SFTP Set Allowed SSH Algorithms

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Demonstrates the Chilkat SFtp.SetAllowedAlgorithms method, which configures the exact set of SSH algorithms permitted for the connection. 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.

import 'package:chilkat/chilkat.dart';

void main() {
  // Demonstrates the SFtp.SetAllowedAlgorithms method, which configures the exact set of SSH
  // algorithms permitted for the connection.  The only argument is a JsonObject.  It must be
  // called before Connect.
  // 
  // -------------------------------------------------------------------------------------------
  // 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 can make 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 sftp = CkSFtp();

  final json = CkJsonObject();

  // The 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 (encryption):
  //   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 (hash):
  //   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 key-exchange, host-key, cipher (encryption), and mac (hash) algorithms, 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 before connecting.
  try {
    sftp.setAllowedAlgorithms(json);
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

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

  print('Connected.');

  sftp.disconnect();
}