solver, also known as a substitution cipher. This is the kind of puzzle
where A is N, B is O, C is P, etc. It can also be called a cryptoquip
or a cryptogram in the local newspaper.
To use it, you just define a "key" and the letters in the upper part will
be translated and shown in the lower part. This is only a tool to
help you out – it can not automatically solve the puzzle for you.
In a related vein, you can check out the ROT13 encoder which
swaps letters from the first half of the alphabet with the second half (and
vice versa), or the Caesar cipher where you
essentialy "slide" the alphabet over to the left or right.
Keyed Caesar alphabet:
Or a decode alphabet: ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789