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Author: SABERGLOW

Week 4/1. Known Language and Key Length/CaesarCipher.java

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+import edu.duke.*;
+
+public class CaesarCipher {
+    private String alphabet;
+    private String shiftedAlphabet;
+    private int theKey;
+    
+    public CaesarCipher(int key) {
+        theKey = key;
+        alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
+        shiftedAlphabet = alphabet.substring(key) +
+                            alphabet.substring(0,key);
+        alphabet = alphabet + alphabet.toLowerCase();
+        shiftedAlphabet = shiftedAlphabet + shiftedAlphabet.toLowerCase();
+    }
+    
+    private char transformLetter(char c, String from, String to) {
+        int idx = from.indexOf(c);
+        if (idx != -1) {
+            return to.charAt(idx);
+        }
+        return c;
+    }
+    
+    public char encryptLetter(char c) {
+        return transformLetter(c, alphabet, shiftedAlphabet);
+    }
+    
+    public char decryptLetter(char c) {
+        return transformLetter(c, shiftedAlphabet, alphabet);
+    }
+    
+    private String transform(String input, String from, String to){
+        StringBuilder sb = new StringBuilder(input);
+        for (int i = 0; i < sb.length(); i++) {
+            char c = sb.charAt(i);
+            c = transformLetter(c, from, to);
+            sb.setCharAt(i, c);
+        }
+        return sb.toString();
+    }
+    
+    public String encrypt(String input) {
+        return transform(input, alphabet, shiftedAlphabet);
+    }
+    
+    public String decrypt(String input) {
+        return transform(input, shiftedAlphabet, alphabet);
+    }
+    
+    public String toString() {
+        return "" + theKey;
+    }
+    
+}

Week 4/1. Known Language and Key Length/CaesarCracker.java

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+import edu.duke.*;
+
+public class CaesarCracker {
+    char mostCommon;
+    
+    public CaesarCracker() {
+        mostCommon = 'e';
+    }
+    
+    public CaesarCracker(char c) {
+        mostCommon = c;
+    }
+    
+    public int[] countLetters(String message){
+        String alph = "abcdefghijklmnopqrstuvwxyz";
+        int[] counts = new int[26];
+        for(int k=0; k < message.length(); k++){
+            int dex = alph.indexOf(Character.toLowerCase(message.charAt(k)));
+            if (dex != -1){
+                counts[dex] += 1;
+            }
+        }
+        return counts;
+    }
+    
+    public int maxIndex(int[] vals){
+        int maxDex = 0;
+        for(int k=0; k < vals.length; k++){
+            if (vals[k] > vals[maxDex]){
+                maxDex = k;
+            }
+        }
+        return maxDex;
+    }
+
+    public int getKey(String encrypted){
+        int[] freqs = countLetters(encrypted);
+        int maxDex = maxIndex(freqs);
+        int mostCommonPos = mostCommon - 'a';
+        int dkey = maxDex - mostCommonPos;
+        if (maxDex < mostCommonPos) {
+            dkey = 26 - (mostCommonPos-maxDex);
+        }
+        return dkey;
+    }
+    
+    public String decrypt(String encrypted){
+        int key = getKey(encrypted);
+        CaesarCipher cc = new CaesarCipher(key);
+        return cc.decrypt(encrypted);
+        
+    }
+}

Week 4/1. Known Language and Key Length/VigenereBreaker.java

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+import java.util.*;
+import edu.duke.*;
+
+public class VigenereBreaker
+{
+    public String sliceString(String message, int whichSlice, int totalSlices)
+    {
+        StringBuilder result = new StringBuilder();
+        for(int i=whichSlice; i<message.length(); i+=totalSlices)
+        {
+            result.append(message.charAt(i));
+        }
+        return result.toString();
+    }
+
+    public int[] tryKeyLength(String encrypted, int klength, char mostCommon)
+    {
+        CaesarCracker CC = new CaesarCracker(mostCommon);
+        int[] key = new int[klength];
+        for(int i=0; i<klength; i++)
+        {
+            String slice = sliceString(encrypted, i, klength);
+            int resKey = CC.getKey(slice);
+            System.out.println("KEY: " + resKey);
+            key[i] = resKey;
+        }
+
+        return key;
+    }
+
+    public void breakVigenere ()
+    {
+        FileResource fr = new FileResource();
+        String FILE = fr.asString();
+        int[]key = tryKeyLength(FILE, 4, 'e');
+        VigenereCipher VC = new VigenereCipher(key);
+        String decrypt = VC.decrypt(FILE);
+        System.out.println("DECRYPTED MESSAGE: " + decrypt);
+    }
+
+    ///////////////////////////////////////////////////////////
+    public static void main (String []args)
+    {
+        VigenereBreaker VC = new VigenereBreaker();
+        VC.breakVigenere();
+    }
+    
+}

Week 4/1. Known Language and Key Length/VigenereCipher.java

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+import edu.duke.*;
+import java.util.*;
+
+public class VigenereCipher {
+    CaesarCipher[] ciphers;
+    
+    public VigenereCipher(int[] key) {
+        ciphers = new CaesarCipher[key.length];
+        for (int i = 0; i < key.length; i++) {
+            ciphers[i] = new CaesarCipher(key[i]);
+        }
+    }
+    
+    public String encrypt(String input) {
+        StringBuilder answer = new StringBuilder();
+        int i = 0;
+        for (char c : input.toCharArray()) {
+            int cipherIndex = i % ciphers.length;
+            CaesarCipher thisCipher = ciphers[cipherIndex];
+            answer.append(thisCipher.encryptLetter(c));
+            i++;
+        }
+        return answer.toString();
+    }
+    
+    public String decrypt(String input) {
+        StringBuilder answer = new StringBuilder();
+        int i = 0;
+        for (char c : input.toCharArray()) {
+            int cipherIndex = i % ciphers.length;
+            CaesarCipher thisCipher = ciphers[cipherIndex];
+            answer.append(thisCipher.decryptLetter(c));
+            i++;
+        }
+        return answer.toString();
+    }
+    
+    public String toString() {
+        return Arrays.toString(ciphers);
+    }
+    
+}