Code
using System.Web.Configuration;
using System.Reflection;


        private void button1_Click(object sender, EventArgs e)
        {
            MessageBox.Show(EncodePassword("1", "Ehk/gwOk7mpqna7M/8hc5g=="));
        }


        public string EncodePassword(string pass, string salt)
        {
            byte[] bIn = Encoding.Unicode.GetBytes(pass);
            byte[] bSalt = Convert.FromBase64String(salt);
            byte[] bAll = new byte[bSalt.Length + bIn.Length];
            byte[] bRet = null;

            Buffer.BlockCopy(bSalt, 0, bAll, 0, bSalt.Length);
            Buffer.BlockCopy(bIn, 0, bAll, bSalt.Length, bIn.Length);

            bRet = EncryptPassword(bAll);
            return Convert.ToBase64String(bRet);
        }
        public virtual byte[] EncryptPassword(byte[] password)
        {
            Type machineKeySection = typeof(MachineKeySection);
            Type[] paramTypes = new Type[] { typeof(bool), typeof(byte[]), typeof(byte[]), typeof(int), typeof(int) };
            MethodInfo encryptOrDecryptData = machineKeySection.GetMethod("EncryptOrDecryptData", BindingFlags.Static | BindingFlags.NonPublic, null, paramTypes, null);

            return (byte[])encryptOrDecryptData.Invoke(null, new object[] { true, password, null, 0, password.Length });
        }