Zig

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. Zig

const std = @import("std");
const chilkat = @import("chilkat");

pub fn main(init: std.process.Init) !void {
    const alloc = init.arena.allocator();

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

    const pdf = try chilkat.Pdf.init();
    defer pdf.deinit();

    // Load a PDF to be signed.
    // The "hello.pdf" is available at https://chilkatsoft.com/hello.pdf
    pdf.loadFile("qa_data/pdf/hello.pdf") catch {
        std.debug.print("{s}\n", .{try pdf.getLastErrorText(alloc)});
        return;
    };

    // Options for signing are specified in JSON.
    const json = try chilkat.JsonObject.init();
    defer json.deinit();

    // In most cases, the signingCertificateV2 attribute is needed.
    json.updateInt("signingCertificateV2", 1) catch {};

    // ---------------------------------------------------------------------------------------------------------------------------
    // 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") catch {};

    // To choose PKCSV1_5:
    json.updateString("signingAlgorithm", "pkcs") catch {};
    // Alternatively, to choose RSASSA-PSS:
    json.updateString("signingAlgorithm", "pss") catch {};

    // 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) catch {};
    json.updateString("appearance.y", "top") catch {};
    json.updateString("appearance.x", "left") catch {};

    // Use a font scale of 10.0
    json.updateString("appearance.fontScale", "10.0") catch {};

    // 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") catch {};
    json.updateString("appearance.text[1]", "current_dt") catch {};
    json.updateString("appearance.text[2]", "The crazy brown fox jumps over the lazy dog.") catch {};

    // Load the signing certificate. (Use your own certificate.)
    const cert = try chilkat.Cert.init();
    defer cert.deinit();
    cert.loadPfxFile("qa_data/pfx/myPdfSigningCert.pfx", "secret") catch {
        std.debug.print("{s}\n", .{try cert.getLastErrorText(alloc)});
        return;
    };

    // Tell the pdf object to use the certificate for signing.
    pdf.setSigningCert(cert) catch {
        std.debug.print("{s}\n", .{try pdf.getLastErrorText(alloc)});
        return;
    };

    pdf.signPdf(json, "qa_output/hello_signed.pdf") catch {
        std.debug.print("{s}\n", .{try pdf.getLastErrorText(alloc)});
        return;
    };

    std.debug.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)
}