From 7ca58d6f8c9a52b7bf449b7a049091e37fdb68e8 Mon Sep 17 00:00:00 2001
From: patrick-steve <75305373+patrick-steve@users.noreply.github.com>
Date: Thu, 21 Oct 2021 21:33:28 +0530
Subject: [PATCH] Add Substitution Cipher (#2694)

---
 Ciphers/simpleSubCipher.java | 92 ++++++++++++++++++++++++++++++++++++
 1 file changed, 92 insertions(+)
 create mode 100644 Ciphers/simpleSubCipher.java

diff --git a/Ciphers/simpleSubCipher.java b/Ciphers/simpleSubCipher.java
new file mode 100644
index 000000000..779ca9b3a
--- /dev/null
+++ b/Ciphers/simpleSubCipher.java
@@ -0,0 +1,92 @@
+package ciphers;
+ 
+import java.util.*;
+ 
+/**
+ *
+ * The simple substitution cipher is a cipher that has been in use for many hundreds of years 
+ * (an excellent history is given in Simon Singhs 'the Code Book'). 
+ * It basically consists of substituting every plaintext character for a different ciphertext character. 
+ * It differs from the Caesar cipher in that the cipher alphabet is not simply the alphabet shifted,
+ * it is completely jumbled.
+ * 
+ */
+ 
+public class simpleSubCipher {
+ 
+    /**
+     * Encrypt text by replacing each element with its opposite character.
+     *
+     * @param message
+     * @param cipherSmall
+     * @return Encrypted message
+     */
+    public static String encode(String message, String cipherSmall) {
+        String encoded = "";
+ 
+        // This map is used to encode
+        Map<Character,Character> cipherMap = new HashMap<Character,Character>();
+ 
+        char beginSmallLetter = 'a';
+        char beginCapitalLetter = 'A';
+ 
+        cipherSmall = cipherSmall.toLowerCase();
+        String cipherCapital = cipherSmall.toUpperCase();
+ 
+        // To handle Small and Capital letters
+        for(int i = 0; i < cipherSmall.length(); i++){
+            cipherMap.put(beginSmallLetter++,cipherSmall.charAt(i));
+            cipherMap.put(beginCapitalLetter++,cipherCapital.charAt(i));
+        }
+ 
+        for(int i = 0; i < message.length(); i++){
+            if(Character.isAlphabetic(message.charAt(i)))
+                encoded += cipherMap.get(message.charAt(i));
+            else
+                encoded += message.charAt(i);
+        }
+ 
+        return encoded;
+    }
+ 
+    /**
+     * Decrypt message by replacing each element with its opposite character in cipher.
+     *
+     * @param encryptedMessage
+     * @param cipherSmall
+     * @return message
+     */
+    public static String decode(String encryptedMessage, String cipherSmall) {
+        String decoded = "";
+ 
+ 
+        Map<Character,Character> cipherMap = new HashMap<Character,Character>();
+ 
+        char beginSmallLetter = 'a';
+        char beginCapitalLetter = 'A';
+ 
+        cipherSmall = cipherSmall.toLowerCase();
+        String cipherCapital = cipherSmall.toUpperCase();
+ 
+        for(int i = 0; i < cipherSmall.length(); i++){
+            cipherMap.put(cipherSmall.charAt(i),beginSmallLetter++);
+            cipherMap.put(cipherCapital.charAt(i),beginCapitalLetter++);
+        }
+ 
+        for(int i = 0; i < encryptedMessage.length(); i++){
+            if(Character.isAlphabetic(encryptedMessage.charAt(i)))
+                decoded += cipherMap.get(encryptedMessage.charAt(i));
+            else
+                decoded += encryptedMessage.charAt(i);
+        }
+ 
+        return decoded;
+    }
+ 
+    public static void main(String[] args) {
+        String a = encode("defend the east wall of the castle","phqgiumeaylnofdxjkrcvstzwb");
+        String b = decode(a,"phqgiumeaylnofdxjkrcvstzwb");
+        System.out.println(b);
+    }
+ 
+}