This is a simple tutorial on how to make a door that requires a password.
 Basic Design
Follow these steps carefully.
 Step 1
First place an 11 block row of any block. Then add a row of 8 on both sides. Then add another Row of 11 on top of the first.
 Step 2
Add switches on the BOTTOM row, followed by signs on the second, each with a number in order (1,2,3 etc.)
 Step 3
Next add a redstone repeater for each block in front of a switch.
 Step 4
According to the password you want (1, 2, 6 is used in the example) you need to place a block in front of the switches that make up your password and put a redstone torch on top of each. The password is 1,2,6. Therefore each block is placed in front of switches 1,2 and 6.
 Step 5
Next, 1 more block to each, in front of the ones you just added. And fill the spaces with redstone repeater.
 Step 6
Add redstone wire on blocks pointed out in the picture:
 Step 7
Place a strand of redstone wire, starting from the middle, down to the 2nd last block. At the last row, place one block in front of the redstone wire strand.
 Step 8
Add one redstone torch on top of the block just added. Then add another block on top. After which, add an iron or wood door on top of that block. (Be careful, if you're trying to guard your stuff on a PVP server, one might just craft a button and ruin the whole point of a passlock)
 Step 9
You're done! All you need to do is turn on the switches that make up your password, then the door will open. The password used here is 1,2,6. Therefore to open the door, the levers 1,2 and 6 need to be on, with all the others off.
 Step 10
Add Blocks on top.