使用MD5WithRSA来签名和验签（.NET）

         /// <summary>
         /// 数字签名并返回BASE64编码的字符串
         /// </summary>
         /// <param name="contentForSign">待签名内容</param>
         /// <param name="privateKeyFile">私钥文件路径</param>
         /// <returns></returns>
         internal static string Sign(string contentForSign, string privateKeyFile)
         {
             var rsa = CcbRsaCryptProvider.GetInstanceForSign(privateKeyFile);
             var signData = rsa.SignData(Encoding.UTF8.GetBytes(contentForSign), new MD5CryptoServiceProvider());
             return Convert.ToBase64String(signData);
         }

         /// <summary>
         /// 验证签名
         /// </summary>
         /// <param name="contentForSign">待签名内容</param>
         /// <param name="signedData">签名内容</param>
         /// <param name="publicKeyFile">公钥文件路径</param>
         /// <returns>验证结果</returns>
         internal static bool VerifySign(string contentForSign, string signedData, string publicKeyFile)
         {
             var rsaPub = CcbRsaCryptProvider.GetInstanceForVerifySign(publicKeyFile);
             return rsaPub.VerifyData(Encoding.UTF8.GetBytes(contentForSign), new MD5CryptoServiceProvider(), Convert.FromBase64String(signedData));
         }