PHP Extension

Sign PDF: Choosing RSASSA-PSS or PKCS1-v1_5 and Hash Algorithm

See more PDF Signatures Examples

This example demonstrates how to choose between RSASSA-PSS vs. PKCS1-v1_5 and the hash algorithm when signing a PDF. PHP Extension

<?php

include("chilkat.php");

$success = false;

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

$pdf = new CkPdf();

// Load a PDF to be signed.
// The "hello.pdf" is available at https://chilkatsoft.com/hello.pdf
$success = $pdf->LoadFile('qa_data/pdf/hello.pdf');
if ($success == false) {
    print $pdf->lastErrorText() . "\n";
    exit;
}

// Options for signing are specified in JSON.
$json = new CkJsonObject();

// In most cases, the signingCertificateV2 attribute is needed.
$json->UpdateInt('signingCertificateV2',1);

// ---------------------------------------------------------------------------------------------------------------------------
// This example is the same as the example at Sign a PDF (Simplest Example Possible)
// but with the following lines added to specify the signature scheme and hash algorithm.

// The signature schemes PKCS-v1_5 and RSASSA-PSS have differences. 
// PKCSV1_5 is deterministic. The same message and key will produce an identical signature value each time. 
// PSS is randomized and will produce a different signature value each time.

// To choose the hash algorithm:
// (The typical choices are sha1, sha256, sha384, and sha512.)
$json->UpdateString('hashAlgorithm','sha256');

// To choose PKCSV1_5:
$json->UpdateString('signingAlgorithm','pkcs');
// Alternatively, to choose RSASSA-PSS:
$json->UpdateString('signingAlgorithm','pss');

// If not specified, the default is SHA256 with PKCS-v1_5.

// The remainder of this example is the same as the example at Sign a PDF (Simplest Example Possible)
// ---------------------------------------------------------------------------------------------------------------------------

// Put the signature on page 1, top left
$json->UpdateInt('page',1);
$json->UpdateString('appearance.y','top');
$json->UpdateString('appearance.x','left');

// Use a font scale of 10.0
$json->UpdateString('appearance.fontScale','10.0');

// In this example, the appearance of the digital signature will contain three lines:
// 1) The signing certificate's common name
// 2) The current date/time
// 3) Some arbitrary text.
// The keyword "cert_cn" is replaced with the Certificate's Subject Common Name.
// The keyword "current_dt" is replaced with the current date/time.
// Any number of appearance text lines can be added.
$json->UpdateString('appearance.text[0]','Digitally signed by: cert_cn');
$json->UpdateString('appearance.text[1]','current_dt');
$json->UpdateString('appearance.text[2]','The crazy brown fox jumps over the lazy dog.');

// Load the signing certificate. (Use your own certificate.)
$cert = new CkCert();
$success = $cert->LoadPfxFile('qa_data/pfx/myPdfSigningCert.pfx','secret');
if ($success == false) {
    print $cert->lastErrorText() . "\n";
    exit;
}

// Tell the pdf object to use the certificate for signing.
$success = $pdf->SetSigningCert($cert);
if ($success == false) {
    print $pdf->lastErrorText() . "\n";
    exit;
}

$success = $pdf->SignPdf($json,'qa_output/hello_signed.pdf');
if ($success == false) {
    print $pdf->lastErrorText() . "\n";
    exit;
}

print 'The PDF has been successfully cryptographically signed.' . "\n";

// The appearance of the signature appears in Adobe Acrobat as shown here:

// (image:https://example-code.com/images/signature1.jpg/endImage)

?>