Perl

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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Chilkat2 Perl

use strict;
use warnings;
use Chilkat2;

# 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.

my $tunnel = Chilkat2::SshTunnel->new;

# List the allowed algorithms for each category, in order of preference.
my $json = Chilkat2::JsonObject->new;
$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.
my $success = $tunnel->SetAllowedAlgorithms($json);
if (!$success) {
    print $tunnel->LastErrorText, "\n";
    exit;
}

$tunnel->DestHostname('db.internal.example.com');
$tunnel->DestPort(5432);

my $sshPort = 22;
$success = $tunnel->Connect('ssh.example.com', $sshPort);
if (!$success) {
    print $tunnel->LastErrorText, "\n";
    exit;
}

print "Connected.\n";

my $waitForThreadExit = 1;
$success = $tunnel->CloseTunnel($waitForThreadExit);
if (!$success) {
    print $tunnel->LastErrorText, "\n";
    exit;
}