Okay, within the context of this discussion I will accept that secure and unbreakable are interchangeable terms, with the stipulation that it is understood that secure or unbreakable are relative terms bounded by a finite period of time.
You realize of course that STU communications are based on DES. So to answer you last question first, yes, my home computer bought at PC World has many orders of magnitude more processing power than the STU phone I used.
The NSA has spent millions of dollars on a replacement for DES. It is called AES. WPA does support AES; I am using AES on my home network.
So, let's cut to the chase...
I have a home Wi-Fi setup consisting of a router and three computers in radio contact with each other. I am using DHCP to assign IP addresses to the computers. I am not using MAC filtering. I am transmitting my SSID address "HACKME" ten times a second. I have WPA PSK using AES. My passphrase is successor?