Problem Decrypting String To Test If A Valid Table Exists

local contains = function(tbl,val)
  for k,v in pairs(tbl) do
	if v == val then return true end
  end
  return false
end

local hash = function(str)
  local out = {}
  for s in str:gmatch(".") do
	if not contains(out,s) then out[#out+1] = s end
  end
  return table.concat(out)
end

local encryption = function(decrypt,plainTXT,key,password)
  local cipher,cipherTXT = "",""
  local base = 'AaBbCcDdEeFfGgHhIiJjKkLlMmNnOoPpQqRrSsTtUuVvWwXxYyZz0123456789=+[]{}-_,." '

  if key ~= nil and key > #base then  -- keep key within bounds of base length
	key = key % #base
  end

  if password ~= nil then  -- place password at front of encryption without duplicates	
	cipher = hash(password)
  end

  for i=1,#base do -- create the cipher
	local CHAR = string.sub(base,(key+i)%#base,(key+i)%#base)

	if password ~= nil then
	  for I=1,#password do -- find the same letter in password & remove it
		local pasChar = string.sub(password,I,I)

		if pasChar == CHAR then
		  CHAR = ""
		end
	  end
	end
	cipher = cipher..CHAR
  end

  if type(plainTXT) == "table" then
	plainTXT = textutils.serialize(plainTXT)
  end

  for i=1,#plainTXT do -- loop through text for encryption
	local letter = string.sub(plainTXT,i,i)

	for I=1,#base do
	  local baseKey = string.sub(base,I,I)
	  local hashKey = string.sub(cipher,I,I)

	  if decrypt == true then -- if decrypting flip flop baseKey & hashKey
		if letter == hashKey then
		  cipherTXT = cipherTXT..baseKey
		end
	  else
		if letter == baseKey then -- encrypt baseKey with hashKey
		  cipherTXT = cipherTXT..hashKey
		end
	  end
	end
  end
  return cipherTXT
end

local keys = {6,117,24,48,372}
local pass = {"squIrrel","ClasSic","BlankeT","challenger"}

local m = peripheral.wrap("top")
m.open(2)

while true do
  local ev = { os.pullEvent() }
  local bfD = ""
  local pkg = {}

  if ev[1] == "modem_message" then
	local rawData = ev[5]

	for i=1,#keys do
	  for I=1,#pass do
		bfD = encryption(true,rawData,keys[i],pass[I])

		local isTable = textutils.unserialize(bfD)
		if type(isTable) == "table" and isTable["ptl"] and isTable["cid"] then
		  pkg["data"] = isTable
		  pkg["key"] = keys[i]
		  pkg["pwd"] = pass[I]
		end
	  end
	end
  end

  print(pkg["data"])
  print("Decrypted w/: "..pkg["key"].."  |"..pkg["pwd"])
end

ElvishJerricco, on 08 October 2013 - 05:44 AM said:

Ok when you say you're sending "{ptl="cConnect",cid=os.getComputerID(),data={},}" over the network, are you doing

local s = '{ptl="cConnect",cid=os.getComputerID(),data={},}'
send(s)

or

local t = {ptl="cConnect",cid=os.getComputerID(),data={},}
send(textutils.serialize(t))

If it's the first, the problem is that you're sending a string which calls the function os.getComputerID() when it gets loaded. Problem is, textutils.unserialize doesn't let the loaded table call any APIs, so that "os" table it's trying to index is nil.

jay5476, on 08 October 2013 - 05:54 AM said:

you can actually send tables over rednet so you can do

rednet.send(id,{table1={"moretables"}})

and that should work perfectly fine if your having trouble try loading the table before sending it eg.

yourtable = {tableinfo}
rednet.send(id,yourtable)

Bomb Bloke, on 08 October 2013 - 08:50 PM said:

You attempt to unserialise whatever your decryption attempt returns before deciding whether the decryption was successful, resulting in random gibberish being passed to textutils. Gibberish which can potentially take the form of an equation it may try to resolve, resulting in referrences to variables that don't exist and hence random error messages from the interpretor.

Obviously textutils shouldn't do this, but your answer is to implement your own "does this string represent a table?" check before you try and unserialise.

AgentE382, on 08 October 2013 - 10:46 PM said:

Yeah, basically your encryption function is broken. You don't check its results, either. You should probably do that and add some debug prints to tell you exactly where your encryption function is going wrong.

Or, you could just switch to a real encryption algorithm that has been thoroughly tested. Someone here's got an AES implementation, I've got RC4, and I've seen a few other real algorithms in pure Lua elsewhere on the net.

Bomb Bloke, on 09 October 2013 - 01:13 AM said:

Cozzimoto, on 09 October 2013 - 12:09 AM said:

so how would i go about doing that, using a regEx to see if i can find the arguments i need before i try and pass it through textutils.unserialize?

That's probably the best way to do it. I'd just turn this:

				local isTable = textutils.unserialize(bfD)
				if type(isTable) == "table" and isTable["ptl"] and isTable["cid"] then
				  pkg["data"] = isTable
				  pkg["key"] = keys[i]
				  pkg["pwd"] = pass[I]
				end

… to this:

				if string.sub(bfD,1,1) == "{" and string.sub(bfD,#bfD,#bfD) == "}" then
				  local isTable = textutils.unserialize(bfD)
				  if type(isTable) == "table" and isTable["ptl"] and isTable["cid"] then
					pkg["data"] = isTable
					pkg["key"] = keys[i]
					pkg["pwd"] = pass[I]
				  end
				end