Go - Generate an SSH Public Key

Question

I'm trying to generate a keypair to be used for SSH in Go. I seem to be creating a private key just fine, although I can't figure out how to generate a public key in the correct format.

Here's the code:

privateKey, err := rsa.GenerateKey(rand.Reader, 2014)
if err != nil {
    return nil, err
}

privateKeyDer := x509.MarshalPKCS1PrivateKey(privateKey)
privateKeyBlock := pem.Block{
    Type:    "RSA PRIVATE KEY",
    Headers: nil,
    Bytes:   privateKeyDer,
}
privateKeyPem := string(pem.EncodeToMemory(&privateKeyBlock))

publicKey := privateKey.PublicKey
publicKeyDer, err := x509.MarshalPKIXPublicKey(&publicKey)
if err != nil {
    return nil, err
}

publicKeyBlock := pem.Block{
    Type:    "PUBLIC KEY",
    Headers: nil,
    Bytes:   publicKeyDer,
}
publicKeyPem := string(pem.EncodeToMemory(&publicKeyBlock))

    fmt.Println(privateKeyPem)
    fmt.Println(publicKeyPem)

I get this output:

-----BEGIN RSA PRIVATE KEY-----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-----END RSA PRIVATE KEY-----
 -----BEGIN PUBLIC KEY-----
MIIBHDANBgkqhkiG9w0BAQEFAAOCAQkAMIIBBAKB/DFnL5O2LCGJQJ/6W299AsrX
sHU3nsGVTbjoDqXjdHboSqAuv0apoyTPQuBVNff1X0AdVDwjat2vSAukST/3PmRX
4TNU4jV0rog/z6grexOCSl3oatJOi80t+F6uuTD6XTh5C5yDQNI/sTyaPpydbI+P
87UuY4UapZaei7fwc3MfurJ+jwEJc+jOWbll2YhIgCOuIe0GRX4e4CDC2KiO/BqA
WCPQNjk0Y0iC2+J+2Qy3QBOJTVO8E2DzIhIe4VjKK6OVVesYmJWSXX/Jx382CvUD
v5ss8mxGEs3yge4zeQ0GPPDaqTFwOJ1uppsdj10ZiW92E8v/fYwlBNGfrQIDAQAB
-----END PUBLIC KEY-----

Answer 1

If you're looking for generating keys in the format that will be included in an OpenSSH authorized_key file, below is a helper I wrote recently:

// MakeSSHKeyPair make a pair of public and private keys for SSH access.
// Public key is encoded in the format for inclusion in an OpenSSH authorized_keys file.
// Private Key generated is PEM encoded
func MakeSSHKeyPair(pubKeyPath, privateKeyPath string) error {
    privateKey, err := rsa.GenerateKey(rand.Reader, 1024)
    if err != nil {
        return err
    }

    // generate and write private key as PEM
    privateKeyFile, err := os.Create(privateKeyPath)
    defer privateKeyFile.Close()
    if err != nil {
        return err
    }
    privateKeyPEM := &pem.Block{Type: "RSA PRIVATE KEY", Bytes: x509.MarshalPKCS1PrivateKey(privateKey)}
    if err := pem.Encode(privateKeyFile, privateKeyPEM); err != nil {
        return err
    }

    // generate and write public key
    pub, err := ssh.NewPublicKey(&privateKey.PublicKey)
    if err != nil {
        return err
    }
    return ioutil.WriteFile(pubKeyPath, ssh.MarshalAuthorizedKey(pub), 0655)
}

Answer 2

You can use the OpenSSH ssh-keygen to convert the file.

Write the PEM out to a file (e.g. pubkey.pem) and convert it like so:

ssh-keygen -m PKCS8 -f pubkey.pem -i

Or you can use the MarshalAuthorizedKey function from the ssh package:

// using publicKey from above.
// though NewPublicKey takes an interface{}, it must be a pointer to a key.
pub, err := ssh.NewPublicKey(&publicKey)
if err != nil {
    // do something
}
pubBytes := ssh.MarshalAuthorizedKey(pub)
fmt.Println(string(pubBytes))