SSH Tunnel Set Allowed SSH Algorithms

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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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bool 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.

Chilkat.SshTunnel tunnel = new Chilkat.SshTunnel();

//  List the allowed algorithms for each category, in order of preference.
Chilkat.JsonObject json = new Chilkat.JsonObject();
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) {
    Debug.WriteLine(tunnel.LastErrorText);
    return;
}

tunnel.DestHostname = "db.internal.example.com";
tunnel.DestPort = 5432;

int sshPort = 22;
success = tunnel.Connect("ssh.example.com",sshPort);
if (success == false) {
    Debug.WriteLine(tunnel.LastErrorText);
    return;
}

Debug.WriteLine("Connected.");

bool waitForThreadExit = true;
success = tunnel.CloseTunnel(waitForThreadExit);
if (success == false) {
    Debug.WriteLine(tunnel.LastErrorText);
    return;
}