ComputerCraft modEM API

--[[
        modEM

    A custom peripheral API wrapper.

    This API is specifically made to create secure connections between two computers.


    How it works:
    You specify a channel for the connection, the 2nd computer connects to it.
    Ones the API recognizes a 2nd connection, it generates a random number (between 1 and 65535) and passes it to the 2nd computer.
    It then generates a random string, containing symbols and numbers, and passes that to the 2nd computer too.
    The API then closes the channel and opens a new one using the new generated number.
    The 2nd computer connects to that using the number the API gave him.
    Now why is that all necessary?
    It passes a random number and opens a new channel on that to prevent from a 3rd party being able to listen on it.
    Sure he can guess the number but it'd need a while.

    It also passes a random string to the 2nd computer, because it ENCRYPTS the messages using that string.
    Which leads to a higher security if a 3rd party is listening on that channel too.



    This is mainly made for future secret projects :)

    ~Piorjade 2016

]]

--[[
      THIS IS THE ENCRYPTION API MADE BY "PixelToast"
]]

local function zfill(N)
    N=string.format("%X",N)
    Zs=""
    if #N==1 then
        Zs="0"
    end
    return Zs..N
end

local function serializeImpl(t)
    local sType = type(t)
    if sType == "table" then
        local lstcnt=0
        for k,v in pairs(t) do
            lstcnt = lstcnt + 1
        end
        local result = "{"
        local aset=1
        for k,v in pairs(t) do
            if k==aset then
                result = result..serializeImpl(v)..","
                aset=aset+1
            else
                result = result..("["..serializeImpl(k).."]="..serializeImpl(v)..",")
            end
        end
        result = result.."}"
        return result
    elseif sType == "string" then
        return string.format("%q",t)
    elseif sType == "number" or sType == "boolean" or sType == "nil" then
        return tostring(t)
    elseif sType == "function" then
        local status,data=pcall(string.dump,t)
        if status then
            return 'func('..string.format("%q",data)..')'
        else
            error()
        end
    else
        error()
    end
end

local function split(T,func)
    if func then
        T=func(T)
    end
    local Out={}
    if type(T)=="table" then
        for k,v in pairs(T) do
            Out[split(k)]=split(v)
        end
    else
        Out=T
    end
    return Out
end

local function serialize( t )
    t=split(t)
    return serializeImpl( t, tTracking )
end

local function unserialize( s )
    local func, e = loadstring( "return "..s, "serialize" )
    local funcs={}
    if not func then
        return e
    end
    setfenv( func, {
        func=function(S)
            local new={}
            funcs[new]=S
            return new
        end,
    })
    return split(func(),function(val)
        if funcs[val] then
            return loadstring(funcs[val])
        else
            return val
        end
    end)
end

local function sure(N,n)
    if (l2-n)<1 then N="0" end
    return N
end

local function splitnum(S)
    Out=""
    for l1=1,#S,2 do
        l2=(#S-l1)+1
        CNum=tonumber("0x"..sure(string.sub(S,l2-1,l2-1),1) .. sure(string.sub(S,l2,l2),0))
        Out=string.char(CNum)..Out
    end
    return Out
end

local function wrap(N)
    return N-(math.floor(N/256)*256)
end

local function checksum(S,num)
    local sum=0
    for char in string.gmatch(S,".") do
        for l1=1,(num or 1) do
            math.randomseed(string.byte(char)+sum)
            sum=sum+math.random(0,9999)
        end
    end
    math.randomseed(sum)
    return sum
end

local function genkey(len,psw)
    checksum(psw)
    local key={}
    local tKeys={}
    for l1=1,len do
        local num=math.random(1,len)
        while tKeys[num] do
            num=math.random(1,len)
        end
        tKeys[num]=true
        key[l1]={num,math.random(0,255)}
    end
    return key
end

local function encrypt(data,psw)
    data=serialize(data)
    local chs=checksum(data)
    local key=genkey(#data,psw)
    local out={}
    local cnt=1
    for char in string.gmatch(data,".") do
        table.insert(out,key[cnt][1],zfill(wrap(string.byte(char)+key[cnt][2])),chars)
        cnt=cnt+1
    end
    return string.sub(serialize({chs,table.concat(out)}),2,-3)
end

local function decrypt(data,psw)
    local oData=data
    data=unserialize("{"..data.."}")
    if type(data)~="table" then
        return oData
    end
    local chs=data[1]
    data=data[2]
    local key=genkey((#data)/2,psw)
    local sKey={}
    for k,v in pairs(key) do
        sKey[v[1]]={k,v[2]}
    end
    local str=splitnum(data)
    local cnt=1
    local out={}
    for char in string.gmatch(str,".") do
        table.insert(out,sKey[cnt][1],string.char(wrap(string.byte(char)-sKey[cnt][2])))
        cnt=cnt+1
    end
    out=table.concat(out)
    if checksum(out or "")==chs then
        return unserialize(out)
    end
    return oData,out,chs
end

--[[
  ENCRYPTION API ENDS HERE

]]
local chan = 0
local encryption = "abc"
local isConnected = false

local function makeString(l)
        if l < 1 then return nil end -- Check for l < 1
        local s = "" -- Start string
        for i = 1, l do
            n = math.random(32, 126) -- Generate random number from 32 to 126
            if n == 96 then n = math.random(32, 95) end
                s = s .. string.char(n) -- turn it into character and add to string
        end
        return s -- Return string
end

function open(side)
  if modem then
    return false, "modemWrapped"
  end
  modem = peripheral.wrap(side)
end

function close()
  modem.closeAll()
  isConnected = false
  chan = 0
  encryption = "abc"
  modem = nil
end

function host(startingChannel, side, timout)
  if modem then
    return false, "modemWrapped"
  end
  if type(timeout) == "number" then
    local timerID = os.startTimer(timeout)
  end
  if startingChannel == nil or startingChannel < 1 or startingChannel > 65535 then
    startingChannel = os.getComputerID()
  end
  chan = startingChannel
  if type(side) ~= "string" then return false end
  open(side)
  modem.open(chan)
  while true do
    local ev, a, b, c, msg, dis = os.pullEvent()
    if ev == "modem_message" and msg == "Connected." then
      local tab = {
        msg = "ok",
        newPort = 1,
        decPass = "abc",
      }
      tab.newPort = math.random(1, 65535)
      tab.decPass = makeString(6)
      encryption = tab.decPass
      modem.transmit(chan, chan, textutils.serialize(tab))
      modem.close(chan)
      chan = tab.newPort
      modem.open(chan)
      isConnected = true
      break
    elseif ev == "timer" and a == timerID then
      close()
      return false, "timeout"
    end
  end
end

function connect(startingChannel, timeout)
  if modem == nil then return false, "No opened modem." end
  if type(timeout) == "number" then
    local timerID = os.startTimer(timeout)
  end
  chan = startingChannel
  modem.closeAll()
  modem.open(chan)
  modem.transmit(chan, chan, "Connected.")
  while true do

    ev, side, sendChan, repChan, msg, distance = os.pullEvent()

    if ev == "modem_message" then
      msg = textutils.unserialize(msg)
      if msg.msg == "ok" then
        modem.closeAll()
        chan = msg.newPort
        modem.open(chan)
        encryption = msg.decPass
        break
      end
    elseif ev == "timer" and side == timerID then
      close()
      return false, "timeout"
    end
  end
  isConnected = true
end

function receive(timeout)

  if not isConnected then
    return false, "noConnection"
  end
  if not modem then return false, "No opened modem." end
  if type(timeout) == "number" then
    local timerID = os.startTimer(timout)
  end
  while true do
    local ev, a, b, c, msg, dis = os.pullEvent()
    if ev == "timer" and a == timerID then
      return false, "timeout"
    elseif ev == "modem_message" and msg ~= nil then
      return decrypt(msg, encryption)
    end
  end
end

function send(msg)
  if not isConnected then
    return false, "noConnection"
  end
  if not modem then return false, "No opened modem." end
  modem.transmit(chan, chan, encrypt(msg, encryption))
  return
end