Android™

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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// Important: Don't forget to include the call to System.loadLibrary
// as shown at the bottom of this code sample.
package com.test;

import android.app.Activity;
import com.chilkatsoft.*;

import android.widget.TextView;
import android.os.Bundle;

public class SimpleActivity extends Activity {

  private static final String TAG = "Chilkat";

  // Called when the activity is first created.
  @Override
  public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    boolean success = false;

    //  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.

    CkSshTunnel tunnel = new CkSshTunnel();

    //  List the allowed algorithms for each category, in order of preference.
    CkJsonObject json = new CkJsonObject();
    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.
    success = tunnel.SetAllowedAlgorithms(json);
    if (success == false) {
        Log.i(TAG, tunnel.lastErrorText());
        return;
        }

    tunnel.put_DestHostname("db.internal.example.com");
    tunnel.put_DestPort(5432);

    int sshPort = 22;
    success = tunnel.Connect("ssh.example.com",sshPort);
    if (success == false) {
        Log.i(TAG, tunnel.lastErrorText());
        return;
        }

    Log.i(TAG, "Connected.");

    boolean waitForThreadExit = true;
    success = tunnel.CloseTunnel(waitForThreadExit);
    if (success == false) {
        Log.i(TAG, tunnel.lastErrorText());
        return;
        }


  }

  static {
      System.loadLibrary("chilkat");

      // Note: If the incorrect library name is passed to System.loadLibrary,
      // then you will see the following error message at application startup:
      //"The application <your-application-name> has stopped unexpectedly. Please try again."
  }
}