store password in AIR app

hi, I'm developing an AIR  application and I need to store password there so user don't have to  write it everytime when he launch the application. I want to ask you if  you know some way how to store the password in no plain string. I can  store it in the file but everybody can read it there... Is there any way  how to encrypt and then decrypt saved password? (I'm using AS3)

thanks