checksum MD5

gistfile1.cs

 using (var md5 = new MD5CryptoServiceProvider())
            {
                var retVal = md5.ComputeHash(file);
                var sb = new StringBuilder();
                for (int i = 0; i < retVal.Length; i++)
                    sb.Append(retVal[i].ToString("x2"));
                return Json(sb.ToString());
            }