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ciphers/Vigenere.java

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+package ciphers;
+
+/**
+ * A Java implementation of Vigenere Cipher.
+ * @author  straiffix
+ */
+
+
+public class Vigenere  {
+
+    public  static String encrypt(final String message, final String key)
+    {
+
+        String result = "";
+
+        for (int i = 0, j = 0; i < message.length(); i++)
+        {
+            char c = message.charAt(i);
+            if (c >= 'A' && c <= 'Z') {
+                result += (char) ((c + key.toUpperCase().charAt(j) - 2 * 'A') % 26 + 'A');
+                j = ++j % key.length();
+            } else if (c >= 'a' && c <= 'z') {
+                result += (char) ((c + key.toLowerCase().charAt(j) - 2 * 'a') % 26 + 'a');
+                j = ++j % key.length();
+            } else {
+                result+=c;
+                continue;
+            }
+        }
+        return result;
+    }
+
+    public static String decrypt( final String message, final String key)
+    {
+        String result ="";
+
+        for(int i = 0, j = 0; i < message.length(); i++){
+
+            char c = message.charAt(i);
+            if((c >= 'A' && c <= 'Z')){
+                result += ((char)('Z'-(25-(c-key.toUpperCase().charAt(j)))%26));
+            }
+            else if(c >= 'a' && c <= 'z'){
+                result += ((char)('z'-(25-(c-key.toLowerCase().charAt(j)))%26));
+            }
+            else{
+                result+=c;
+                continue;
+            }
+            j = ++j % key.length();
+        }
+        return result;
+    }
+    public static void main (String [] args){
+        String text="Hello World!";
+        String key="itsakey";
+        System.out.println(text);
+        String ciphertext=encrypt(text, key);
+        System.out.println(ciphertext);
+        System.out.println(decrypt(ciphertext, key));
+
+    }
+}