code: public static byte[] changePassphrase(CryptorProvider cryptoProvider, byte[] masterkey, byte[] pepper, CharSequence oldPassphrase, CharSequence newPassphrase) throws InvalidPassphraseException {
  		final KeyFile keyFile = KeyFile.parse(masterkey);
  		try (Cryptor cryptor = cryptoProvider.createFromKeyFile(keyFile, oldPassphrase, pepper, keyFile.getVersion())) {
  			return cryptor.writeKeysToMasterkeyFile(newPassphrase, pepper, keyFile.getVersion()).serialize();
  		}
  	}
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 pepper An application-specific pepper added to the salt during key-derivation (if applicable)
  @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 1.1.4