Dart

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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Dart

import 'package:chilkat/chilkat.dart';

void main() {
  // 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.

  final tunnel = CkSshTunnel();

  // List the allowed algorithms for each category, in order of preference.
  final json = 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.
  try {
    tunnel.setAllowedAlgorithms(json);
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  tunnel.destHostname = 'db.internal.example.com';
  tunnel.destPort = 5432;

  final sshPort = 22;
  try {
    tunnel.connect('ssh.example.com', sshPort);
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  print('Connected.');

  final waitForThreadExit = true;
  try {
    tunnel.closeTunnel(waitForThreadExit);
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }
}