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  1. import java.util.*;
  2.  
  3. public class Main {
  4.     public static void main(String[] args) {
  5.         int[] ciphertext = {
  6.             102, 141, 142, 161, 148, 131, 158, 157, 120, 131, 
  7.             126, 153, 130, 143, 154, 135, 118, 137, 148, 111, 
  8.             116, 145, 134, 133, 118, 103, 136, 107, 138, 127, 
  9.             102, 131, 194, 99, 114, 200, 202, 127, 120, 105, 
  10.             126, 202, 108, 194, 198, 214, 222, 204, 116, 224, 
  11.             194, 198, 202, 230, 166, 222, 216, 234, 232, 210, 
  12.             222, 220, 210, 230, 194, 230, 198, 210, 210, 230, 
  13.             234, 218, 222, 204, 194, 216, 216, 224, 216, 194, 
  14.             210, 220, 232, 202, 240, 232, 198, 208, 194, 228, 230
  15.         };
  16.  
  17.         List<String> possibleSolutions = decryptAll(ciphertext);
  18.  
  19.         System.out.println("\nTop possible solutions:");
  20.         for (String solution : possibleSolutions) {
  21.             System.out.println(solution);
  22.         }
  23.     }
  24.  
  25.     public static List<String> decryptAll(int[] ct) {
  26.         int length = ct.length;
  27.         List<String> solutions = new ArrayList<>();
  28.         Map<Integer, String> keyToText = new HashMap<>();
  29.  
  30.         System.out.println("Testing all possible keys...");
  31.  
  32.         for (int initialKey = length/2; initialKey <= length; initialKey++) {
  33.             StringBuilder plaintext = new StringBuilder();
  34.             boolean valid = true;
  35.             int currentKey = initialKey;
  36.  
  37.             for (int encrypted : ct) {
  38.                 boolean found = false;
  39.                 // Try all ASCII characters (0-255)
  40.                 for (int c = 0; c <= 255; c++) {
  41.                     if (c + (c % currentKey) == encrypted) {
  42.                         plaintext.append((char)c);
  43.                         found = true;
  44.                         break;
  45.                     }
  46.                 }
  47.  
  48.                 if (!found) {
  49.                     valid = false;
  50.                     break;
  51.                 }
  52.  
  53.                 currentKey++;
  54.             }
  55.  
  56.             if (valid) {
  57.                 String solution = plaintext.toString();
  58.                 solutions.add(solution);
  59.                 keyToText.put(initialKey, solution);
  60.             }
  61.         }
  62.  
  63.         // Score solutions by English-like characteristics
  64.         solutions.sort((a, b) -> {
  65.             int scoreA = englishScore(a);
  66.             int scoreB = englishScore(b);
  67.             return Integer.compare(scoreB, scoreA);
  68.         });
  69.  
  70.         return solutions.subList(0, Math.min(5, solutions.size()));
  71.     }
  72.  
  73.     private static int englishScore(String text) {
  74.         int score = 0;
  75.         String commonLetters = "etaoinshrdlu ETAOINSHRDLU";
  76.  
  77.         for (char c : text.toCharArray()) {
  78.             if (commonLetters.indexOf(c) >= 0) score += 2;
  79.             else if (c >= 32 && c <= 126) score += 1;
  80.             if (Character.isLetterOrDigit(c) )score += 1;
  81.         }
  82.  
  83.         return score;
  84.     }
  85. }
Success #stdin #stdout 0.18s 55868KB
comments (?)
stdin 
Standard input is empty
stdout 
Testing all possible keys...

Top possible solutions:
3hismess<g?sAoMl;nJb:tCo;aDdEo3rac9des<i?e6ackof:pacesSolutionisasciisumofallplaintextchars
3ghrldrr<f?rAnMk;mJa:sCn;`DcEn3q‘b9Ǘr<h?e6ack¦f:pacesSolutionisasciisumofallplaintextchars
3fgqkcqq<e?qAmsj;lJ`:rCm;_DbEm3pa9Ŗq<g?e6acÖ¥f:ßaceæSolutionisasciisumofallplaintextchars
3efpjbpp<d?pAlri;kJ_:qCl;^DaEl3o`9Õp<f?Ê6acÔ¤f:ÝaceäSolêtionisasciisumofallplaintextchars
3deoiaoo<c?oAkqh;jJ^:pCk;]D`Ek3nŽ_9Á”o<e?È6acÒ£f:ÛaceâSolè®ionisasciisumofallplaintextchars
https://ideone.com/JvdMkA
language:
Java (HotSpot 12)
created:
25 days ago
visibility:
public

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