PHP Extension

SSH Authenticate using a Smart Card Private Key

Demonstrates using a private key stored on an HSM (smart card or token) for SSH public-key authentication. A JSON template locates the private and public key objects by class, key type, and label, and the returned handles are bound to an SshKey object.

Background: PKCS#11 objects are found by attribute rather than by name alone, which is why a template describing the class, key type, and label is used. An important practical detail is that the returned handles are valid only for the lifetime of the PKCS#11 session — they cannot be cached and reused later, so a subsequent session must locate the objects again. Logging out and closing the session when finished releases the device for other applications.

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<?php

include("chilkat.php");

$success = false;

//  This example requires the Chilkat API to have been previously unlocked.
//  See Global Unlock Sample for sample code.

//  Demonstrates using a private key stored on an HSM (smart card or token) for SSH public-key
//  authentication.  Public-key authentication means the client uses the private key, while the
//  corresponding public key is installed on the server under the SSH account.
//  
//  Note: Chilkat's PKCS#11 implementation runs on Windows, Linux, macOS, and other supported
//  operating systems.

$pkcs11 = new CkPkcs11();

//  Use the PKCS#11 driver (.dll, .so, or .dylib) for your particular HSM.
$pkcs11->put_SharedLibPath('C:/Program Files (x86)/Gemalto/IDGo 800 PKCS#11/IDPrimePKCS11.dll');

//  The HSM PIN should come from a secure source rather than being hard-coded.
$pin = '0000';

//  Normal user = 1
$userType = 1;

$success = $pkcs11->QuickSession($userType,$pin);
if ($success == false) {
    print $pkcs11->lastErrorText() . "\n";
    exit;
}

//  Provide a template describing the PKCS#11 object to find: an RSA private key labeled
//  "MySshKey".  For how such a key is originally imported, see
//  PKCS11 Import SSH Key
$jsonTemplate = new CkJsonObject();
$jsonTemplate->UpdateString('class','private_key');
$jsonTemplate->UpdateString('key_type','rsa');
$jsonTemplate->UpdateString('label','MySshKey');

$privKeyHandle = $pkcs11->FindObject($jsonTemplate);
if ($privKeyHandle == 0) {
    print $pkcs11->lastErrorText() . "\n";
    exit;
}

//  The handle is only valid for the duration of this PKCS#11 session.  To use the key in a
//  later session, find it again.
print 'private key handle: ' . $privKeyHandle . "\n";

//  Find the corresponding public key by changing the class in the same template.
$jsonTemplate->UpdateString('class','public_key');

$pubKeyHandle = $pkcs11->FindObject($jsonTemplate);
if ($pubKeyHandle == 0) {
    print $pkcs11->lastErrorText() . "\n";
    exit;
}

print 'public key handle: ' . $pubKeyHandle . "\n";

//  Create an empty SSH key object and tell it to use the PKCS#11 handles, indicating the key type.
$sshKey = new CkSshKey();
$success = $sshKey->UsePkcs11($pkcs11,$privKeyHandle,$pubKeyHandle,'rsa');
if ($success == false) {
    print $sshKey->lastErrorText() . "\n";
    exit;
}

$ssh = new CkSsh();

$port = 22;
$success = $ssh->Connect('ssh.example.com',$port);
if ($success == false) {
    print $ssh->lastErrorText() . "\n";
    exit;
}

//  Authentication uses the existing PKCS#11 session.  The signing happens on the smart card --
//  the private key never leaves the device.
$success = $ssh->AuthenticatePk('mySshLogin',$sshKey);
if ($success == false) {
    print $ssh->lastErrorText() . "\n";
    exit;
}

print 'Public-key authentication successful.' . "\n";

//  ... use the authenticated SSH session ...

$ssh->Disconnect();

$pkcs11->Logout();
$pkcs11->CloseSession();

?>