Add How to Build a Crypto Wallet example (#11)

my-crypto-wallet/01_newAccount.js

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+const {
+  generateMnemonic,
+  mnemonicToEntropy,
+} = require("ethereum-cryptography/bip39");
+const { wordlist } = require("ethereum-cryptography/bip39/wordlists/english");
+const { HDKey } = require("ethereum-cryptography/hdkey");
+const { getPublicKey, ecdsaSign } = require("ethereum-cryptography/secp256k1");
+const { keccak256 } = require("ethereum-cryptography/keccak");
+const { bytesToHex } = require("ethereum-cryptography/utils");
+const { writeFileSync } = require("fs");
+
+function _generateMnemonic() {
+  const strength = 256; // 256 bits, 24 words; default is 128 bits, 12 words
+  const mnemonic = generateMnemonic(wordlist, strength);
+  const entropy = mnemonicToEntropy(mnemonic, wordlist);
+  return { mnemonic, entropy };
+}
+
+function _getHdRootKey(_mnemonic) {
+  return HDKey.fromMasterSeed(_mnemonic);
+}
+
+function _generatePrivateKey(_hdRootKey, _accountIndex) {
+  return _hdRootKey.deriveChild(_accountIndex).privateKey;
+}
+
+function _getPublicKey(_privateKey) {
+  return getPublicKey(_privateKey);
+}
+
+function _getEthAddress(_publicKey) {
+  return keccak256(_publicKey).slice(-20);
+}
+
+function _store(_privateKey, _publicKey, _address) {
+  const accountOne = {
+    privateKey: _privateKey,
+    publicKey: _publicKey,
+    address: _address,
+  };
+  const accountOneData = JSON.stringify(accountOne);
+  writeFileSync("account 2.json", accountOneData);
+}
+
+async function main() {
+  const { mnemonic, entropy } = _generateMnemonic();
+  console.log(`WARNING! Never disclose your Seed Phrase:\n ${mnemonic}`);
+
+  const hdRootKey = _getHdRootKey(entropy);
+
+  const accountOneIndex = 0;
+  const accountOnePrivateKey = _generatePrivateKey(hdRootKey, accountOneIndex);
+
+  const accountOnePublicKey = _getPublicKey(accountOnePrivateKey);
+
+  const accountOneAddress = _getEthAddress(accountOnePublicKey);
+  console.log(`Account One Wallet Address: 0x${bytesToHex(accountOneAddress)}`);
+
+  _store(accountOnePrivateKey, accountOnePublicKey, accountOneAddress);
+}
+
+main()
+  .then(() => process.exit(0))
+  .catch((error) => {
+    console.error(error);
+    process.exit(1);
+  });

my-crypto-wallet/02_restoreWallet.js

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+const { mnemonicToEntropy } = require("ethereum-cryptography/bip39");
+const { wordlist } = require("ethereum-cryptography/bip39/wordlists/english");
+const { HDKey } = require("ethereum-cryptography/hdkey");
+const { getPublicKey } = require("ethereum-cryptography/secp256k1");
+const { keccak256 } = require("ethereum-cryptography/keccak");
+const { bytesToHex } = require("ethereum-cryptography/utils");
+const { writeFileSync } = require("fs");
+
+async function main(_mnemonic) {
+  const entropy = mnemonicToEntropy(_mnemonic, wordlist);
+  const hdRootKey = HDKey.fromMasterSeed(entropy);
+  const privateKey = hdRootKey.deriveChild(0).privateKey;
+  const publicKey = getPublicKey(privateKey);
+  const address = keccak256(publicKey).slice(-20);
+  console.log(`Account One Wallet Address: 0x${bytesToHex(address)}`);
+
+  const accountOne = {
+    privateKey: privateKey,
+    publicKey: publicKey,
+    address: address,
+  };
+  const accountOneData = JSON.stringify(accountOne);
+  writeFileSync("account 1.json", accountOneData);
+}
+
+main(process.argv[2])
+  .then(() => process.exit(0))
+  .catch((error) => {
+    console.error(error);
+    process.exit(1);
+  });

my-crypto-wallet/03_send.js

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+const { getDefaultProvider, Wallet, utils } = require("ethers");
+const { readFileSync } = require("fs");
+
+async function main(_receiverAddress, _ethAmount) {
+  const network = "goerli";
+  const provider = getDefaultProvider(network);
+
+  const accountRawData = readFileSync("account 1.json", "utf8");
+  const accountData = JSON.parse(accountRawData);
+
+  const privateKey = Object.values(accountData.privateKey);
+
+  const signer = new Wallet(privateKey, provider);
+
+  const transaction = await signer.sendTransaction({
+    to: _receiverAddress,
+    value: utils.parseEther(_ethAmount),
+  });
+
+  console.log(transaction);
+}
+
+main(process.argv[2], process.argv[3])
+  .then(() => process.exit(0))
+  .catch((error) => {
+    console.error(error);
+    process.exit(1);
+  });

my-crypto-wallet/package.json

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+{
+  "name": "my-crypto-wallet",
+  "version": "1.0.0",
+  "main": "index.js",
+  "license": "MIT",
+  "dependencies": {
+    "ethereum-cryptography": "^1.0.3",
+    "ethers": "^5.6.8"
+  }
+}