There is a provably unbreakable cipher called a one$-$time pad. The way it works is you

shift each character of the message by a random amount between $1$ and $26$ characters,

wrapping around the alphabet if necessary. For instance, if the current character is y

and the shift is $5,$ then the new character is d$.$ Each character gets its own shift, so

there needs to be as many random shifts as there are characters in the message. As an

example, suppose the user enters secret. The program should generate a random shift

between $1$ and $26$ for each character. Suppose the randomly generated shifts are $1,3,$

$2,10,8,$ and $2.$ The encrypted message would be thebmv.