gistfile1.lua

function Demo()
charset = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
   local value = ""
      math.randomseed(os.time())
      for i = 1, math.random(1, 100) do
         rand = math.random(#charset)
         value = value.. string.sub(charset, rand, rand)
      end
   return value
end

local function caesar(input, shift)
   input = input:gsub("%s", Demo())
   return input:gsub("%a", function(x)

   local test = (x:lower() == x and string.byte('a') or string.byte('A'))
   local crypt = x:byte() - test  
   crypt = crypt + (shift)
   crypt = crypt%26
   crypt = crypt + test
   return string.char(crypt)
   end)
end

local function decrypt(input, shift)
   local decrypt =  caesar(input, -shift)
   return (decrypt:gsub(Demo(), function(text) return " " end))
end


function read()
    local f = io.open("test.txt", "r")
    content = f:read("*all")
    f:close()
    return content
end


-- Test
do
	local input = read()
	io.write("Digite o shift: ")
	local shift = io.read() 
	local e = caesar(input, shift)
	local d = decrypt(e, shift)

	local f = io.open("crypt.txt", "w")
    local x = f:write(e)
    f:close()
	print("Texto Original: ", input) -- testing purposes

	print("Texto criptografado: ", e) -- testing purposes

	local fp = io.open("descrypt.txt", "w")
    local z = fp:write(d)
    fp:close()
	print("Texto descriptografado: ", d) -- testing purposes
end