export private key in .der file as PKCS#1

Question

I'm writing a java code to generate keys and save them in files, I am using BouncyCastle library to write the privatekey into .pem file using pemwriter(if it is in PKCS#1) and using a regular FileOutputStream to export it into PKCS#8.

Now when exporting into DER, the problem come when trying to export it in PKCS#1.

I searched a lot but cannot find a suitable way to encode the privatekey in PKCS#1 or to convert the regular encoding of java privatekey's (PKCS#8) to PKCS#1, or if you can guide me to convert PrivateKey to RSAPrivateKey or DSAPrivateKey or ECPrivateKey. Here is a snippet of my code to export

        JcePEMEncryptorBuilder builder = new JcePEMEncryptorBuilder("DES-EDE3-CBC");
        PEMEncryptor enc = builder.build(password);

        FileOutputStream fis = new FileOutputStream(new File(privatekey.der));
        if (isPKCS8) {
            if (!encrypt) {
                fis.write(privateKeyBytes);
            } else {
                fis.write(enc.encrypt(privateKeyBytes));
            }
       fis.flush();
       fis.close(); 

where privateKeyBytes are the returned bytes of PrivateKey.getEncoded(). they are in PKCS#8 and if I can convert PrivateKey to RSAPrivateKey or DSAPrivateKey they represent the private key in PKCS#1 format

Answer 1

Apparently you can use type information and perform class casting

   PrivateKey privKey = ...;
   if (privKey instance of RSAPrivateKey) {
       RSAPrivateKey rsaPrivKey = (RSAPrivateKey)privKey;
   if (privKey instance of DSAPrivateKey) {
       DSAPrivateKey dsaPrivKey = (DSAPrivateKey)privKey;
   if (privKey instance of ECPrivateKey) {
       ECPrivateKey ecPrivKey = (ECPrivateKey)privKey;
   }