code: public static PrivateKey readPrivateKey(final File file) throws IOException,
  		NoSuchAlgorithmException, InvalidKeySpecException, NoSuchProviderException
  	{
  		return readPrivateKey(file, KeyPairGeneratorAlgorithm.RSA.getAlgorithm());
  	}
docs: Reads the given {@link File}( in *.der format) with the default RSA algorithm and returns the
  {@link PrivateKey} object.
  
  @param file
  the file( in *.der format) that contains the private key
  @return the {@link PrivateKey} object
  
  @throws IOException
  Signals that an I/O exception has occurred.
  @throws NoSuchAlgorithmException
  is thrown if instantiation of the cypher object fails.
  @throws InvalidKeySpecException
  is thrown if generation of the SecretKey object fails.
  @throws NoSuchProviderException
  is thrown if the specified provider is not registered in the security provider
  list.