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  1. public class Main {
  2.     public static void main(String[] args) {
  3.         int[] ciphertext = {
  4.             102, 141, 142, 161, 148, 131, 158, 157, 120, 131, 
  5.             126, 153, 130, 143, 154, 135, 118, 137, 148, 111, 
  6.             116, 145, 134, 133, 118, 103, 136, 107, 138, 127, 
  7.             102, 131, 194, 99, 114, 200, 202, 127, 120, 105, 
  8.             126, 202, 108, 194, 198, 214, 222, 204, 116, 224, 
  9.             194, 198, 202, 230, 166, 222, 216, 234, 232, 210, 
  10.             222, 220, 210, 230, 194, 230, 198, 210, 210, 230, 
  11.             234, 218, 222, 204, 194, 216, 216, 224, 216, 194, 
  12.             210, 220, 232, 202, 240, 232, 198, 208, 194, 228, 230
  13.         };
  14.  
  15.         decrypt(ciphertext);
  16.     }
  17.  
  18.     public static void decrypt(int[] ct) {
  19.         int length = ct.length;
  20.         System.out.println("Ciphertext length: " + length + " characters");
  21.         System.out.println("Testing possible keys from " + (length/2) + " to " + length);
  22.  
  23.         for (int initialKey = length/2; initialKey <= length; initialKey++) {
  24.             StringBuilder plaintext = new StringBuilder();
  25.             boolean valid = true;
  26.             int currentKey = initialKey;
  27.  
  28.             for (int encrypted : ct) {
  29.                 boolean found = false;
  30.                 // Try all possible ASCII characters (32-126)
  31.                 for (int c = 32; c <= 126; c++) {
  32.                     if (c + (c % currentKey) == encrypted) {
  33.                         plaintext.append((char)c);
  34.                         found = true;
  35.                         break;
  36.                     }
  37.                 }
  38.  
  39.                 if (!found) {
  40.                     valid = false;
  41.                     break;
  42.                 }
  43.  
  44.                 currentKey++;
  45.             }
  46.  
  47.             if (valid) {
  48.                 System.out.println("\nFound valid decryption with initial key " + initialKey + ":");
  49.                 System.out.println(plaintext.toString());
  50.                 return;
  51.             }
  52.         }
  53.  
  54.         System.out.println("No valid decryption found with standard ASCII characters.");
  55.     }
  56. }
Success #stdin #stdout 0.13s 57864KB
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stdin
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Standard input is empty
stdout
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Ciphertext length: 91 characters
Testing possible keys from 45 to 91

Found valid decryption with initial key 66:
3hismess<g?sAoMl;nJb:tCo;aDdEo3rac9des<i?e6ackof:pacesSolutionisasciisumofallplaintextchars
https://ideone.com/rRkS2c
language:
Java (HotSpot 12)
created:
25 days ago
visibility:
public

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