How to enter password and normal character in one textbox like *****6789

Hi All,
           I have a textbox in which I want to be enter normal character as well as password character like *****6789.
My TextBox accept 9 character in which 5 will not be readable and when user will type it will show * and last 4 character will be display as it is. suppose I have enter 123456789 and so it should be display like *****6789 and suppose I delete 5 character 5 so 6 should be come into 5th place and it will be convert to non readable (*) like *****789.
How I can achieve such functionality for my Textbox in as ...