SSH Set Allowed Algorithms

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Demonstrates explicitly setting the algorithms allowed during SSH connection negotiation. A JsonObject supplies comma-separated allow-lists for the kex, hostKey, cipher, and mac categories, in order of preference, and is applied before connecting.

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

import 'package:chilkat/chilkat.dart';

void main() {
  // This example requires the Chilkat API to have been previously unlocked.
  // See Global Unlock Sample for sample code.

  // Demonstrates explicitly setting the algorithms allowed during SSH connection negotiation.
  // 
  // -------------------------------------------------------------------------------------------
  // Note: You typically should NOT explicitly set allowed algorithms.
  // By default, Chilkat orders algorithms according to best practices and accounts for known
  // vulnerabilities such as the "Terrapin Attack".  Hard-coding algorithms makes an application
  // brittle over time: if a server later changes its allowed algorithms, or if you connect to a
  // different server, the client and server may fail to agree on a mutually supported set.
  // -------------------------------------------------------------------------------------------

  final ssh = CkSsh();

  final json = CkJsonObject();

  // Algorithms supported by Chilkat, by category:
  // 
  // Key-exchange:  curve25519-sha256, curve25519-sha256@libssh.org, ecdh-sha2-nistp256,
  //   ecdh-sha2-nistp384, ecdh-sha2-nistp521, diffie-hellman-group14-sha256,
  //   diffie-hellman-group16-sha512, diffie-hellman-group18-sha512,
  //   diffie-hellman-group-exchange-sha256, diffie-hellman-group1-sha1,
  //   diffie-hellman-group14-sha1, diffie-hellman-group-exchange-sha1
  // 
  // Host key:  ssh-ed25519, ecdsa-sha2-nistp256, ecdsa-sha2-nistp384, ecdsa-sha2-nistp521,
  //   rsa-sha2-256, rsa-sha2-512, ssh-rsa, ssh-dss
  // 
  // Cipher:  chacha20-poly1305@openssh.com, aes128-ctr, aes256-ctr, aes192-ctr, aes128-cbc,
  //   aes256-cbc, aes192-cbc, aes128-gcm@openssh.com, aes256-gcm@openssh.com, twofish256-cbc,
  //   twofish128-cbc, blowfish-cbc
  // 
  // MAC:  hmac-sha2-256, hmac-sha2-512, hmac-sha2-256-etm@openssh.com,
  //   hmac-sha2-512-etm@openssh.com, hmac-sha1-etm@openssh.com, hmac-sha1, hmac-ripemd160,
  //   hmac-sha1-96, hmac-md5

  // List the allowed algorithms for each category, in order of preference.
  final allowedKex = 'curve25519-sha256@libssh.org,ecdh-sha2-nistp256';
  final allowedHostKey = 'ssh-ed25519,ecdsa-sha2-nistp256';
  final allowedCipher = 'chacha20-poly1305@openssh.com,aes256-ctr';
  final allowedMac = 'hmac-sha2-256,hmac-sha2-512';

  json.updateString('kex', allowedKex);
  json.updateString('hostKey', allowedHostKey);
  json.updateString('cipher', allowedCipher);
  json.updateString('mac', allowedMac);

  // Apply the allow-list.  This must be done before connecting.
  try {
    ssh.setAllowedAlgorithms(json);
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

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

  print('Connected.');

  ssh.disconnect();
}