From what was a Wikipedia Category Unsolved Ciphers and is now included in Undeciphered Historical codes and ciphers - 'A list of unsolved problems that are, or are thought to be, codes or ciphers.'

There are many websites on the subject of uncracked codes and ciphers - eg [2], [3] and the Elonka's List page [4]. The lists share many entries in common.

See also Undeciphered writing systems