Lock for ComputerCraft (Minecraft mod)

lock.lua

--
-- This is a program to lock a chest/door with computercraft
-- Made by Esa Varemo
--

--
-- NOTE: This file must be named 'startup', for the computer to load the program on startup
--

file = io.open("password","r")
pwd = file:read()

file = io.open("admin_pwd","r")
admin_pwd = file:read()

local function clear()
    term.clear()
    term.setCursorPos(1,1)
end

local function reDraw()
    clear()
    write(prompt)
end

prompt = "Password:\n>>"

reDraw()

answer = ""
run = true
while run do
    event, key = os.pullEventRaw()
    if event == "char" then
        answer = answer .. key
        prompt = prompt .. "*"
        reDraw()
    elseif key == 14 then -- BACKSPACE
        if string.len(answer) >= 1 then
            answer = string.sub(answer, 1, -2)
            prompt  = string.sub(prompt , 1, -2)
            reDraw()
        end
    elseif key == 28 then -- ENTER
        if answer == pwd then
            clear()
            write("Correct!")
            redstone.setOutput("back",true)
            sleep(3)
            redstone.setOutput("back",false)
            os.shutdown()
		elseif answer == admin_pwd then
			clear()
            run = false
        else
            clear()
            print("Wrong")
            sleep(1)
            os.reboot()
        end
    end
end