Yes, and it's partially implemented as a grid. Read this:
http://chdk.wikia.com/wiki/Grids#--_Authorized-Use_OnlyIt doesn't give you the possibility to lock the camera and unlock it by a specified buttons, but you might use this thing with a kind of script. Scripting in uBasic or LUA is very simple and if you like to enhance your camera it's good to learn one of them;)
I guess the other way to "lock" camera is to use script which would do things like this:
- set the screen console to full-screen [set_console_layout(0,0,40,13) --I'm not sure about numbers]
- write some message like: print("Camera is locked!!!")
- wait for specified clicks to unlock
- in a case of good sequence - end the script to give you usual control
- in a case of few bad clicks start blinking all leds and play random sounds:D
Remember, that all these things will only appear if CHDK is loaded. So one can only remove SD card or format it and the whole anti-thetf system is useless.
