toHex(rawTx));

Changelog

• 0.1.1 - Validation that feePerKb is an integer
• 0.1.2 - Upgrade dependencies D16373
• 0.1.3 - Export slpAmount function D16379
• 0.2.0 - Add Script.fromAddress method to convert cashaddr addresses to Script
• 0.2.1 - Fix fee estimation for signatories that depend on tx outputs D16673
• 1.0.0 - (Breaking change) Modify GenesisInfo so that auth and data types match D17194
• 1.0.1 - Include ecashaddrjs and chronik-client installations from npmjs instead of local, to prevent need for peer dependencies D17215
• 1.1.0 - Add support for the original pre-UAHF Bitcoin signatures, so we can sign transactions for other blockchains like BTC/DOGE/... D17255
• 1.2.0 - Add Address class for cashaddr and legacy addresses. D17269