added vigenere cipher

js/VigenereCipher.js

@@ -0,0 +1,82 @@
+<script>
+
+function getKey(str,key)
+{
+
+	key=key.split("");
+	if(str.length == key.length)
+		return key.join("");
+	else
+	{
+		let temp=key.length;
+		for (let i = 0;i<(str.length-temp) ; i++)
+		{
+
+			key.push(key[i % ((key).length)])
+		}
+	}
+	return key.join("");
+}
+
+
+function encrypt(str,key)
+{
+	let cipher_text="";
+
+	for (let i = 0; i < str.length; i++)
+	{
+		let x = (str[i].charCodeAt(0) + key[i].charCodeAt(0)) %26;
+
+		x += 'A'.charCodeAt(0);
+
+		cipher_text+=String.fromCharCode(x);
+	}
+	return cipher_text;
+}
+
+function dcrypt(cipher_text,key)
+{
+	let orig_text="";
+
+	for (let i = 0 ; i < cipher_text.length ; i++)
+	{
+		let z = (cipher_text[i].charCodeAt(0) -
+					key[i].charCodeAt(0) + 26) %26;
+
+		z += 'A'.charCodeAt(0);
+		orig_text+=String.fromCharCode(z);
+	}
+	return orig_text;
+}
+
+
+function LowToUpCase(s)
+{
+	let str =(s).split("");
+	for(let i = 0; i < s.length; i++)
+	{
+		if(s[i] == s[i].toLowerCase())
+		{
+			str[i] = s[i].toUpperCase();
+		}
+	}
+	s = str.toString();
+	return s;
+}
+
+let str = "hello world";
+let keyword = "tesla";
+
+
+let key = getKey(str, keyword);
+
+let cipher_text = encrypt(str, key);
+
+document.write("Encrypted message : "
+				+ cipher_text);
+
+document.write("Decrypted message : "
+				+ decrypt(cipher_text, key));
+
+
+</script>