(PHP Extension) About RSA Public/Private Keys

This example provides some additional information for understanding public/private key pairs. In demonstrates how a private key is a superset of the public key. A public key contains the modulus and exponent. The matching private key also contains the modulus and exponent, but also contains the additional private key parts.

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<?php

// The version number (9_5_0) should match version of the Chilkat extension used, omitting the micro-version number.
// For example, if using Chilkat v9.5.0.48, then include as shown here:
include("chilkat_9_5_0.php");

$cert = new CkCert();

// Load a digital certificate.
$success = $cert->LoadFromFile('digitalCert.cer');
if ($success != true) {
    print $cert->lastErrorText() . "\n";
    exit;
}

// A .cer file does not contain the private key.  It should contain
// the public key...
// pubKey is a CkPublicKey
$pubKey = $cert->ExportPublicKey();

// Let's have a look at it (in XML format).
print 'Public Key from Certificate:' . "\n";
print $pubKey->getXml() . "\n";

// An RSA public key consists of a modulus and exponent.

// An RSA private key includes both the modulus and exponent,
// as well as other "big" numbers: P, Q, D, etc.

// Let's load an RSA private key from a DER-encoded file:
$privKey = new CkPrivateKey();

$success = $privKey->LoadAnyFormatFile('PrivateKey.key','');
if ($success != true) {
    print $privKey->lastErrorText() . "\n";

    exit;
}

// If this private key is the matching half to the public key from
// the certificate, then the modulus and exponent should
// be identical.  (Thus, a "private key" really contains both the public part as well as the private parts...).
print 'Private Key from DER:' . "\n";
print $privKey->getXml() . "\n";


?>