eth-crypto and web3, public key retrieving, sign, recover and encrypting test

eth-pubkey-tests.js

/* eslint-disable no-console */
const EthCrypto = require("eth-crypto");
const sigUtil = require("@metamask/eth-sig-util");
const ethUtil = require("ethereumjs-util");

async function test (provider, selectedAccount) {
	// eslint-disable-next-line no-undef
	const web3 = new Web3(provider);
	//   const accounts = await web3.eth.getAccounts();
	//   selectedAccount = accounts[0];

	console.log("Wallet is", web3.eth.accounts.wallet);

	//
	// Get signature
	//
	console.warn("Get signature\n================");

	// Deprecated: This works must shows warning.
	// https://ethereum.stackexchange.com/questions/41993/how-to-encrypt-a-message-using-only-the-public-key-from-web3-eth-sign/63983#63983
	// let secretMsgSignature = await web3.eth.sign(
	// 	web3.eth.accounts.hashMessage("Secret message"),
	// 	selectedAccount
	// );
	// console.log("Signature is", secretMsgSignature);

	const secretMsgSignature = await new Promise((resolve, reject) => {
		window.ethereum.sendAsync({
			"method": "personal_sign",
			"params": [web3.utils.utf8ToHex("Secret message"), selectedAccount],
			"from": selectedAccount,
		}, (err, response) => {
			if (err) {return reject(err);}
			resolve(response.result);
		});
	});
	console.log("Signature is", secretMsgSignature);

	//
	// Get signers address from signatures
	//
	console.warn("Get signers address from signatures\n================");

	let signerAddress = EthCrypto.recover(
		secretMsgSignature,
		web3.eth.accounts.hashMessage("Secret message")
	);
	console.log("Signer address is", signerAddress);

	//
	// Get public key
	//
	console.warn("Get public key\n================");

	const pubkey_ethcrypto = EthCrypto.recoverPublicKey(
		secretMsgSignature,
		web3.eth.accounts.hashMessage("Secret message")
	);
	console.log("EthCrypto: My public key is", pubkey_ethcrypto);
	let pubkey_ethcrypto_compressed = EthCrypto.publicKey.compress(pubkey_ethcrypto);
	console.log("EthCrypto: My public key compressed is", pubkey_ethcrypto_compressed);
	console.log("EthCrypto: My public key compressed length is", pubkey_ethcrypto_compressed.length);

	//
	// Get Public Key from Ethereum (MetaMask)
	//
	console.warn("Get Public Key from Ethereum (MetaMask)\n================");

	let pubkey_eth = await window.ethereum.request({
		"method": "eth_getEncryptionPublicKey",
		"params": [selectedAccount], // you must have access to the specified account
	});
	console.log("window.Ethereum: My public Key from Ethereum (MetaMask):", pubkey_eth);
	console.log("window.Ethereum: My public key from Ethereum (MetaMask) is", Buffer.from(pubkey_eth, "base64").toString("hex"));
	console.log("window.Ethereum: My public key from Ethereum (MetaMask) length is", Buffer.from(pubkey_eth, "base64").toString("hex").length);

	let pubkey_eth_decompressed_prefix02 = EthCrypto.publicKey.decompress("02" + Buffer.from(pubkey_eth, "base64").toString("hex"));
	console.log("window.Ethereum: My public key decompressed (prefix 02) from Ethereum (MetaMask) is", pubkey_eth_decompressed_prefix02);
	console.log("window.Ethereum: My public key decompressed (prefix 02) length from Ethereum (MetaMask) is", pubkey_eth_decompressed_prefix02.length);
	let pubkey_eth_decompressed_prefix03 = EthCrypto.publicKey.decompress("03" + Buffer.from(pubkey_eth, "base64").toString("hex"));
	console.log("window.Ethereum: My public key decompressed (prefix 03) from Ethereum (MetaMask) is", pubkey_eth_decompressed_prefix03);
	console.log("window.Ethereum: My public key decompressed (prefix 03) length from Ethereum (MetaMask) is", pubkey_eth_decompressed_prefix03.length);


	//
	// Encrypt message
	//
	console.warn("Encrypt message\n================");

	// Encrypt message: Use EthCrypto with EthCrypto public key
	console.info("Encrypt message: Use EthCrypto with EthCrypto public key");

	const encmsg_ethcrypto_ethcryptokey_raw = await EthCrypto.encryptWithPublicKey(
		pubkey_ethcrypto,
		"Secret message"
	);
	const encmsg_ethcrypto_ethcryptokey = ethUtil.bufferToHex(
		Buffer.from(
			JSON.stringify(
				encmsg_ethcrypto_ethcryptokey_raw
			),
			"utf8"
		)
	);
	console.log("EthCrypto: Raw encrypted message (ethcrypto key) is", encmsg_ethcrypto_ethcryptokey_raw);
	console.log("EthCrypto: Message encrypted (ethcrypto key) is", encmsg_ethcrypto_ethcryptokey);
	console.log("EthCrypto: Message encrypted (ethcrypto key) EthCrypto.cipher.stringify is", EthCrypto.cipher.stringify(encmsg_ethcrypto_ethcryptokey_raw));

	// Encrypt message: Use EthCrypto with Ethereum (MetaMask) public key
	console.info("Encrypt message: Use EthCrypto with Ethereum (MetaMask) public key");

	const encmsg_ethcrypto_ethkey_prefix02_raw = await EthCrypto.encryptWithPublicKey(
		pubkey_eth_decompressed_prefix02, // pubkey_eth is the public key of the Ethereum (MetaMask) account
		"Secret message"
	);
	const encmsg_ethcrypto_ethkey_prefix02 = ethUtil.bufferToHex(
		Buffer.from(JSON.stringify(encmsg_ethcrypto_ethkey_prefix02_raw), "utf8")
	);
	console.log(
		"EthCrypto: Raw encrypted message (eth key prefix 02) is",
		encmsg_ethcrypto_ethkey_prefix02_raw
	);
	console.log("EthCrypto: Message encrypted (eth key prefix 02) is", encmsg_ethcrypto_ethkey_prefix02);

	const encmsg_ethcrypto_ethkey_prefix03_raw = await EthCrypto.encryptWithPublicKey(
		pubkey_eth_decompressed_prefix03, // pubkey_eth is the public key of the Ethereum (MetaMask) account
		"Secret message"
	);
	const encmsg_ethcrypto_ethkey_prefix03 = ethUtil.bufferToHex(
		Buffer.from(JSON.stringify(encmsg_ethcrypto_ethkey_prefix03_raw), "utf8")
	);
	console.log(
		"EthCrypto: Raw encrypted message (eth key prefix 03) is",
		encmsg_ethcrypto_ethkey_prefix03_raw
	);
	console.log("EthCrypto: Message encrypted (eth key prefix 03) is", encmsg_ethcrypto_ethkey_prefix03);

	// Encrypt message: Use Ethereum with EthCrypto public key
	console.info("Encrypt message: Use Ethereum with EthCrypto public key");

	const encmsg_eth_ethcryptokey_raw = sigUtil.encrypt({
		"publicKey": Buffer.from(pubkey_ethcrypto_compressed.substring(2), "hex").toString(
			"base64"
		),
		"data": "Secret message",
		"version": "x25519-xsalsa20-poly1305",
	});
	const encmsg_eth_ethcryptokey = ethUtil.bufferToHex(
		Buffer.from(JSON.stringify(encmsg_eth_ethcryptokey_raw), "utf8")
	);
	console.log("sigUtil: Raw encrypted message (ethcrypto key) is", encmsg_eth_ethcryptokey_raw);
	console.log("sigUtil: Message encrypted (ethcrypto key) is: ", encmsg_eth_ethcryptokey);

	// Encrypt message: Use Ethereum with Ethereum (MetaMask) public key
	console.info("Encrypt message: Use Ethereum with Ethereum (MetaMask) public key");

	const encmsg_eth_ethkey_raw = sigUtil.encrypt({
		"publicKey": pubkey_eth,
		"data": "Secret message",
		"version": "x25519-xsalsa20-poly1305",
	});
	const encmsg_eth_ethkey = ethUtil.bufferToHex(
		Buffer.from(
			JSON.stringify(
				encmsg_eth_ethkey_raw
			),
			"utf8"
		)
	);
	console.log("sigUtil: Raw encrypted message (eth key) is", encmsg_eth_ethkey_raw);
	console.log("sigUtil: Message encrypted (eth key) is: ", encmsg_eth_ethkey);


	//
	// Decrypt message
	//
	console.warn("Decrypt messages\n================");

	// Decrypt message: Use Ethereum with Ethereum public key
	// console.info("Decrypt message: Use Ethereum with Ethereum public key");
	// const decmsg_eth_byEth = await window.ethereum.request({
	// 	"method": "eth_decrypt",
	// 	"params": [encmsg_eth_ethkey, selectedAccount], // you must have access to the specified account
	// });
	// console.log("window.Ethereum: Decrypted message from Ethereum is: ", decmsg_eth_byEth);
}

From @Ismael's comment and MetaMask github issue:

1. The key from MetaMask's eth_getEncryptionPublicKey rpc is NOT the Public Key of my account, but a different key calculated from my private key with the nacl implementation of the X25519_XSalsa20_Poly1305 algorithm, which is different from Ethereum's default algorithm.
2. MetaMask holds the private key, but it doesn't provide a function to decrypt messages with the private key.