Where to save customer-adresses safty...

Hello ! I have a form, where a customer can input his address. Often, customers come back and the form is empty, they have to re-enter the address. What's the safest way to save the customer-address ? 1.) Setting a cooking, which "points" to a file on my web-server. The directory is protected via .htaccess. 2.) Same as 1.), but letting the user have a password to access the file. 3.) Crypting the address and storing it directly into a cookie. 4.) Letting the user logging on with login/pasword (without setting anything in the browser) Regards Martin