Java

SSH Tunnel Set Allowed SSH Algorithms

Demonstrates the Chilkat SshTunnel.SetAllowedAlgorithms method, which restricts the SSH connection to a specific set of algorithms. A JsonObject supplies comma-separated allow-lists for the kex, hostKey, cipher, and mac categories. It must be called before Connect.

Important: You typically should not set allowed algorithms explicitly. By default Chilkat orders algorithms according to best practices and accounts for known vulnerabilities.

Background: SSH negotiates a mutually supported algorithm from each category at connection time, and pinning that choice makes an application brittle: if the server later drops a weak algorithm, the two sides may fail to agree and the tunnel stops working. The legitimate reasons to override are a security policy mandating specific algorithms or a compatibility problem with an old server; otherwise let the library's defaults evolve with current guidance.

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import com.chilkatsoft.chilkat2.ChilkatException;
import com.chilkatsoft.chilkat2.JsonObject;
import com.chilkatsoft.chilkat2.SshTunnel;

public class ChilkatExample {

    public static void main(String[] args) {
        // Demonstrates the SshTunnel.SetAllowedAlgorithms method, which restricts the SSH connection to a
        // specific set of algorithms.  The only argument is a JsonObject.  It must be called before
        // Connect.
        //
        // Note: You typically should NOT set allowed algorithms explicitly.  By default Chilkat orders
        // algorithms according to best practices and accounts for known vulnerabilities.  Hard-coding
        // them can make an application brittle if a server later changes its allowed algorithms.

        SshTunnel tunnel = new SshTunnel();

        // List the allowed algorithms for each category, in order of preference.
        JsonObject json = new JsonObject();
        json.updateString("kex", "curve25519-sha256@libssh.org,ecdh-sha2-nistp256");
        json.updateString("hostKey", "ssh-ed25519,ecdsa-sha2-nistp256");
        json.updateString("cipher", "chacha20-poly1305@openssh.com,aes256-ctr");
        json.updateString("mac", "hmac-sha2-256,hmac-sha2-512");

        // Apply the allow-list before connecting.
        try {
            tunnel.setAllowedAlgorithms(json);
        } catch (ChilkatException e) {
            System.out.println(e.getLastErrorText());
            return;
        }

        tunnel.setDestHostname("db.internal.example.com");
        tunnel.setDestPort(5432);

        int sshPort = 22;
        try {
            tunnel.connect("ssh.example.com", sshPort);
        } catch (ChilkatException e) {
            System.out.println(e.getLastErrorText());
            return;
        }

        System.out.println("Connected.");

        boolean waitForThreadExit = true;
        try {
            tunnel.closeTunnel(waitForThreadExit);
        } catch (ChilkatException e) {
            System.out.println(e.getLastErrorText());
            return;
        }
    }
}