(Perl) 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.

Chilkat Perl Downloads Perl Module for Windows, MacOS, Linux, Alpine Linux, Solaris

use chilkat();

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

$pdf = chilkat::CkPdf->new();

# 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() . "\r\n";
    exit;
}

# Options for signing are specified in JSON.
$json = chilkat::CkJsonObject->new();

# 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 = chilkat::CkCert->new();
$success = $cert->LoadPfxFile("qa_data/pfx/myPdfSigningCert.pfx","secret");
if ($success == 0) {
    print $cert->lastErrorText() . "\r\n";
    exit;
}

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

$success = $pdf->SignPdf($json,"qa_output/hello_signed.pdf");
if ($success == 0) {
    print $pdf->lastErrorText() . "\r\n";
    exit;
}

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

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