[ydkme]

Store it on the Bitcoin blockchain in the OP_RETURN field [1][2]. Note that this is considered an abuse of the system and discouraged, but of all the systems available now, Bitcoin is most likely to still be around in some form in 500 years IMO.

[1] https://bitcoin.stackexchange.com/questions/39347/how-to-sto...

[2] http://www.righto.com/2014/02/ascii-bernanke-wikileaks-photo...