Better Simple Encoding

local function code(msg, key, mode, fileMode, convertNums)
    if convertNums then
        nm = ""
        for i = 1, math.floor(#msg/3), 1 do
            os.queueEvent("NCY")
            os.pullEvent("NCY")
            nm = nm .. string.char(tonumber(string.sub(msg,i*3-2,i*3)))
        end
    end
    key = tostring(key)
    msg = tostring(msg)
    if convertNums then msg = nm end
    local kn = 1
    local nmsg = ""
    for i = 1, #msg do
        if i % 50 == 0 then
            os.queueEvent("NO-CRASH-YIELD")
            os.pullEvent("NO-CRASH-YIELD")
        end
        curChar = string.sub(msg, i, i)
        nCurChar = string.byte(curChar)
        curKey = string.sub(key, kn, kn)
        nCurKey = string.byte(curKey)
        if mode == "encode" then
            newChar = nCurChar + nCurKey
        elseif mode == "decode" then
            newChar = nCurChar - nCurKey
        end
        if newChar >= 256 then
            newChar = newChar - 255
        end
        if newChar <= 0 then
            newChar = newChar + 255
        end
        if not fileMode then
            nmsg = nmsg .. string.char(newChar)
        else
            nc = tostring(newChar)
            while #nc < 3 do
                nc = "0"..nc
            end
            nmsg = nmsg .. nc
        end
        if kn == #key then
            kn = 1
        else
            kn = kn+1
        end
    end
    return nmsg
end

function encode(msg, key, doFile, convertNums)
    return code(msg, key, "encode", doFile, convertNums)
end

function decode(msg, key, doFile, convertNums)
    return code(msg, key, "decode", doFile, convertNums)
end