Lua：针对特定场景的一小段代码

```lua
local function my_poor_cryptography(s)
   local codes = {}
   -- string to numbers
   for c in s:gmatch"%a" do
      table.insert(codes, c:byte() - (c:find"%l" and 96 or 64))
   end
   -- math here (https://en.wikipedia.org/wiki/ROT13)
   for j = 1, #codes do
      codes[j] = (codes[j] + 12) % 26 + 1
   end
   -- numbers to string
   s = s:gsub("%a",
      function(c)
         return c.char(table.remove(codes, 1) + (c:find"%l" and 96 or 64))
      end)
   return s
end

使用方法：

local str = "Hello, World!"
str = my_poor_cryptography(str)
print(str)     --> Uryyb, Jbeyq!
str = my_poor_cryptography(str)
print(str)     --> Hello, World!

```