Merge pull request TheAlgorithms#1218 from Hassan-Elseoudy/master

nikhilkala · web-flow · commit 81612b4cbd2d · 2020-01-29T01:46:50.000+05:30
Simple Substitution Cipher Algorithm added.
diff --git a/ciphers/SimpleSubstitutionCipher.java b/ciphers/SimpleSubstitutionCipher.java
@@ -0,0 +1,97 @@
+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.
+ * 
+ * @author Hassan Elseoudy
+ */
+
+public class SimpleSubstitutionCipher {
+
+    /**
+     * 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;
+    }
+
+    /**
+     *
+     * TODO remove main and make JUnit Testing
+     */
+    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);
+    }
+
+}
