Originally posted by wolfgang59
. . . Lets presume the Original Poster intended simple substitution . . .
That is what I meant.
There are all sorts of difficulty levels. Substitution or the use of keys or whatever you can think of will work.
This is easy: sfeipuqbxo = 17-5-4-8-15-20-16-1-23-14 = redhotpawn
Why don't we all use our imaginations a little bit?
I've already written one which is quite simple.
As wolfgang59 has stated, a bit of logical analysis paired with time will make many invented cipher's both possible and entertaining to solve.