The progress bar will reset to the start, and gradually move up again to track the progress of the key generation. Wave the mouse in circles over the blank area in the PuTTYgen window, and the progress bar will gradually fill up as PuTTYgen collects enough randomness. You don't need to wave the mouse in particularly imaginative patterns (although it can't hurt); PuTTYgen will collect enough randomness just from the fine detail of exactly how far the mouse has moved each time Windows samples its position.When the progress bar reaches the end, PuTTYgen will begin creating the key.
The numbers 65 and 90 are magic numbers, since at their definition there is no hint that they refer to Unicode code points. Instead of these numbers, write 'A' and 'Z'. Then, hope that your program will never run on IBM machines, since your passwords would contain characters other than uppercase letters. Some of the additional classes that I had to write to support the license key generation are a random number generator, a data type parser, a number display class, and a checksum class. The random number class uses the C# Random class but adds some additional methods to support the requirements.