how am i going to convert my input password into asterisk or circle or anything so that i can hide my password in my game?

you need an invisible input field (called shadow input or something like that) and a normal text that you're filling with *'s in the length of your string.

why not just use a font with only symbols, instead of creating an inkey field and a starfield??

because this wouldnt hide you password from someone who is looking about your shoulders -.-

that idea is actually quite good, just use a font with only bullets as characters and you're done.