Thomas Jefferson received a coded message from a friend claiming the code would: "defy the united ingenuity of the whole human race."

Arranging the "united ingenuity of the whole human race" might be trickier than the code, but it was a decent code, considering it took a modern computer 100,000 calculations using equally modern techniques, such as frequency analysis of 2-letter combinations gathered from documents of the time.

The Newsvine article gives the details of the encryption method, which was used later for diplomatic communication. The method is quite accessible, involving reordering the characters and inserting random numbers of extra characters.

Perhaps you can use it to encrypt your parental control passwords.