Saving Privatekey (PKCS8) & Publickey (X509) into PEM Files and reading them in Java

Question

I am generating a key pair in Koltin and saving them into two files, when trying to read these files in any other language than go, it causes and error "Invalid key format".

Here the go Code which generates the keys, encodes them and saves them into pem files. The privatekey should be PKCS8 encoded and the publickey X509 encoded.

func ExportPublicKeyAsPemStr(pubkey *rsa.PublicKey) string {
    pubkeyPem := string(pem.EncodeToMemory(&pem.Block{Type: "RSA PUBLIC KEY",Bytes: x509.MarshalPKCS1PublicKey(pubkey)}))
    err := createFile("C:/tmp/publickey.pub", pubkeyPem)
    if err != nil {
        panic(err)
    }
    return pubkeyPem
}
func ExportPrivateKeyAsPemStr(privatekey *rsa.PrivateKey) string {
    privatekeyBytes, err := x509.MarshalPKCS8PrivateKey(privatekey)
    if err != nil {
        panic(err)
    }
    privatekeyPem := string(pem.EncodeToMemory(&pem.Block{Type: "RSA PRIVATE KEY",Bytes: privatekeyBytes}))
    err = createFile("C:/tmp/privatekey.key", privatekeyPem)
    if err != nil {
        panic(err)
    }
    return privatekeyPem
}
func ExportMsgAsPemStr(msg []byte) string {
    msgPem := string(pem.EncodeToMemory(&pem.Block{Type: "MESSAGE",Bytes: msg}))
    err := createFile("C:/tmp/message.pem", msgPem)
    if err != nil {
        panic(err)
    }
    return msgPem
}
func main() {
    bits := 2048
    flag.Parse()
    //args := flag.Args()
    //m:=args[0]
    bobPrivateKey, _ := rsa.GenerateKey(rand.Reader,bits)

    bobPublicKey := &bobPrivateKey.PublicKey
    fmt.Printf("%s\n",  ExportPrivateKeyAsPemStr(bobPrivateKey))
    fmt.Printf("%s\n", ExportPublicKeyAsPemStr(bobPublicKey))
    message := []byte("This is a message with confidential text")
    label := []byte("")
    hash := sha256.New()
    ciphertext, _ := rsa.EncryptOAEP(hash, rand.Reader, bobPublicKey, message,label)
    fmt.Printf("%s\n",ExportMsgAsPemStr(ciphertext))
    plainText, _:= rsa.DecryptOAEP(hash, rand.Reader, bobPrivateKey, ciphertext, label)
    fmt.Printf("RSA decrypted to [%s]", plainText)
}

func createFile(name string, data string) error {
    f, err := os.Create(name)
    if err != nil {
        return err
    }
    defer f.Close()
    _, err = f.WriteString(data)
    if err != nil {
        return err
    }
    return nil
}

Here some sample content of the two pem files: Privatekey:

Publickey:

Now if I for example enter them into this website or this one(Algorithm RS256) I get an InvalidKeyException...

Could someone tell what I am doing wrong?

Your private key seems to be a Pkcs8-key, but it has the wrong start- and end-line which should be `-----BEGIN PRIVATE KEY-----` and `-----END PRIVATE KEY-----`. Your public key seems to be a public Pkcs1-key, but not an X.509-key. I suspect that the `MarshalPKIXPublicKey`-method must be used to generate an X.509-key whose start- and end-line is `-----BEGIN PUBLIC KEY-----` and `-----END PUBLIC KEY-----`. For an overview of the different formats see [here](https://stackoverflow.com/a/49878687/9014097) and [here](https://tls.mbed.org/kb/cryptography/asn1-key-structures-in-der-and-pem). — Topaco, Oct 16 '19 at 09:08
The PEM header and footer are indeed correct the way you do it. Also what you suspected proved to be right. Thx a lot — mait.taim, Oct 16 '19 at 10:02

Saving Privatekey (PKCS8) & Publickey (X509) into PEM Files and reading them in Java

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