Is it possible to encrypt or make sure that the indexed IOTA messages are received/extracted only by receiver they are meant for. My user case: User A, B, and C each have IDs that are known to all users (A,B,C in this case). Now user A want to send a message to B, so A will use B's ID as an index and attach the message to the tangle. User B will be looking for messages on the tangle that have B's ID as index and will be able to extract it. How could I make sure that only user B is able to extract this indexed data (and not User C, if user C decide to look for the same index)? Are there any other IOTA options?