Merge pull request TheAlgorithms#58 from jonathangomz/patch-1

Create vigenereCipher.js

Author: ms10398

Ciphers/vigenereCipher.js

@@ -0,0 +1,81 @@
+/**
+ * Check if the Character is letter or not
+ * @param {String} character - character to check
+ * @return {object} An array with the character or null if isn't a letter
+ */
+function isLetter(str) {
+  return str.length === 1 && str.match(/[a-zA-Z]/i);
+}
+
+/**
+ * Check if is Uppercase or Lowercase
+ * @param {String} character - character to check
+ * @return {Boolean} result of the checking
+ */
+function isUpperCase(character){
+  if (character == character.toUpperCase()) {
+    return true;
+  }
+  if (character == character.toLowerCase()){
+    return false;
+  }
+}
+
+/**
+ * Encrypt a Vigenere cipher
+ * @param {String} message - string to be encrypted
+ * @param {String} key - key for encrypt
+ * @return {String} result - encrypted string
+ */
+function encrypt(message, key)
+{
+
+  let result = "";
+
+  for (let i = 0, j = 0; i < message.length; i++) {
+    let c = message.charAt(i);
+    if (isLetter(c)){
+      if(isUpperCase(c)) {
+        result += String.fromCharCode((c.charCodeAt(0) + key.toUpperCase().charCodeAt(j) - 2 * 65) % 26 + 65); // A: 65
+      } else {
+        result += String.fromCharCode((c.charCodeAt(0) + key.toLowerCase().charCodeAt(j) - 2 * 97) % 26 + 97); // a: 97
+      }
+    } else {
+      result+=c;
+    }
+    j = ++j % key.length;
+  }
+  return result;
+}
+
+/**
+ * Decrypt a Vigenere cipher
+ * @param {String} message - string to be decrypted
+ * @param {String} key - key for decrypt
+ * @return {String} result - decrypted string
+ */
+function decrypt(message, key)
+{
+  let result ="";
+
+  for(let i = 0, j = 0; i < message.length; i++){
+    let c = message.charAt(i);
+    if (isLetter(c)){
+      if(isUpperCase(c)) {
+        result += String.fromCharCode(90-(25-(c.charCodeAt(0)-key.toUpperCase().charCodeAt(j)))%26);
+      } else {
+        result += String.fromCharCode(122-(25-(c.charCodeAt(0)-key.toLowerCase().charCodeAt(j)))%26);
+      }
+    } else {
+      result+=c;
+    }
+    j = ++j % key.length;
+  }
+  return result;
+}
+
+let messageEncrypt = encrypt('Hello World!', 'code');
+console.log(messageEncrypt); // "Jhpnr Yrvng!"
+
+let messageDecrypt = decrypt('Jsopq Zstzg!', 'code');
+console.log(messageDecrypt); // "Hello World!"