Hiding messages in quantum data

A method is proposed to hide messages in arbitrary quantum data files. The messages may act as “watermarks,” to secure the authenticity and/or integrity of the data. With the help of classical secret keys, they can be made unreadable by other parties and to reveal whether thay have been tampered with. The basic idea is to encode the data using a quantum error-correcting code and hide the message as (correctible) errors, deliberately inserted, which can be read out from the error syndrome. Also discussed briefly is a “reverse encoding,” which would involve putting the actual data in the error syndrome, and letting the encoded qubit itself carry the message.