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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.

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<?php

$success = 0;

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

$pdf = new COM("Chilkat.Pdf");

//  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 == 0) {
    print $pdf->LastErrorText . "\n";
    exit;
}

//  Options for signing are specified in JSON.
$json = new COM("Chilkat.JsonObject");

//  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 COM("Chilkat.Cert");
$success = $cert->LoadPfxFile('qa_data/pfx/myPdfSigningCert.pfx','secret');
if ($success == 0) {
    print $cert->LastErrorText . "\n";
    exit;
}

//  Tell the pdf object to use the certificate for signing.
$success = $pdf->SetSigningCert($cert);
if ($success == 0) {
    print $pdf->LastErrorText . "\n";
    exit;
}

$success = $pdf->SignPdf($json,'qa_output/hello_signed.pdf');
if ($success == 0) {
    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

?>