I did this in Creative Mode, and I shall do it again here.
With the recent addition of Redstone circuitry to Minecraft Alpha, and with Multiplayer right around the corner, I figured I'd make an Alpha version of my order-sensitive lock.
There are plenty of combination locks out there, but this one is much different. Instead of having to turn certain levers on and others off, you need to press all the buttons in the correct order.
I didn't use any hacks or cheats whatsoever to make this. Everything you see in this video was obtained through mining and crafting, so I had to limit this to only two buttons. This system could, however, have an unlimited amount of buttons in whichever order you want, provided you have enough materials and free space.
Keep in mind that this is a proof of concept. If you don't know what that is, it's basically proof that systems like this could feasibly be put to use. Thus, it's oversized, not much to look at, and likely overcomplicated. I'll keep working to make a better version with more buttons.
Couldn't tell if yours was along the same lines. I'm sort of new to this logic gate stuff so I'm not sure if there's a simpler way to do what I did. In theory with mine I can just stack another AND/RSNAND combo on to add another number to the combination.
The order for the picture is obviously 1,2,3.
I have successfully made this circuit and I made another one which used latches and pressure plates/ buttons.
Getting the circuit into a workable area is much different.
As for security I make my circuit inside my base with a line to a secure area around the switches themselves which has a couple layers of obsidian with lava sandwiched between them.
EDIT: forgot to mention that with the latch/button/pressure plate method a reset button is also needed. It is possible to make it so that any wrong combination would reset but it would require a massive amount of circuitry. Easiest just to make a resent button.
There are quite a few ways to prevent tnting from working. First, you could have a stash of items surounded by a moat of lava. There would be only one way to the bridge and the only method of getting across is thru the locks. And if locks fail, bridge collapses. Im very certain we can make collapsing bridges. So locks can be used.
it doesn't have RSNAND specifically so you'll have to make it yourself from two NANDs but it lets you play with them in a user friendly environment before tackling the miserable task of building them in 3D in minecraft.