Encryption & Decryption passwords in C#

Encrypt and Decrypt a string using dual encryption method.

using System;
using System.Security.Cryptography;
using System.Text;
using System.Text.RegularExpressions;

namespace Pass
{
    public class EncryptDecrypt
    {
        /// <summary>
        /// Encrypt a string using dual encryption method. Return a encrypted cipher Text
        /// </summary>
        /// <param name="toEncrypt"></param>
        /// <param name="key"></param>
        /// <returns></returns>
        public static string Encrypt(string toEncrypt, string key)
        {
            byte[] keyArray;
            byte[] toEncryptArray = Encoding.UTF8.GetBytes(toEncrypt);
            MD5CryptoServiceProvider hashmd5 = new MD5CryptoServiceProvider();
            keyArray = hashmd5.ComputeHash(UTF8Encoding.UTF8.GetBytes(key));
            hashmd5.Clear();
            TripleDESCryptoServiceProvider tdes = new TripleDESCryptoServiceProvider
            {
                Key = keyArray,
                Mode = CipherMode.ECB,
                Padding = PaddingMode.PKCS7
            };
            ICryptoTransform cTransform = tdes.CreateEncryptor();
            byte[] resultArray = cTransform.TransformFinalBlock(toEncryptArray, 0, toEncryptArray.Length);
            tdes.Clear();
            string resultbase64String = Convert.ToBase64String(resultArray, 0, resultArray.Length);
            string resultEncodedString = UrlHelper.Encode(resultbase64String);
            return resultEncodedString;
        }

        public static string Decrypt(string cipherString, string key)
        {
            try
            {
                byte[] keyArray;
                string cipherDecodedString = UrlHelper.Decode(cipherString);
                byte[] toEncryptArray = Convert.FromBase64String((cipherDecodedString.Replace(' ', '+')));
                MD5CryptoServiceProvider hashmd5 = new MD5CryptoServiceProvider();
                keyArray = hashmd5.ComputeHash(Encoding.UTF8.GetBytes(key));
                hashmd5.Clear();
                TripleDESCryptoServiceProvider tdes = new TripleDESCryptoServiceProvider
                {
                    Key = keyArray,
                    Mode = CipherMode.ECB,
                    Padding = PaddingMode.PKCS7
                };
                ICryptoTransform cTransform = tdes.CreateDecryptor();
                byte[] resultArray = cTransform.TransformFinalBlock(toEncryptArray, 0, toEncryptArray.Length);
                tdes.Clear();
                return Encoding.UTF8.GetString(resultArray);
            }
            catch (Exception ex)
            {
                return "";
            }
        }
    }

    public class UrlHelper
    {
        public static string Encode(string str)
        {
            var charClass = String.Format("0-9a-zA-Z{0}", Regex.Escape("-_.!~*'()"));
            return Regex.Replace(str, string.Format("[^{0}]", charClass), new MatchEvaluator(EncodeEvaluator));
        }

        public static string EncodeEvaluator(Match match)
        {
            return (match.Value == " ") ? "+" : string.Format("%{0:X2}", Convert.ToInt32(match.Value[0]));
        }

        public static string DecodeEvaluator(Match match)
        {
            return Convert.ToChar(int.Parse(match.Value.Substring(1), System.Globalization.NumberStyles.HexNumber)).ToString();
        }

        public static string Decode(string str)
        {
            return Regex.Replace(str.Replace('+', ' '), "%[0-9a-zA-Z][0-9a-zA-Z]", new MatchEvaluator(DecodeEvaluator));
        }
    }
}

Usage

namespace Pass
{
    class Program
    {
        static void Main(string[] args)
        {
            string passkey = "123";
            string pwd = "Ridhvi";
            string encryptedPass = EncryptDecrypt.Encrypt(pwd, passkey);
            string decryptedPass = EncryptDecrypt.Decrypt(encryptedPass, passkey);
        }
    }
}