How to Resolve 'Could not establish a trust relationship for the SSL/TLS secure channel' Errors in C# SOAP Web Service Calls?

Solving the SSL/TLS trust relationship issue in C# SOAP web service calls

It can be frustrating to encounter the "Unable to establish trust relationship for SSL/TLS secure channel" error when calling a C# web service. This trust issue usually occurs when using SSL-protected web services and indicates an issue with the server's SSL certificate.

Check server configuration

First check the server configuration. Make sure the following conditions are met:

• The server's SSL certificate is valid and not self-signed.
• The hostname specified in the certificate matches the actual hostname of the server.

Potential causes of errors

If the server is configured properly, consider the following potential causes:

• Security settings on the client computer prevent a trust relationship for the server certificate.
• Firewall settings are blocking communication between client and server.

Disable certificate verification

As a temporary solution, disabling certificate verification can allow web service calls to continue. This is not recommended for production environments, but may be useful for testing purposes. The following code snippet provides a way to disable certificate verification:

<code class="language-csharp">// Lambda表达式，接受任何证书
System.Net.ServicePointManager.ServerCertificateValidationCallback =
    ((sender, certificate, chain, sslPolicyErrors) => true);

// Lambda表达式，信任发送者
System.Net.ServicePointManager.ServerCertificateValidationCallback
                = ((sender, cert, chain, errors) => cert.Subject.Contains("YourServerName"));

// 函数回调，用于验证证书
ServicePointManager.ServerCertificateValidationCallback += new RemoteCertificateValidationCallback(ValidateRemoteCertificate);</code>

Function verification example:

<code class="language-csharp">private static bool ValidateRemoteCertificate(object sender, X509Certificate cert, X509Chain chain, SslPolicyErrors policyErrors)
{
    bool result = cert.Subject.Contains("YourServerName");
    return result;
}</code>

These code snippets allow the web service to ignore certificate issues and establish the connection. However, it is important to thoroughly investigate the root cause of the trust issue and resolve it appropriately to ensure the future reliability of web service communications.

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