protected <T extends KeySpec> T engineGetKeySpec(Key key, Class<T> keySpec)
     throws InvalidKeySpecException {
   try {
     // convert key to one of our keys
     // this also verifies that the key is a valid RSA key and ensures
     // that the encoding is X.509/PKCS#8 for public/private keys
     key = engineTranslateKey(key);
   } catch (InvalidKeyException e) {
     throw new InvalidKeySpecException(e);
   }
   if (key instanceof RSAPublicKey) {
     RSAPublicKey rsaKey = (RSAPublicKey) key;
     if (rsaPublicKeySpecClass.isAssignableFrom(keySpec)) {
       return keySpec.cast(new RSAPublicKeySpec(rsaKey.getModulus(), rsaKey.getPublicExponent()));
     } else if (x509KeySpecClass.isAssignableFrom(keySpec)) {
       return keySpec.cast(new X509EncodedKeySpec(key.getEncoded()));
     } else {
       throw new InvalidKeySpecException(
           "KeySpec must be RSAPublicKeySpec or " + "X509EncodedKeySpec for RSA public keys");
     }
   } else if (key instanceof RSAPrivateKey) {
     if (pkcs8KeySpecClass.isAssignableFrom(keySpec)) {
       return keySpec.cast(new PKCS8EncodedKeySpec(key.getEncoded()));
     } else if (rsaPrivateCrtKeySpecClass.isAssignableFrom(keySpec)) {
       if (key instanceof RSAPrivateCrtKey) {
         RSAPrivateCrtKey crtKey = (RSAPrivateCrtKey) key;
         return keySpec.cast(
             new RSAPrivateCrtKeySpec(
                 crtKey.getModulus(),
                 crtKey.getPublicExponent(),
                 crtKey.getPrivateExponent(),
                 crtKey.getPrimeP(),
                 crtKey.getPrimeQ(),
                 crtKey.getPrimeExponentP(),
                 crtKey.getPrimeExponentQ(),
                 crtKey.getCrtCoefficient()));
       } else {
         throw new InvalidKeySpecException("RSAPrivateCrtKeySpec can only be used with CRT keys");
       }
     } else if (rsaPrivateKeySpecClass.isAssignableFrom(keySpec)) {
       RSAPrivateKey rsaKey = (RSAPrivateKey) key;
       return keySpec.cast(
           new RSAPrivateKeySpec(rsaKey.getModulus(), rsaKey.getPrivateExponent()));
     } else {
       throw new InvalidKeySpecException(
           "KeySpec must be RSAPrivate(Crt)KeySpec or "
               + "PKCS8EncodedKeySpec for RSA private keys");
     }
   } else {
     // should not occur, caught in engineTranslateKey()
     throw new InvalidKeySpecException("Neither public nor private key");
   }
 }
 /**
  * Translate an RSA key into a SunRsaSign RSA key. If conversion is not possible, throw an
  * InvalidKeyException. See also JCA doc.
  */
 protected Key engineTranslateKey(Key key) throws InvalidKeyException {
   if (key == null) {
     throw new InvalidKeyException("Key must not be null");
   }
   String keyAlg = key.getAlgorithm();
   if (keyAlg.equals("RSA") == false) {
     throw new InvalidKeyException("Not an RSA key: " + keyAlg);
   }
   if (key instanceof PublicKey) {
     return translatePublicKey((PublicKey) key);
   } else if (key instanceof PrivateKey) {
     return translatePrivateKey((PrivateKey) key);
   } else {
     throw new InvalidKeyException("Neither a public nor a private key");
   }
 }