Got different Public keys from same Private key. `eth-crypto`'s `recoverPublicKey()` and MetaMask's `eth_getEncryptionPublicKey`

Question

Update (2022.03.25)

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.

Update (2022.03.15)

Now message encrypting works. But message decrypting still doesn't work with public key from eth_getEncryptionPublicKey + eth_decrypt. I've updated the Gist

---

Preface:

1. I have a project that requires encrypting / decrypting multiple messages.
2. Calling ethereum.request() for encrypting and decrypting triggers many MetaMask pop-ups and requires many user interactions.
3. I found eth-crypto which seems to be able to reduce user interactions by calling it's built-in encrypt/decrypt functions.

What I found:

1. With the same account (private key) in MetaMask, I got different pubkey if retrieving/recovering in different ways.
2. Those pubkeys look different, in different length.
3. Those keys seem not compatible to each other. When using them to encrypt message for example:
   • Works: Use EthCrypto with EthCrypto recovered public key, Use Ethereum (MetaMask) with EthCrypto recovered public key, Use Ethereum with Ethereum public key.
   • Doesn't work: Use EthCrypto with Ethereum (MetaMask) public key. (I want this most.)

Question:

1. Are they totally different things?
2. Is there any way to convert from one to another?
3. What do I need to do to make the pubkey from eth_getEncryptionPublicKey works with EthCrypto.encryptWithPublicKey()?

Sample codes:

Link to gist (my test codes)

1. Method 1: Get pubkey from web3/MetaMask directly

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

bbfbb7e44ad3f14dfdf7089eab8a2a8407efddc5dbfeb3b00e15d2f996d1ab06 (string length 64)

let pubkey_eth_decompressed_prefix02 = EthCrypto.publicKey.decompress("02" + Buffer.from(pubkey_eth, "base64").toString("hex"));
let pubkey_eth_decompressed_prefix03 = EthCrypto.publicKey.decompress("03" + Buffer.from(pubkey_eth, "base64").toString("hex"));
// results are different, both are not usable by encryption function from eth-crypto

window.Ethereum: My public key decompressed (prefix 02) from Ethereum is bbfbb7e44ad3f14dfdf7089eab8a2a8407efddc5dbfeb3b00e15d2f996d1ab069936428a47bcf50da95add19994b7d747b2dc6b3e18fd4034bd551fdd938314c (string length 128)
window.Ethereum: My public key decompressed (prefix 03) from Ethereum is bbfbb7e44ad3f14dfdf7089eab8a2a8407efddc5dbfeb3b00e15d2f996d1ab0666c9bd75b8430af256a522e666b4828b84d2394c1e702bfcb42aae0126c7cae3 (string length 128)

2. Method 2: Recover pubkey from MetaMask signed message, using eth-crypto

let secretMsgSignature = await web3.eth.sign(
    EthCrypto.hash.keccak256("Secret message"),
    selectedAccount
);
const secretMsgSignature_personal = await new Promise((resolve, reject) => {
    web3.currentProvider.sendAsync({
        "method": "personal_sign",
        "params": [web3.utils.utf8ToHex("Secret message"), selectedAccount],
        "from": selectedAccount,
    }, (err, response) => {
        if (err) {return reject(err);}
        resolve(response.result);
    });
});

Signature is 0xdb2fe9c70f4bfdc69299bf0dabe823b7e405dafdaae5ca0ae4eef8ef1b3abd1e5a7b777cb71608bfc80e4d33c3fdf1d6bdbeeac861a14d718e16621263b1b23e1c
Signature (personal) is 0x0a42e36b34adbaa8c7ac926b0fb78d1b91bc1f19ae2cf0cb06a8330958f868130ec68ed47ae25474fe1f1cae202c0fb5e85f4e6baeaf1ac7f609002d81f6fc981b
Both length 132

let pubkey_ethcrypto = EthCrypto.recoverPublicKey(
    secretMsgSignature,
    EthCrypto.hash.keccak256("Secret message")
);
let pubkey_ethcrypto_compressed = EthCrypto.publicKey.compress(pubkey_ethcrypto);

// -------

const pubkey_ethcrypto_personal = EthCrypto.recoverPublicKey(
    secretMsgSignature_personal,
    web3.eth.accounts.hashMessage("Secret message")
);
let pubkey_ethcrypto_compressed_personal = EthCrypto.publicKey.compress(pubkey_ethcrypto_personal);
// none of the two is the same as the pubkey we got directly from metamask

EthCrypto: My public key is f4ce65a8d150c0434e16cf4de4c22fa1870b7eeb963ce9a503c504b21f8fe52f74bd3a005bd3d07eb0ea39e048452178f22cb02214810f538962bef40104ff68 (string length 128)
EthCrypto: My public key compressed is 02f4ce65a8d150c0434e16cf4de4c22fa1870b7eeb963ce9a503c504b21f8fe52f (string length 66)
EthCrypto: My public key (personal) is f4ce65a8d150c0434e16cf4de4c22fa1870b7eeb963ce9a503c504b21f8fe52f74bd3a005bd3d07eb0ea39e048452178f22cb02214810f538962bef40104ff68 (string length 128)
EthCrypto: My public key (personal) compressed is 02f4ce65a8d150c0434e16cf4de4c22fa1870b7eeb963ce9a503c504b21f8fe52f (string length 66)

Answer 1

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.