return nil
		}
	}

	pemBlockForKey := func(priv interface{}) *pem.Block {
		switch k := priv.(type) {
		case *rsa.PrivateKey:
			return &pem.Block{Type: "RSA PRIVATE KEY", Bytes: x509.MarshalPKCS1PrivateKey(k)}
		case *ecdsa.PrivateKey:
			b, err := x509.MarshalECPrivateKey(k)
			if err != nil {
				fmt.Fprintf(os.Stderr, "Unable to marshal ECDSA private key: %v", err)
				os.Exit(2)
			}