Java

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

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This example demonstrates how to choose between RSASSA-PSS vs. PKCS1-v1_5 and the hash algorithm when signing a PDF. Chilkat2 Java

import com.chilkatsoft.chilkat2.Cert;
import com.chilkatsoft.chilkat2.ChilkatException;
import com.chilkatsoft.chilkat2.JsonObject;
import com.chilkatsoft.chilkat2.Pdf;

public class ChilkatExample {

    public static void main(String[] args) {
        // This example requires the Chilkat API to have been previously unlocked.
        // See Global Unlock Sample for sample code.

        Pdf pdf = new Pdf();

        // Load a PDF to be signed.
        // The "hello.pdf" is available at https://chilkatsoft.com/hello.pdf
        try {
            pdf.loadFile("qa_data/pdf/hello.pdf");
        } catch (ChilkatException e) {
            System.out.println(e.getLastErrorText());
            return;
        }

        // Options for signing are specified in JSON.
        JsonObject json = new 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 cert = new Cert();
        try {
            cert.loadPfxFile("qa_data/pfx/myPdfSigningCert.pfx", "secret");

            // Tell the pdf object to use the certificate for signing.
            pdf.setSigningCert(cert);

            pdf.signPdf(json, "qa_output/hello_signed.pdf");
        } catch (ChilkatException e) {
            System.out.println(e.getLastErrorText());
            return;
        }

        System.out.println("The PDF has been successfully cryptographically signed.");

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

        // 
    }
}