Hello all! I have a very hard assignment for CSC 143 that I have been trying to
ID: 653034 • Letter: H
Question
Hello all! I have a very hard assignment for CSC 143 that I have been trying to figure out for days and now I need help. The following is a copy of the assignment. The part in bold is where the actual assignment requirments begin.
This assignment was borrowed by my professor from a previous course, so I am sure that some folks out there have managed to solve it.
Thanks in advance for your help.
Substitution ciphers that encode a message by substituting one character for another go back at least as far as Julius Caesar, who used a rotating character scheme to encode military orders. This simple type of encryption is vulnerable to statistical attacks, however, as anyone who has solved CRYPTOGRAM puzzles can attest. In World War II, the Nazi military employed an encryption scheme that addressed this weakness of simple substitution ciphers. This scheme, implemented by typewriter-sized devices known as Enigma machines, gave the Nazis a tactical advantage that greatly contributed to their early success in the war. In fact, the eventual breaking of this coding scheme by researchers at Bletchley Park, England (including Alan Turing) is hailed as one of the turning points of the war.
Enigma machines used interchangeable rotors that could be placed in different orientations to obtain different substitution patterns. More significantly, the rotors rotated after each character was encoded, changing the substitution pattern and making the code very difficult to break. The behavior of the rotating rotors can be modeled, in a simplified form, by a device consisting of labeled, concentric rings. For example, the model below has three rings labeled with the letters of the alphabet and '#' (representing a space).
To encrypt a character using this model, find the character on the inner rotor (i.e., the inside ring) and note the character aligned with it on the outer rotor (i.e., the outside ring), then find that character on the middle rotor (i.e., the middle ring) and output the one aligned with it on the outer rotor. After a character is encrypted, turn the inner rotor clockwise one step. Whenever the inner rotor returns to its original orientation, the middle rotor turns once in lock-step, just like the odometer in a car.
For example, in this configuration the character 'A' would be encrypted as 'N', since 'A' on the inner rotor is aligned with 'H' on the outer rotor, and 'H' on the middle rotor is aligned with 'N' on the outer rotor. After performing this encryption, the inner rotor is rotated clockwise, so the letter 'A' would next be encrypted as 'D'.
Note that decrypting a message requires following the same steps, only in reverse (i.e., find the character on the outer rotor, note the character aligned with it on the middle rotor, find that character on the outer rotor, then output the character aligned with it on the inner rotor).
For this assignment, you are to design a Java class named Enigma that simulates this three-ring model. You may assume that all Enigma models have the same outer rotor, as shown in the above diagram. That is, the outer rotor consists of the 26 capital letters and the '#' symbol (representing a space) in the following clockwise order: #BDFHJLNPRTVXZACEGIKMOQSUWY. Since the other rotors are interchangeable, however, their contents and alignment relative to the outer rotor must be specified when constructing an Enigma model. For example, the initial settings of the inner and middle rotors in the above diagram are #GNUAHOVBIPWCJQXDKRYELSZFMT and #EJOTYCHMRWAFKPUZDINSXBGLQV, respectively. Using an Enigma object, it should be possible to encode and decode text messages, with the appropriate rotation of the rotors occurring after each character encoding/decoding.
You should also design and implement a client program that makes it simple for the user to specify the rotor settings on an Enigma model, and encode or decode text. Once you have your model working, test it by decoding the message OKNNWRDHGERPILRLAMFZF#FMUC using the diagram settings.
Note: if you would like to make your own 3-ring Enigma model out of paper, download this online form, cut out the rings, and follow the instructions at the site.
Design and implementation guidelines:
- Javadoc comment all class files and methods
- Use validation and generate and handle exceptions as appropriate
-Structured code - use methods to eliminate redundancy and break large methods into smaller, logical subproblems
Explanation / Answer
#include<iostream.h>
public class Enigma
{
private String inn;
private String mid;
private String innR;
private String midR;
private String outR;
enum Ring {INNER, MIDDLE, OUTER};
public Enigma(){
inn = "#GNUAHOVBIPWCJQXDKRYELSZFMT";
mid = "#EJOTYCHMRWAFKPUZDINSXBGLQV";
outR = "#BDFHJLNPRTVXZACEGIKMOQSUWY";
resetEnigma();
}
/**
* Sets the code for Inner rotor. Code should start with # and must contain all
* characters form A-Z in any order.
* @param code The code to set.
* @throws InvalidCharException
*/
public void setRing (Ring r, String code) throws InvalidCharException{
code = code.toUpperCase();
if( isValid(code) ){
switch( r ){
case INNER : inn = code; break;
case MIDDLE : mid = code; break;
case OUTER : outR = code; break;
}
resetEnigma();
}
else
throw new InvalidCharException("Code should start with # and should"
+ " contain each of A-Z in any order.");
}
public final void resetEnigma(){
innR = inn.substring(0);
midR = mid.substring(0);
}
/**
* Encodes the @src string. If any illegal character is found an exception is thrown
* @param src The string to be encoded.
* @return Encoded string
* @throws InvalidCharException
*/
public String encodeString(String src) throws InvalidCharException{
char [] encodedChars = new char[src.length()];
src = src.toUpperCase();
resetEnigma();
for( int i=0; i<src.length(); i++){
char ch = src.charAt(i);
ch = ch==' ' ? '#' : ch; //replace <space> by '#'
if( ch =='#' || (ch>='A' && ch<='Z') ){
int indInner = innR.indexOf(ch);
char outChar = outR.charAt(indInner);
int indMiddle = midR.indexOf(outChar);
encodedChars[i] = outR.charAt(indMiddle);
rotateEnigma();
} else {
throw new InvalidCharException("Invalid Character in source string.");
}
}
return new String(encodedChars);
}
/**
* Decodes the @src string. If any illegal character is found an Exception is thrown
* @param src The string to be decoded
* @return Decoded string
* @throws InvalidCharException
*/
public String decodeString(String src) throws InvalidCharException{
char [] decodedChars = new char[ src.length()];
src = src.toUpperCase();
resetEnigma();
for( int i=0; i<src.length(); i++){
char ch = src.charAt(i);
if( ch =='#' || (ch>='A' && ch<='Z') ){
int indOuter = outR.indexOf(ch);
char midChar = midR.charAt(indOuter);
int indOuter2 = outR.indexOf(midChar);
decodedChars[i] = innR.charAt(indOuter2);
if( decodedChars[i] == '#')
decodedChars[i] = ' ';
rotateEnigma();
} else {
throw new InvalidCharException("Invalid Character in source string");
}
}
return new String(decodedChars);
}
/**
* Function to check if the code is valid cipher code. A valid cipher code starts with a '#'
* contains all characters from 'A-Z' in any order
* @param src the string to be checked for validity
* @return return true if condition is satisfied
* @throws InvalidCharException if the illegal character other than 'A-Z' or '#' is found
*/
public boolean isValid(String code){
if( code.indexOf('#') != 0 || code.length() != 27 )
return false;
for( char i='A'; i<='Z'; i++)
if( code.indexOf(i) == -1)
return false;
return true;
}
public void printCodes(){
System.out.println("The current codes are : ");
System.out.println("Outer Ring : " + outR);
System.out.println("Middle Ring: " + mid);
System.out.println("Inner Ring : " + inn);
}
private void rotateMidR(){
int l = midR.length();
midR = midR.substring(l-1, l) + midR.substring(0, l-1) ;
}
private void rotateEnigma(){
int l = innR.length();
innR = innR.substring(l-1, l) + innR.substring(0, l-1) ;
if( innR.equals(inn) )
rotateMidR();
}
/*
* Exception to handle invalid characters the code.
*/
@SuppressWarnings("serial")
class InvalidCharException extends Exception{
String msg;
InvalidCharException(){
msg = "Invalid Character found.";
}
InvalidCharException( String msg){
this.msg = msg;
}
@Override
public String toString(){
return msg;
}
}
}
//CLIENTCLASS
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
public class EnigmaClient
{
public static void main(String [] argv
{
String encoded = "OKNNWRDHGERPILRLAMFZF#FMUC";
boolean exitLoop = false;
Enigma em = new Enigma();
try
{
System.out.println("Deocded string of " + encoded + " is " + em.decodeString(encoded) );
}
catch (Enigma.InvalidCharException ex)
{
ex.toString();
}
while( !exitLoop )
{
try
{
BufferedReader bufferRead = new BufferedReader(new InputStreamReader(System.in));
System.out.println("____ Menu ____ ");
System.out.println("v - View the Codes");
System.out.println("i - set the inner ring Code");
System.out.println("m - set the middle ring Code");
System.out.println("o - set the outer ring Code");
System.out.println("e - Encode a string");
System.out.println("d - Decode a cipher text");
System.out.println("t - test both encoding and decoding");
System.out.println("q - quit");
System.out.println("String will be converted to UPPER case by the program.");
System.out.println("Your Choice : ");
String s = bufferRead.readLine();
if( s.length()==0 ) continue;
switch( s.charAt(0)){
case 'v':
em.printCodes();
break;
case 'i':
case 'm':
case 'o':
System.out.println("Enter the cipher code (Should start with #): ");
System.out.println("String will be converted to UPPER case by the program.");
String code=bufferRead.readLine();
switch( s.charAt(0)){
case 'i': em.setRing(Enigma.Ring.INNER, code); break;
case 'm': em.setRing(Enigma.Ring.MIDDLE, code); break;
case 'o': em.setRing(Enigma.Ring.OUTER, code); break;
}
em.printCodes();
break;
case 'e':
System.out.println("Enter the plain text: ");
String src=bufferRead.readLine();
System.out.println("Encoded string is " + em.encodeString(src) );
break;
case 'd':
System.out.println("Enter the cipher text: ");
src=bufferRead.readLine();
System.out.println("Decoded string is " + em.decodeString(src) );
break;
case 't':
System.out.println("Enter the plain text which will encoded and decoded: ");
src=bufferRead.readLine();
String cipher = em.encodeString(src);
System.out.println("Encoded string is " + cipher );
System.out.println("Decoded string is " + em.decodeString(cipher) );
break;
case 'q':
exitLoop = true;
break;
default:
System.out.println("Invalid Input");
break;
}
System.out.println(s);
} catch(IOException e)
{
e.printStackTrace();
} catch ( Enigma.InvalidCharException ex){
System.out.println( ex + "Operation Failed");
}
}
}
}
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