2 methods come to mind;
Quartz memory discs. They are a are currently existing technology that will store information for close to 12 billion years! - The problem? Designing a reader or instructions for building a reader that will last as long.
Carve/mark giant symbols on the moons surface pointing to a secure storage facility there containing information engraved on metal tablets or some other system that can survive being buried in a underground chamber in a vacuum for the period required. - The problem? Getting there to recover the info.