How to restrict the length of a string to a fixed length

[tmd63]

I want to have 2 cells with any length text in both.
I want some VBA code to combine and modify a third text box with a fixed length string that has a fixed length (say 8 characters) and the output characters can contain upper, lower case characters , numbers and special characters by return.
And the entry text fields can contain extra characters and numbers like those used in a website field.
However, the output text/numbers MUST be repeatable with the same entry fields.
So for example [www.mrexcel.com/board/forums/excel-questions] and [test01] always returns [DgT%£Hg38].
The first and second fields can be any length, but the third field MUST always be a fixed length of say 8 or 12 characters, but even smaller fields of [mrexcel] and [test01] returns 8 characters ([E4%hTf7i]) for example (note this time the fields are 7 and 6 characters long but the output field is 8 characters).
But each entry is not stored and the fields give a different output, but only if there is a different string used (not a random number generation)!