Password File Creator (hashing and Salting)

--[[
-- Program: MkUser
-- Version: 0.1
-- Author:  LebaLusch
-- Created: 19/11/16 -uk date style
-- Dependencies:
api=sha sha256.lua made by MaHuJa  https://github.com/MaHuJa/CC-scripts/blob/master/sha256.lua (From http://pastebin.com/gsFrNjbt)
-- Use: This will Check a password file (if not Present it will create it) for a user Name if not present it will store the name and Password.  The password will be Hashed and Salted.
-- Features i want to add:
  Removal of users.
  Auto Add a Admin user.

-- Credits:
All those that have Created and contributed to making Lua what it is today.
This is my variation of CompuTech's user maker Whos code can be found at page (How to Securely Store Passwords).
This can be found at http://www.computercraft.info/forums2/index.php?/topic/27496-how-to-securely-store-passwords/page__p__260768#entry260768
--Links:
http://www.lua.org/
http://www.computercraft.info/
http://www.computercraft.info/forum2
http://www.minecraft.net
]]
--[[Licence]]
--[[
THE SOFTWARE IS PROVIDED "AS IS",
WITHOUT WARRANTY OF ANY KIND,
EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE PROGRAM
IS WITH YOU.  SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF
ALL NECESSARY SERVICING, REPAIR OR CORRECTION.
YOU MAY NOT USE ANY PART OF THIS SOFTWARE UNLESS YOU CREDIT THE AUTHOR FOUND ABOVE IN YOUR HEADER.
YOU MAY NOT USE ANY PART OF THIS SOFTWARE IN A COMERCIAL PRODUCT FOR PROFIT,
OR SOFTWARE THAT DOES NOT ALLOW THE USER FULL ACCESS TO THE CODE.
]]

--Api's to load
os.loadAPI("sha")
local fileName = "PSW" --name of password file.
--FUNCTIONS

  local function setScreen()-- works, This clears the screen and positions us in the top left of the terminal. This needs to be a global function.
   term.clear() -- set screen up
   term.setCursorPos(1,1)
   term.setCursorBlink(true)  
  end--close function

  local function createFile ( )--This creates The password file if it doesnt exsit.
   setScreen()
   write(">Creating User-\n\n")
   if not fs.exists(fileName) then --Create a password file
	
	local f = fs.open(fileName, "w")  --This creates the file in a writable state as a veriableM
	  f.write(textutils.serialize({ })) --This puts the text we want in the file
	  f.close() --This closes the file
  
   else
	--nothing
   end
  end

  local function readFile()
   local f = fs.open(fileName,"r")
   local usrs = textutils.unserialize(f.readAll())
   f.close()-- we have now checked the file to see whos in it read and stored all the names and passwords in memorry.  
  end


   function userName()
   setScreen()
   write(">Creating User-\n\n")
   write(">User Name: ") -- ask for username
   local u = read()--read the user name response, comit to variable u
  
   local f = fs.open(fileName,"r")
   local usrs = textutils.unserialize(f.readAll())
   f.close()
  
   if not usrs [u] then -- we reconise its a new user and carry on and create the password .usrs
  
  
	write(">Password: ") --ask for user password
	 p = read("*")--read the user password response, comit to variable p
	write(">Password: ") --ask for user password again and check them agains each other
   local chkP = read("*")

   if p == chkP then
	write("\n>Passwords Match\n")
	os.sleep(3)

   else
	write(">Passwords Do Not Match\n")
	os.sleep(3)
	userName()
   end

  
	local salt = os.time() *math.random(1,10000000000000)*math.random(1,10000000000000)
	*math.random (1,10000000000000) -- massive over kill to get a really big random number i know
  
	usrs[u] = {
		   pwd = sha.sha256( p .. salt ),
		   salt = salt,
	  }
	  local f = fs.open(fileName, "w")
	  f.write( textutils.serialize( usrs ) )
	  f.close()
  
  
	write(">User created\n")
	os.sleep(3)
	setScreen()
   else
	setScreen()
	write(">User Name already taken\n")
	write(">Please Try again")
	os.sleep(3)
	userName()
   end
  end
--END OF FUNCTIONS
--CODE

createFile(fileName) --call function and pass file name  PSW into it.
readFile(fileName) -- Read the File PSW
userName() -- take the user name and check it and also check the password with each other.
write("\n\n--program finished--\n") --place card holder
-- END OF CODE