将32位MD5摘要串转换为128位二进制字符串

将32为MD5摘要串转换为128位二进制字符串：

        /// <summary>
        /// 将字符串转成二进制
        /// </summary>
        /// <param name="s">源字符串</param>
        /// <returns>二进制串</returns>
        internal static string ConvertStringToBinary(string s)
        {
            if (s.IsNullOrWhiteSpace())
            {
                throw new ArgumentNullException("源字符串为空", s);
            }
            if (s.Length != 32)
            {
                throw new ArgumentNullException("源字符串长度无效", s);
            }
            var bitBuilder = new StringBuilder(128);
            for (var i = 0; i < s.Length; i += 2)
            {
                var tem = Convert.ToInt32(s.Substring(i, 2), 16);
                bitBuilder.Append(Convert.ToString(tem, 2).PadLeft(8, '0'));
            }
            return bitBuilder.ToString();
        }