From 8bbb56231e239ad12dc706122db6bce804ff5802 Mon Sep 17 00:00:00 2001
From: Smriti Dube <140499593+smritii73@users.noreply.github.com>
Date: Sun, 27 Oct 2024 13:54:39 +0530
Subject: [PATCH] Create VernamCipher.java

Vernam Cipher is implemented when key length is equal to the size of plaintext
---
 VernamCipher.java | 49 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 49 insertions(+)
 create mode 100644 VernamCipher.java

diff --git a/VernamCipher.java b/VernamCipher.java
new file mode 100644
index 000000000..8d269c1b5
--- /dev/null
+++ b/VernamCipher.java
@@ -0,0 +1,49 @@
+import java.util.Scanner;
+public class VernamCipher {
+    public static String vc(String pt, String k) {
+        if (pt.length() != k.length()) {
+            throw new IllegalArgumentException("Key must be the same length as the plaintext.");
+        }
+        StringBuilder ct = new StringBuilder();
+        for (int i = 0; i < pt.length(); i++) {
+            ct.append((char) (pt.charAt(i) ^ k.charAt(i)));
+        }
+        return ct.toString();
+    }
+    public static String vernamDecipher(String ct, String k) {
+        if (ct.length() != k.length()) {
+            throw new IllegalArgumentException("Key must be the same length as the ciphertext.");
+        }
+        StringBuilder pt = new StringBuilder();
+        for (int i = 0; i < ct.length(); i++) {
+            pt.append((char) (ct.charAt(i) ^ k.charAt(i)));
+        }
+        return pt.toString();
+    }
+    public static void bruteForceDecrypt(String ct, String k) {
+        char[] possibleKeys = {'A', 'B', 'C', 'D', 'E'};
+        for (char key : possibleKeys) {
+            StringBuilder decrypted = new StringBuilder();
+            for (int i = 0; i < ct.length(); i++) {
+                decrypted.append((char) (ct.charAt(i) ^ key));
+            }
+            System.out.println("Attempt with key '" + key + "': " + decrypted);
+        }
+    }
+    public static void main(String[] args) {
+        Scanner scanner = new Scanner(System.in);
+        System.out.print("Enter plaintext (pt): ");
+        String pt = scanner.nextLine();
+        System.out.print("Enter key (k, must be the same length as the plaintext): ");
+        String k = scanner.nextLine();
+        try {
+            String ct = vc(pt, k);
+            System.out.println("Ciphertext (ct): " + ct);
+            System.out.println("Decrypted plaintext (pt): " + vernamDecipher(ct, k));
+        } catch (IllegalArgumentException e) {
+            System.out.println(e.getMessage());
+        }
+        System.out.println("\nBrute-force Decrypt Attempts:");
+        bruteForceDecrypt(pt, k);
+    }
+}