Cryptography

Starting Code: import java.util.Scanner; /** * Simple Polyalphabetic Cryptography * * @Chris Thiel * @28 Feb 2009 */ public class VignereCipherStartingCode { private static final String alphabet="ABCDEFGHIJKLMNOPQRSTUVWXYZ"; private static int nextChar(String k, int i){ i=i%k.length(); String letter=k.substring(i,i+1); return alphabet.indexOf(letter); } public static String encode (String m, String k){ String result=""; for (int i=0; i<m.length(); i++){ int offset=nextChar(k, i); String letter = m.substring(i,i+1); int newLetterIndex= alphabet.indexOf(letter)+offset; newLetterIndex=newLetterIndex % 26; result+=alphabet.substring( newLetterIndex, newLetterIndex+1); } return result; } public static String decode (String m, String k){ String result=""; return result; } public static void main(String[] args) { Scanner kb=new Scanner(System.in); System.out.print("Type a key: "); String key=kb.nextLine(); key=key.toUpperCase(); key=key.replace(" ","");//omit spaces System.out.print("Type a message: "); String message=kb.nextLine(); message=message.toUpperCase(); message=message.replace(" ",""); System.out.println("Using the key \""+key+"\" on \""+message+"\":"); String codedMessage=encode(message,key); System.out.println("Coded="+codedMessage); System.out.println("Decoded="+decode(codedMessage,key)); System.out.println("Using the key 'LOVE' we encode 'BOOHOO' we should get 'MCJLZC' : "+encode("BOOHOO","LOVE")); System.out.println("Using the key 'QUICK' we decode 'TOKMXEQ' we should get 'DUCKNOW': "+decode("TOKMXEQ","QUICK")); } } 8 points: Complete the decode method so it can decipher the Vignere Cipher 9 points: Adapt this so it can do a Progressive Polyalphabetic Cipher rather than a key 10 points: Adapt the CarTalk Employee Applet's graphic user interface so that you can type a message in one text area, press a button and it shows the encoded text (using the Progressive Cipher), press another button and it shows the decoded text. 11 points: Add a "key field" to the Applet, and use the Vignere Cipher, working in a similiar fashion as the 10 point version

An episode of the APCS Java podcast, hosted by Chris Thiel, titled "Cryptography" was published on February 28, 2009.

February 28, 2009 · APCS Java

Summary

Starting Code: import java.util.Scanner; /** * Simple Polyalphabetic Cryptography * * @Chris Thiel * @28 Feb 2009 */ public class VignereCipherStartingCode { private static final String alphabet="ABCDEFGHIJKLMNOPQRSTUVWXYZ"; private static int nextChar(String k, int i){ i=i%k.length(); String letter=k.substring(i,i+1); return alphabet.indexOf(letter); } public static String encode (String m, String k){ String result=""; for (int i=0; i<m.length(); i++){ int offset=nextChar(k, i); String letter = m.substring(i,i+1); int newLetterIndex= alphabet.indexOf(letter)+offset; newLetterIndex=newLetterIndex % 26; result+=alphabet.substring( newLetterIndex, newLetterIndex+1); } return result; } public static String decode (String m, String k){ String result=""; return result; } public static void main(String[] args) { Scanner kb=new Scanner(System.in); System.out.print("Type a key: "); String key=kb.nextLine(); key=key.toUpperCase(); key=key.replace(" ","");//omit spaces System.out.print("Type a message: "); String message=kb.nextLine(); message=message.toUpperCase(); message=message.replace(" ",""); System.out.println("Using the key \""+key+"\" on \""+message+"\":"); String codedMessage=encode(message,key); System.out.println("Coded="+codedMessage); System.out.println("Decoded="+decode(codedMessage,key)); System.out.println("Using the key 'LOVE' we encode 'BOOHOO' we should get 'MCJLZC' : "+encode("BOOHOO","LOVE")); System.out.println("Using the key 'QUICK' we decode 'TOKMXEQ' we should get 'DUCKNOW': "+decode("TOKMXEQ","QUICK")); } } 8 points: Complete the decode method so it can decipher the Vignere Cipher 9 points: Adapt this so it can do a Progressive Polyalphabetic Cipher rather than a key 10 points: Adapt the CarTalk Employee Applet's graphic user interface so that you can type a message in one text area, press a button and it shows the encoded text (using the Progressive Cipher), press another button and it shows the decoded text. 11 points: Add a "key field" to the Applet, and use the Vignere Cipher, working in a similiar fashion as the 10 point version

Episode Description

Starting Code:

import java.util.Scanner;
/**
 * Simple Polyalphabetic Cryptography
 * 
 * @Chris Thiel 
 * @28 Feb 2009
 */
public class VignereCipherStartingCode
{
    private static final String alphabet="ABCDEFGHIJKLMNOPQRSTUVWXYZ";
    private static int nextChar(String k, int i){
        i=i%k.length();
        String letter=k.substring(i,i+1);
        return alphabet.indexOf(letter);
    }
    public static String encode (String m, String k){
        String result="";
        for (int i=0; i<m.length(); i++){
            int offset=nextChar(k, i);
            String letter = m.substring(i,i+1);
            int newLetterIndex= alphabet.indexOf(letter)+offset;
            newLetterIndex=newLetterIndex % 26;
            result+=alphabet.substring( newLetterIndex, newLetterIndex+1);
        }
        return result;
    }
    public static String decode (String m, String k){
        String result="";   
        return result;
    }
    public static void main(String[] args)
    {
        Scanner kb=new Scanner(System.in);
        System.out.print("Type a key: ");
        String key=kb.nextLine();
        key=key.toUpperCase();
        key=key.replace(" ","");//omit spaces
        System.out.print("Type a message: ");
        String message=kb.nextLine();
        message=message.toUpperCase();
        message=message.replace(" ","");
        System.out.println("Using the key \""+key+"\" on \""+message+"\":");
        String codedMessage=encode(message,key);
        System.out.println("Coded="+codedMessage);
        System.out.println("Decoded="+decode(codedMessage,key));
        System.out.println("Using the key 'LOVE' we encode 'BOOHOO' we should get 'MCJLZC' : "+encode("BOOHOO","LOVE"));
        System.out.println("Using the key 'QUICK' we decode 'TOKMXEQ' we should get 'DUCKNOW': "+decode("TOKMXEQ","QUICK"));
  
    }
}

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• 8 points: Complete the decode method so it can decipher the Vignere Cipher
  
• 9 points: Adapt this so it can do a Progressive Polyalphabetic Cipher rather than a key
  
• 10 points: Adapt the CarTalk Employee Applet's graphic user interface so that you can type a message in one text area, press a button and it shows the encoded text (using the Progressive Cipher), press another button and it shows the decoded text.
  
• 11 points: Add a "key field" to the Applet, and use the Vignere Cipher, working in a similiar fashion as the 10 point version