declare function MV_ENC_STR(str: string, encryptKey: string, decryptKey: string): string

will encrypt the passed string constant with the provided encryptKey. Then decryptKey is evaluated at runtime to grab the key. There are no restrictions on the length or the allowed characters of the keys, only that they are the same.

Valid Usage 

local getKey = MV_VM(function()
  return "pass" .. "word123"
end)

return MV_ENC_STR("hello world", "password123", getKey())