Today I've found this interesting circuit, which In use Dallas/Maxim's iButton as a key to an electronic lock.

This circuit is built on the Atmel's 89C2051 MCU. This electronic lock can be used with any type of iButtons you may already have, since the only thing needed is the internal serial number, that's different for every iButton. The command used to read the serial number is the same for all iButtons. The iButton family code that goes with every iButton, can be anything and is calculated as part of the whole serial number.

This electronic lock designed to work stand-alone and it's easy to construct. What the user sees (outside of the door for example) is a iButton socket and a led. From inside the door, we can open it using a simple push button. For the actual lock of the door a solenoid and a bold are used. Solenoid must be rated at 12Vdc. iButtons serial numbers stored in memory can be removed and updated when needed. One master key is used to manage the rest of them. Totally a number of 9 different keys can be stored in memory.