Virtual Enigma Machine Implementation

After watching a video on numberphile thought it would be interesting to implement a virtual version on the Enigma cipher machine.

Step 1: Install Scala and Eclipse IDE for Scala.

http://www.scala-lang.org/downloads, http://scala-ide.org/

Step 2: Review the numberphile video and how the Enigma machine works

Step 3: Implement each function of the machine

1. Rotors
   • Rotor choices, rotors have different circuitry (0-24) – static value for each message
   • Initial rotor combination (0-25) – static value for each message
   • Rotor increment – Faster rotor, middle rotor, slow rotor
2. Plug board
   • 10 wires
   • swapping 2 letters
   • static value for each message

Step 4: Write an interface between the functions and a basic interface (text?)

Step 5: Test!

Conclusion: Using Scala (trying anyway) the implementation is not very complex. What is more difficult is replicating the original machines where the output character could not equal the input character. The limitation Turing used to crack the machines. Might see if I can implement that later then test out the cracking method. Not sure how easy it would be to break the current implementation…

CODE (EnigmaMachine.scala, EnigmaMachine.class):

// Virtual reconstruction of what the enigma machines did
// The replication is of the improved version where the input could result in the same output

object EnigmaMachine {
//////////////// ENCRYPTION/DECRYPTION FUNCTIONS \\\\\\\\\\\\\\\\\\\\\
    //to replicate the simple machine circuit chars are converter to 0 - 25
    def convertMessageToSimpleInt(rawInput: String):List[Int] = {
        val userMessage = rawInput.toUpperCase
      (for (x <- userMessage) yield if (x != 32) (x.toInt - 65) else 26).toList
    }
    
    //for all integers in the list, convert
    def convertMessageToString(input: List[Int]): String = {
      (for (x <- input) yield if (x == 26) " " else (x + 65).toChar).mkString
    } 
    
    def enigmaGo(rotorChoices: List[Int], rotorPositions: List[Int], inputMessage: List[Int], encrypt: Boolean): List[Int] = {    
      // incrementing the rotors is dont based on the number of previous chars.. instead of the previous position
      def incrementRots(nth: Int): List[Int] = {
        val rot0 = (rotorPositions(0) + nth) % 26 //fast rotor
        val rot1 = (rotorPositions(1) + (nth / 26)) % 26 //medium rotor
        val rot2 = (rotorPositions(2) + ((nth / 26) /26)) % 26 //slow rotor
        List(rot0, rot1, rot2)
      }
      //applies the rotor encryption then the scramble board
      def transmuteElement(element: Int, rotPosApp: List[Int]): Int = {
        val rotorTotal = rotorList(rotorChoices(0))(rotPosApp(0)) +
              rotorList(rotorChoices(1))(rotPosApp(1)) +
              rotorList(rotorChoices(2))(rotPosApp(2)) 
        
      def scramble(inputVal:Int):Int = plugMap1.find(x => (x._1 == inputVal) || (x._2 == inputVal)) match {
            case Some(y) => if (y._1 == inputVal) y._2 else y._1 
          case None => inputVal
      }
        if (element == 26) element
        else if (encrypt) (scramble(element) + rotorTotal) % 26 else { 
            //decrypt is a bit messy atm :( 
            if (element - (rotorTotal % 26) < 0) scramble(element - (rotorTotal % 26) + 26) else scramble(element - (rotorTotal % 26))
          }     
      }
      
      //Accumulator hold the input and output lists, when input list is empty, return output.. also tail recursive
      def enigmaAccu(remInput: List[Int], rotPos: List[Int], accumOutput: List[Int]): List[Int] = {
              if (remInput.isEmpty) accumOutput
            else enigmaAccu(remInput.tail, incrementRots(accumOutput.length), accumOutput:+(transmuteElement(remInput.head, rotPos)))
      }
      
      enigmaAccu(inputMessage, rotorPositions, Nil) //start the process
    }
////////////////////   \\\\\\\\\\\\\\\\\\\\\\\\\
    
//////////////// UI STUFF \\\\\\\\\\\\\\\\\\\\\
    def useMachine(rotorChoices: List[Int], rotorStartVals: List[Int], activity: String) = {
            spamLine
            val inputMessage = convertMessageToSimpleInt(askInput("Please enter a message to be " + activity + ", use only a-z: "))
            val resultingMessage = enigmaGo(rotorChoices, rotorStartVals, inputMessage, if (activity == "encrypted") true else false)
            spamLine
            println("Your message has been " + activity + ": ")
        println(convertMessageToString(resultingMessage))
            spamLine
            exit(0)
    }

    def getRotorChoices(s1:String, p: String => Boolean):List[Int] = {
        val slot0 = getUserInput(s1 + "fast slot: ", "Entry Invalid.", p).mkString
        val slot1 = getUserInput(s1 + "medium slot: ", "Entry Invalid.", p).mkString
        val slot2 = getUserInput(s1 + "slow slot: ", "Entry Invalid.", p).mkString
        List(slot0.toInt,slot1.toInt,slot2.toInt)
    }
    
    def spamLine = println("##############################################")
    
    def askInput(statement: String) = { 
      val input = readLine(statement)
      if (input == "") "99" else input
    }
    
    def askAgain(statement: String, f: => String) = {
        println(statement)
        f
    } 
    
    def inputVals(f1: => String, f2: => String) = Stream.cons( f1, Stream.continually(f2))
    
    def getUserInput(s1: String, s2: String, p:String => Boolean) = inputVals(askInput(s1), askAgain(s2, askInput(s1))).find(p)
////////////////////   \\\\\\\\\\\\\\\\\\\\\\\\\
    
//////////////// MAIN \\\\\\\\\\\\\\\\\\\\\ 
        def main(args: Array[String]) {
            println("### WELCOME TO THE ENIGMA MACHINE! ###" )
            // GET INITIAL MACHINE SETTINGS FROM USER 
            // ROTOR PLACEMENT CONFIG
            val rotorChoices = getRotorChoices("Choose rotor (0 - 4) for ", x => (x.toInt >= 0 && x.toInt < 5)) 
            // ROTOR START VALS 
            val rotorStartVals =  getRotorChoices("Choose rotor START VAL (0 - 25) for ", x => (x.toInt >= 0 && x.toInt < 25))
            // PLUG MAP
            println("There is only 1 plug map option at present:") 
            println(plugMap1.toString.drop(4))
            //ENCRYPT OF DECRYPT - ONLY RELEVENT FOR GUI TEXT.. bleh not quite need to reverse circuit manually
            val userChoice = getUserInput("Press 1 to encrypt, 2 to decrypt: ", "Entry Invalid.", x => (x == "2" || x == "1"))
            userChoice.mkString match {
              case "1" => useMachine(rotorChoices, rotorStartVals, "encrypted") 
              case "2" => useMachine(rotorChoices, rotorStartVals, "decrypted")
              case default => exit(0)
            }
    }
////////////////////   \\\\\\\\\\\\\\\\\\\\\\\\\

//////////////// CONSTANTS \\\\\\\\\\\\\\\\\\\\\
    val rotorList = List(List(6, 17, 4, 3, 23, 22, 21, 5, 0, 19, 20, 11, 16, 9, 13, 24, 18, 1, 8, 2, 7, 10, 12, 14, 25, 15)
    ,List(2, 7, 23, 12, 13, 15, 18, 1, 8, 11, 0, 3, 10, 5, 24, 4, 17, 19, 6, 9, 20, 14, 25, 21, 16, 22)
    ,List(23, 1, 19, 18, 0, 10, 3, 8, 9, 21, 2, 12, 13, 14, 24, 6, 20, 16, 11, 17, 15, 7, 4, 25, 22, 5)
    ,List(21, 22, 16, 2, 18, 20, 15, 9, 5, 1, 17, 10, 3, 6, 0, 13, 11, 23, 4, 12, 19, 8, 7, 25, 24, 14)
    ,List(25, 3, 11, 7, 5, 15, 24, 10, 21, 6, 12, 17, 8, 23, 2, 18, 19, 14, 4, 0, 20, 9, 22, 1, 16, 13))
    
    val plugMap1 = List((3,7),(11,16),(18,24),(17,9),(21,19),(14,13),(0,12),(1,25),(22,20),(4,6))
////////////////////   \\\\\\\\\\\\\\\\\\\\\\\\\
}