Rust

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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Rust


// 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.

let tunnel = chilkat::SshTunnel::new();

// List the allowed algorithms for each category, in order of preference.
let json = chilkat::JsonObject::new();
let _ = json.update_string("kex", "curve25519-sha256@libssh.org,ecdh-sha2-nistp256");
let _ = json.update_string("hostKey", "ssh-ed25519,ecdsa-sha2-nistp256");
let _ = json.update_string("cipher", "chacha20-poly1305@openssh.com,aes256-ctr");
let _ = json.update_string("mac", "hmac-sha2-256,hmac-sha2-512");

// Apply the allow-list before connecting.
if tunnel.set_allowed_algorithms(&json).is_err() {
    println!("{}", tunnel.last_error_text());
    return;
}

tunnel.set_dest_hostname("db.internal.example.com");
tunnel.set_dest_port(5432);

let ssh_port = 22;
if tunnel.connect("ssh.example.com", ssh_port).is_err() {
    println!("{}", tunnel.last_error_text());
    return;
}

println!("Connected.");

let wait_for_thread_exit = true;
if tunnel.close_tunnel(wait_for_thread_exit).is_err() {
    println!("{}", tunnel.last_error_text());
    return;
}