PHP ActiveX

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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<?php

$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 = new COM("Chilkat.SshTunnel");

//  List the allowed algorithms for each category, in order of preference.
$json = new COM("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 == 0) {
    print $tunnel->LastErrorText . "\n";
    exit;
}

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

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

print 'Connected.' . "\n";

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


?>