If we assume that you are having numerical input to some other part of your process, then you have the facility in your code >
Type passnumber
If passnumber = password number thats it.


If you don't have numerical input, then you need a little state machine.
Start.
If key = 1st digit then statecount:=1 else statecount:=0
If key = 2nd digit then statecount:=2 else statecount:=0
If key = 3rd digit then statecount:=3 else statecount:=0
If key = 4th digit then statecount:=4 else statecount:= 0
If key = ent and statecount >=4 then unlocked :=true;

Steve