System.Net.Security.SslStream.AuthenticateAsClient

This topic describes the AuthenticateAsClient method of the SslStream class, which is used to establish a secure client connection.

Syntax

The SslStream.AuthenticateAsClient method is used by the client side of a Secure Sockets Layer (SSL) connection to establish a secure channel with a server. This method initiates the SSL handshake process.

Parameters

Return Value

true if the authentication was successful; otherwise, false.

Exceptions

• ArgumentNullException: If targetHost is null.
• ArgumentException: If targetHost is an empty string.
• System.Net.Sockets.SocketException: If a socket error occurs during the handshake.
• System.ComponentModel.Win32Exception: If an underlying Windows SChannel error occurs.

Remarks

The AuthenticateAsClient method must be called before any data is sent or received over the SslStream. The targetHost parameter is crucial for verifying the server's identity. If the server's certificate does not match the specified targetHost, the authentication will fail.

When providing client certificates, ensure they are valid and trusted by the server.

Example

using System;
using System.Net.Security;
using System.Net.Sockets;
using System.Security.Cryptography.X509Certificates;
using System.Threading.Tasks;

public class SslClientExample
{
    public static async Task ConnectAndCommunicateAsync(string host, int port)
    {
        using (TcpClient client = new TcpClient())
        {
            await client.ConnectAsync(host, port);
            using (SslStream sslStream = new SslStream(client.GetStream(), false))
            {
                try
                {
                    // Authenticate the client
                    // Use the server's hostname for targetHost validation
                    // No client certificate is provided in this example
                    await sslStream.AuthenticateAsClientAsync(host);

                    Console.WriteLine("SSL handshake completed successfully.");

                    // Now you can send and receive data securely
                    byte[] message = System.Text.Encoding.UTF8.GetBytes("Hello, server!");
                    await sslStream.WriteAsync(message, 0, message.Length);
                    await sslStream.FlushAsync();

                    byte[] buffer = new byte[2048];
                    int bytesRead = await sslStream.ReadAsync(buffer, 0, buffer.Length);
                    string response = System.Text.Encoding.UTF8.GetString(buffer, 0, bytesRead);
                    Console.WriteLine($"Server response: {response}");
                }
                catch (Exception ex)
                {
                    Console.WriteLine($"Authentication failed: {ex.Message}");
                }
            }
        }
    }

    public static async Task Main(string[] args)
    {
        // Replace with your target server details
        string serverHost = "example.com";
        int serverPort = 443;

        await ConnectAndCommunicateAsync(serverHost, serverPort);
    }
}
            

See Also

• SslStream Class
• SslStream.AuthenticateAsServer
• System.Net.Security Namespace