26

我有一个简单的应用程序，它使用 C# Web Client 类下载网站 HTML。这是我正在使用的代码的精简示例：

WebClient wc = new WebClient();
wc.Headers.Add("user-agent",
    "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.2; .NET CLR 1.0.3705;)");
htmlCode = wc.DownloadString("https://www.oig.hhs.gov/exclusions/exclusions_list.asp");

网站证书似乎有问题，因为我遇到了这个异常：

The underlying connection was closed: Could not establish trust relationship for the SSL/TLS secure channel." "The remote certificate is invalid according to the validation procedure.

如果您将链接复制并粘贴到浏览器中，则需要您同意风险，然后才能查看该网站。它是一个政府网站，所以我不担心任何病毒或任何东西。有没有办法告诉网络客户端绕过这个问题，并继续访问该站点？

4

5 回答 5

55

据我所知，这是因为他们使用了无效或过期的 SSL 证书。您可以使用以下方法绕过（忽略）它：

ServicePointManager.ServerCertificateValidationCallback += (sender, certificate, chain, sslPolicyErrors) => true;

2015年编辑：

这篇文章得到了很多人的支持，但我对我的回答感到遗憾。它可能会消除您的错误，但不会解决问题。接受任何 SSL 证书都会使您容易受到中间人攻击，因此这通常是一个非常糟糕的主意。我将保留此答案以供将来参考，但请注意，您应该尝试从根本上解决问题，即确保 SSL 证书有效。

于 2012-09-27T15:33:47.493 回答
16

试试这个：
您想要做的是将证书安装到您的本地计算机中。

如果它不在代码中，则该过程将执行以下操作：

  1. 以管理员模式（不是 Chrome）打开 Internet Explorer。
  2. 前往网站
  3. 选择继续
  4. 点击证书上的标题栏/网址栏，查看证书。
  5. 单击安装证书。

因此，您可以尝试查看这些其他问题，看看它们是否对您有帮助：

尝试安装证书并查看是否再次访问该 url，如果它要求继续。

****编辑**：
我阅读了网站证书，这是因为证书和网站的网址不匹配。

一个简单的改变是这样的：

htmlCode = wc.DownloadString("https://oig.hhs.gov/exclusions/exclusions_list.asp");

只需删除 www。

于 2012-09-27T15:41:05.237 回答
3

为了进一步构建 Leon Cullens 的答案，我想出了以下内容。就像他在回答中所说的那样，这不应该是您作为永久解决方案所做的事情，但如果您故意遇到此错误，这可能会对您有所帮助。这应该为您别无选择而只需要它工作的情况增加一点安全性。

我目前的情况是在开发目的期间，我需要使用自签名证书而不是真正的签名证书。这当然会导致以下错误......

“底层连接已关闭：无法为 SSL/TLS 安全通道建立信任关系。”

这是我所做的尝试使其更加安全并尝试避免“中间人攻击”。我试图让它尽可能简短和简单，但想确保我画了整个画面以便于理解。

using System;
using System.Text;
using System.Net;
using System.Net.Security;
using System.Security.Cryptography.X509Certificates;
using System.Threading;

namespace TestSecurity
{
    class TestDownload
    {
        private void client_DownloadProgressChanged(object sender, DownloadProgressChangedEventArgs e)
        {
            //Progress in the download
        }

        private void client_DownloadDataCompleted(object sender, DownloadDataCompletedEventArgs e)
        {
            //Download has completed
        }

        private bool client_RemoteCertificateValidation(object sender, X509Certificate certificate, X509Chain chain, SslPolicyErrors sslPolicyErrors)
        {
            if (sslPolicyErrors == SslPolicyErrors.RemoteCertificateChainErrors)
            {
                //Check to make sure the domain is correct
                X509Certificate2 certificate_details = (X509Certificate2)certificate;
                if (certificate_details.Thumbprint == "91A92CA60555DB51BEDDFE1AE4ECE54C8EBEBA97")
                {
                    #region Fingerprint for certificate
                    string storedFingerprint = "" +
                    "42048c788db687ed84407da10f78182e3487d1fc31c07ee131151f4e19b360ad2a8c452c2e7d614a5691d5479787fe70dabd" +
                    "64617465732e626c75656172726f77646576656c6f706d656e742e636f6d3110300e06035504080c0747656f72676961311f" +
                    "301d060355040a0c16426c7565204172726f7720446576656c6f706d656e74310b3009060355040613025553312f302d0609" +
                    "2a864886f70d0109011620737570706f727440626c75656172726f77646576656c6f706d656e742e636f6d31123010060355" +
                    "04070c09436c6576656c616e64301e170d3136303232393231313733335a170d3137303232383231313733335a3081b03129" +
                    "302706035504030c20757064617465732e626c75656172726f77646576656c6f706d656e742e636f6d3110300e0603550408" +
                    "42048c788db687ed84407da10f78182e3487d1fc31c07ee131151f4e19b360ad2a8c452c2e7d614a5691d5479787fe70dabd" +
                    "0613025553312f302d06092a864886f70d0109011620737570706f727440626c75656172726f77646576656c6f706d656e74" +
                    "2e636f6d3112301006035504070c09436c6576656c616e6430820122300d06092a864886f70d01010105000382010f003082" +
                    "010a0282010100a1cdf5af6f1bba5cc8495d8061895f39858fde814f5581266505bf4cbe0b26506278bc247963bb7c42f0b8" +
                    "b00638871932ed7d0a3c6562be8e5b513f24da2768051acde875b53bf94c8ea2cec397145db206b2524c42a2019a0bfa14e2" +
                    "a7ef0d311235e07b7e0363345fd7f397e365c0865b1b8fa8ad7eebdc1fcdce360db04f2822438621534ae10744155a710641" +
                    "9a69c16745974a37c5b06917036351b92c06540a6c70aa776c143eef6f7b8ec31c0c40a9eab8a399c9065bea688ea7bd1db2" +
                    "30af56d2ca0f8983f9e8dacb5613755fbcd8229d7042668a9130468a7480a2afde8c18bab895472ddf1ed2c49291c04e8cc2" +
                    "ff24db33d231b3a2498c03a5650203010001a34d304b301d0603551d0e0416041476b5c2c82ff138b87c0e2d6c046af4c634" +
                    "55040a0c16426c75652048c1f54dcb82e3487d1fc31c07ee1313fba9204c7b3232ba9204c7b323a021abcbda85bfca9c9931" +
                    "092a864886f70d01010b050003820101001ab0dfd318cc2e93a997445d0950ffcb63544c58fe1ded6e234aa7ccdcb5c890b1" +
                    "61b51ae08c1f54dcb3fbeca9c9932bde91d202b89c0b6f0af1a370017fa9f6a021abcbda85bfecebebc6d6067d4dc1e51ec5" +
                    "02cf95867516a84f01410cf80d7af4f0d3e9a86cf7b0323dba9204c7b3232c58b2289032a12aaa1ec4f64065da8bbde4fe47" +
                    "42048c788db687ed84407da10f78182e3487d1fc31c07ee131151f4e19b360ad2a8c452c2e7d614a5691d5479787fe70dabd" +
                    "de819522bb7ef870595d9738a6acdd39b7fcf6f36948ef2b404c2b6d7ebe577555148ad90013a5c2e812b2b907c808288040" +
                    "0db6702407585328f7e6c84b40451384391783001174d0";
                    #endregion

                    //Use the following to get the server's fingerprint to be saved and compared against
                    StringBuilder hex = new StringBuilder(certificate_details.RawData.Length * 2);
                    foreach (byte b in certificate_details.RawData)
                        hex.AppendFormat("{0:x2}", b);
                    string serverFingerprint = hex.ToString();

                    if (serverFingerprint == storedFingerprint) return true;
                    else return false;
                }
                else return false;
            }
            else if (sslPolicyErrors == SslPolicyErrors.None)
                return true;
            else
                return false;
        }

        public void TestDownload(Uri targetURL, bool useCredentials, string user, string pass)
        {
            WebClient client = new WebClient();
            bool taskCompleted = false;

            //Create the event handlers to monitor progress
            client.DownloadProgressChanged += new DownloadProgressChangedEventHandler(client_DownloadProgressChanged);
            client.DownloadDataCompleted += new DownloadDataCompletedEventHandler(client_DownloadDataCompleted);
            ServicePointManager.ServerCertificateValidationCallback += new RemoteCertificateValidationCallback(client_RemoteCertificateValidation);

            //Resolve the host
            IPHostEntry host = Dns.GetHostEntry(targetURL.Host);
            IPAddress ip = (host.AddressList.Length > 0 ? host.AddressList[0] : null);

            //Show the UI the resolved host

            //Account for credentials
            if (useCredentials)
            {
                NetworkCredential credentials = new NetworkCredential(
                    user,
                    pass);
                client.Credentials = credentials;
            }
            else client.Credentials = null;

            //Download file
            client.DownloadDataAsync(targetURL, taskCompleted);

            //Go to sleep until the file download has completed
            do { Thread.Sleep(500); } while (client.IsBusy);

            //File download complete

            //Destory the event handlers as they are no longer needed
            ServicePointManager.ServerCertificateValidationCallback -= client_RemoteCertificateValidation;
            client.DownloadProgressChanged -= client_DownloadProgressChanged;
            client.DownloadDataCompleted -= client_DownloadDataCompleted;
        }
    }
}
于 2016-02-29T22:56:52.100 回答
0

我对消息有这个问题：

无法为 SSL/TLS 安全通道建立信任关系。

我正在使用 .NET 客户端连接到 Apache 服务器上的 Web 服务。这就是为我解决问题的原因。

(proxy).UserAgent = "Apache-HttpClient/4.1.1 (java 1.5)";
于 2018-05-15T13:29:13.220 回答
0

根据这个答案，在使用 WebClient 实例之前添加这一行：

ServicePointManager.ServerCertificateValidationCallback = new        
RemoteCertificateValidationCallback(delegate { return true; });
于 2018-12-11T12:06:56.550 回答