code: public static byte[] changePassphrase(CryptorProvider cryptoProvider, byte[] masterkey, CharSequence oldPassphrase, CharSequence newPassphrase) throws InvalidPassphraseException {
  		return changePassphrase(cryptoProvider, masterkey, new byte[0], oldPassphrase, newPassphrase);
  	}
docs: Reencrypts a masterkey with a new passphrase.
  
  @param cryptoProvider A suitable CryptorProvider instance, i.e. same version as the original masterkey has been created with.
  @param masterkey The original JSON representation of the masterkey
  @param oldPassphrase The old passphrase
  @param newPassphrase The new passphrase
  @return A JSON representation of the masterkey, now encrypted with <code>newPassphrase</code>
  @throws InvalidPassphraseException If the wrong <code>oldPassphrase</code> has been supplied for the <code>masterkey</code>
  @since 1.1.0
  @see #changePassphrase(CryptorProvider, byte[], byte[], CharSequence, CharSequence)