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

public class ChilkatExample {

    public static void main(String[] args) {
        // 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.
        // -------------------------------------------------------------------------------------------

        Ssh ssh = new Ssh();

        JsonObject json = new JsonObject();

        // 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.
        String allowed_kex = "curve25519-sha256@libssh.org,ecdh-sha2-nistp256";
        String allowed_hostKey = "ssh-ed25519,ecdsa-sha2-nistp256";
        String allowed_cipher = "chacha20-poly1305@openssh.com,aes256-ctr";
        String allowed_mac = "hmac-sha2-256,hmac-sha2-512";

        json.updateString("kex", allowed_kex);
        json.updateString("hostKey", allowed_hostKey);
        json.updateString("cipher", allowed_cipher);
        json.updateString("mac", allowed_mac);

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

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

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

        ssh.disconnect();
    }
}