well to start unless you are using some SERIOUS encryption methods you wont need anything nearly as large as a 1GB, in fact you would probably be better with a smaller one since it will be easier to read by a microcontroller.
On that note, you will need a microcontroller, that has the ability to read a USB stick (PIC or Arduino should be fine). Then it will just be a matter of programming it to read and inspect a text file, and then turn a deadbolt with a motor/servo. I would start with that first before moving into encryptions, though having a specific file on a specific sized flash drive should be enough encryption.
You are going to need a fairly significant power supply to drive the servo, as deadbolts can be a little tought to turn, and even more so if you want to control it via 3g/text message (much more)
An interesting thought I just had was if you were to have it set up so that you could plug in a flash drive, have it read the file and use that as the current "password" so to speak, and then have it look for that file when you come back, that way its set everytime you leave, and its "encrypted" essentially.