 <blockquote> <p>Can i now go and change the position of the characters in the string?</p> </blockquote> <p>No. Strings in .NET are immutable – they cannot be changed. In order to modify a string in VB, you call a function which creates a <em>new</em> string based off the modified contents of the old string. That’s what all the <a href="http://msdn.microsoft.com/en-us/library/system.string_methods.aspx" rel="nofollow">string methods</a> are doing.</p> <p>It’s not entirely clear what your encryption function is supposed to do though. It seems to permute the letter positions, but what schema does it use for that?</p>