Cipher

You apply a thin layer of the clear diamond infused ink all over a chosen text while imbuing it with potent illusion magic, enchiphering it into unreadable, flickering runes. At the same time, you create a powerful bond between the cipher and a delicate gemstone, which will act as a translation key to the holder.

The text becoms unreadable to anyone who isn't holding the key, even creatures with truesight. Spells of 3rd level and below that allows creatures to read thing they usually cannot, has no effect on this text. A creature holding the key can read the text clearly. Furthermore, a creature holding the key and the enchiphered text can use an action to crush the gem and end the spell.