2023-06-27 C#: System.Net.WebException: '要求已經中止: 無法建立 SSL/TLS 的安全通道。'

When I am trying to create a connection by C#. Some web will throw “System.Net.WebException: '要求已經中止: 無法建立 SSL/TLS 的安全通道。'” error exception.

Solution

Add this code piece before create link

System.Net.ServicePointManager.ServerCertificateValidationCallback = delegate { return true; };
System.Net.ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12 | SecurityProtocolType.Ssl3 | SecurityProtocolType.Tls;

So, my code become as follows:

        private void TASK_DownloadStart()
        {
            // 開始下載
            System.Net.ServicePointManager.ServerCertificateValidationCallback = delegate { return true; };
            System.Net.ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12 | SecurityProtocolType.Ssl3 | SecurityProtocolType.Tls;
            WebRequest request = WebRequest.Create(textBox_url.Text);
            WebResponse response = request.GetResponse();

            Stream data = response.GetResponseStream();
            string html = String.Empty;
            using (StreamReader sr = new StreamReader(data))
            {
                html = sr.ReadToEnd();
            }
            richTextBox_Log.AppendText(html);
            richTextBox_Log.ScrollToCaret();
        }

Note that this solution need .NET 4.5+

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2023-06-27 C#: System.Net.WebException: '要求已經中止: 無法建立 SSL/TLS 的安全通道。'

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