How to generate, save, importing a keypair into phantom with solana/web3.js v2?

Question

Steven and John answered on how to generate and save a keypair using web3.js v2.
-> see also: How to generate and save a keypair with solana/web3.js v2?

I formatted the private key into base58 (server-side) for importing into Phantom wallet, see below.
However, importing the output, 'GxF5ePs9h98vsW5EpTy8Jf8Fgtg9s1BiAUH1jboXX4td', into Phantom gives an error "incorrect format". Any idea why and how to resolve?

export const generateKeypair = async (): Promise<{ publicKey: string; privateKey: string }> => {
    // Generate a new Ed25519 keypair
    const keypair = await crypto.subtle.generateKey(
        "Ed25519",
        true,
        ["sign", "verify"]
    );

    const publicKey = await getAddressFromPublicKey(keypair.publicKey)

    // Export the private key in JWK format
    const privateKeyJwk = await crypto.subtle.exportKey("jwk", keypair.privateKey);
    console.log(privateKeyJwk)

    // Get the 'd' (private key) from the JWK
    const privateKeyBase64Url = privateKeyJwk.d; ;
    if (!privateKeyBase64Url) throw new Error("Failed to get private key bytes");

    // Decode Base64 to raw bytes (Uint8Array)
    const privateKeyBase64 = privateKeyBase64Url.replace(/-/g, '+').replace(/_/g, '/');  
    const privateKeyBytes = new Uint8Array(atob(privateKeyBase64).split('').map(c => c.charCodeAt(0)));
    console.log(privateKeyBytes)

    // Encode the raw bytes in Base58
    const privateKey = bs58.encode(privateKeyBytes);

    console.log({ publicKey, privateKey })
    return { publicKey, privateKey };
};


// OUTPUT
//   {
//     key_ops: [ 'sign' ],
//     ext: true,
//     crv: 'Ed25519',
//     d: '7QYrNgpIfW5cEXQXE2jjGm-_kIwR40nfi2pVA49dn-4',
//     x: 'Vnxjs2cyrXY9lTYkpqgZh8M5TkUzjbiX4UISNGrnHec',
//     kty: 'OKP'
//   }
//   Uint8Array(32) [
//     237,   6,  43,  54,  10,  72, 125, 110,
//      92,  17, 116,  23,  19, 104, 227,  26,
//     111, 191, 144, 140,  17, 227,  73, 223,
//     139, 106,  85,   3, 143,  93, 159, 238
//   ]
//   {
//     publicKey: '6pc5DUQBRmsegskr7DEZfs3wcLAaSPCwaKkXyEhkRZjt',
//     privateKey: 'GxF5ePs9h98vsW5EpTy8Jf8Fgtg9s1BiAUH1jboXX4td'
//   }

Answer 1

This Phantom help article gives you an indication of what format they expect the key to be in: (link)

Solana private key👇 2P3qgS5A18gGmZJmYHNxYrDYPyfm6S3dJgs8tPW6ki6i2o4y9293r5N8CF7JpEtQiW8mx1kSktpgyDG1xuWNzfsM

That is 64 bytes of data, encoded as a base58 string. This is a typical format for secret keys, consisting of the 32 bytes of the private key, followed by the 32 bytes of its corresponding public key.

Start with your keypair

const keypair = await crypto.subtle.generateKey(
    'Ed25519',
    true, /* extractable */
    ["sign", "verify"]
);

Export the public key bytes

const publicKeyBytes = crypto.subtle.exportKey('raw', keypair.publicKey);

Export the private key bytes

const privateKeyBytes = (await crypto.subtle.exportKey(
  "pkcs8",
  keypair.privateKey
)).slice(-32);

Glue them together and encode as a base58 string

const secretKeyBytes = new Uint8Array([
  ...new Uint8Array(privateKeyBytes),
  ...new Uint8Array(publicKeyBytes),
]);
const encodedSecretKey = getBase58Decoder().decode(secretKeyBytes);