string strPath =  "aHR0cDovLzIwMy44MS4yOS40Njo1NTU3L1
9iYWlkdS9yaW5ncy9taWRpLzIwMDA3MzgwLTE2Lm1pZA==";         
    byte[] bpath = Convert.FromBase64String(strPath);
    strPath = System.Text.ASCIIEncoding.Default.GetString(bpath);

  System.Text.Encoding encode = System.Text.Encoding.ASCII ;
    byte[]  bytedata = encode.GetBytes( "test");
    string strPath = Convert.ToBase64String(bytedata,0,bytedata.Length);