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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Perl

use chilkat();

$success = 0;

#  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.

$tunnel = chilkat::CkSshTunnel->new();

#  List the allowed algorithms for each category, in order of preference.
$json = chilkat::CkJsonObject->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.
$success = $tunnel->SetAllowedAlgorithms($json);
if ($success == 0) {
    print $tunnel->lastErrorText() . "\r\n";
    exit;
}

$tunnel->put_DestHostname("db.internal.example.com");
$tunnel->put_DestPort(5432);

$sshPort = 22;
$success = $tunnel->Connect("ssh.example.com",$sshPort);
if ($success == 0) {
    print $tunnel->lastErrorText() . "\r\n";
    exit;
}

print "Connected." . "\r\n";

$waitForThreadExit = 1;
$success = $tunnel->CloseTunnel($waitForThreadExit);
if ($success == 0) {
    print $tunnel->lastErrorText() . "\r\n";
    exit;
}