(C) 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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#include <C_CkPdf.h>
#include <C_CkJsonObject.h>
#include <C_CkCert.h>

void ChilkatSample(void)
    {
    HCkPdf pdf;
    BOOL success;
    HCkJsonObject json;
    HCkCert cert;

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

    pdf = CkPdf_Create();

    // Load a PDF to be signed.
    // The "hello.pdf" is available at https://chilkatsoft.com/hello.pdf
    success = CkPdf_LoadFile(pdf,"qa_data/pdf/hello.pdf");
    if (success == FALSE) {
        printf("%s\n",CkPdf_lastErrorText(pdf));
        CkPdf_Dispose(pdf);
        return;
    }

    // Options for signing are specified in JSON.
    json = CkJsonObject_Create();

    // In most cases, the signingCertificateV2 attribute is needed.
    CkJsonObject_UpdateInt(json,"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.)
    CkJsonObject_UpdateString(json,"hashAlgorithm","sha256");

    // To choose PKCSV1_5:
    CkJsonObject_UpdateString(json,"signingAlgorithm","pkcs");
    // Alternatively, to choose RSASSA-PSS:
    CkJsonObject_UpdateString(json,"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
    CkJsonObject_UpdateInt(json,"page",1);
    CkJsonObject_UpdateString(json,"appearance.y","top");
    CkJsonObject_UpdateString(json,"appearance.x","left");

    // Use a font scale of 10.0
    CkJsonObject_UpdateString(json,"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.
    CkJsonObject_UpdateString(json,"appearance.text[0]","Digitally signed by: cert_cn");
    CkJsonObject_UpdateString(json,"appearance.text[1]","current_dt");
    CkJsonObject_UpdateString(json,"appearance.text[2]","The crazy brown fox jumps over the lazy dog.");

    // Load the signing certificate. (Use your own certificate.)
    cert = CkCert_Create();
    success = CkCert_LoadPfxFile(cert,"qa_data/pfx/myPdfSigningCert.pfx","secret");
    if (success == FALSE) {
        printf("%s\n",CkCert_lastErrorText(cert));
        CkPdf_Dispose(pdf);
        CkJsonObject_Dispose(json);
        CkCert_Dispose(cert);
        return;
    }

    // Tell the pdf object to use the certificate for signing.
    success = CkPdf_SetSigningCert(pdf,cert);
    if (success == FALSE) {
        printf("%s\n",CkPdf_lastErrorText(pdf));
        CkPdf_Dispose(pdf);
        CkJsonObject_Dispose(json);
        CkCert_Dispose(cert);
        return;
    }

    success = CkPdf_SignPdf(pdf,json,"qa_output/hello_signed.pdf");
    if (success == FALSE) {
        printf("%s\n",CkPdf_lastErrorText(pdf));
        CkPdf_Dispose(pdf);
        CkJsonObject_Dispose(json);
        CkCert_Dispose(cert);
        return;
    }

    printf("The PDF has been successfully cryptographically signed.\n");

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

    


    CkPdf_Dispose(pdf);
    CkJsonObject_Dispose(json);
    CkCert_Dispose(cert);

    }