C# ssl debug

The .NET Framework 4.8 does not have a direct built-in equivalent to Java's -Djavax.net.debug=ssl:handshake for enabling SSL/TLS handshake debugging from the command line or via a simple configuration switch. However, you can achieve similar diagnostic output using the following approaches:

1. Enable System.Net Tracing (Recommended for .NET Framework)

You can configure System.Net tracing via your application's app.config or web.config file to log detailed information about network activity, including SSL/TLS handshakes.

Example app.config:

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<configuration>

  <system.diagnostics>

    <sources>

      <source name="System.Net" switchName="sourceSwitch" switchType="System.Diagnostics.SourceSwitch">

        <listeners>

          <add name="console"/>

        </listeners>

      </source>

      <source name="System.Net.Sockets" switchName="sourceSwitch" switchType="System.Diagnostics.SourceSwitch">

        <listeners>

          <add name="console"/>

        </listeners>

      </source>

    </sources>

    <switches>

      <!-- Set to "Verbose" for maximum detail -->

      <add name="sourceSwitch" value="Verbose"/>

    </switches>

    <sharedListeners>

      <add name="console" type="System.Diagnostics.TextWriterTraceListener" initializeData="network.log"/>

    </sharedListeners>

    <trace autoflush="true"/>

  </system.diagnostics>

</configuration>

This logs System.Net and System.Net.Sockets activity to a file (network.log).

While it doesn’t dump raw TLS handshake bytes like Java, it does show certificate validation, cipher suites negotiation (indirectly), and connection errors.

For more TLS-specific diagnostics, combine this with Windows-level tools (see below).

⚠️ Note: Tracing impacts performance—use only for debugging. 

2. Use Windows Schannel Logging (OS-Level SSL Debugging)

.NET Framework uses the Windows Schannel (Secure Channel) security package for TLS. You can enable Schannel event logging via the Windows Event Log:

Open Event Viewer → Applications and Services Logs → Microsoft → Windows → Schannel.

Right-click Operational → Enable Log.

Reproduce your SSL issue; handshake errors and details will appear here.