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

This example demonstrates how to choose between RSASSA-PSS vs. PKCS1-v1_5 and the hash algorithm when signing a PDF.
Chilkat Xbase++ Downloads

Xbase++
LOCAL nSuccess
LOCAL oPdf
LOCAL oJson
LOCAL oCert

nSuccess := 0

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

oPdf := CreateObject("Chilkat.Pdf")

//  Load a PDF to be signed.
//  The "hello.pdf" is available at https://chilkatsoft.com/hello.pdf
nSuccess := oPdf:LoadFile("qa_data/pdf/hello.pdf")
IF (nSuccess == 0)
    ? oPdf:LastErrorText
    oPdf:destroy()
    RETURN
ENDIF

//  Options for signing are specified in JSON.
oJson := CreateObject("Chilkat.JsonObject")

//  In most cases, the signingCertificateV2 attribute is needed.
oJson: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.)
oJson:UpdateString("hashAlgorithm", "sha256")

//  To choose PKCSV1_5:
oJson:UpdateString("signingAlgorithm", "pkcs")
//  Alternatively, to choose RSASSA-PSS:
oJson: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
oJson:UpdateInt("page", 1)
oJson:UpdateString("appearance.y", "top")
oJson:UpdateString("appearance.x", "left")

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

//  Load the signing certificate. (Use your own certificate.)
oCert := CreateObject("Chilkat.Cert")
nSuccess := oCert:LoadPfxFile("qa_data/pfx/myPdfSigningCert.pfx", "secret")
IF (nSuccess == 0)
    ? oCert:LastErrorText
    oPdf:destroy()
    oJson:destroy()
    oCert:destroy()
    RETURN
ENDIF

//  Tell the pdf object to use the certificate for signing.
nSuccess := oPdf:SetSigningCert(oCert)
IF (nSuccess == 0)
    ? oPdf:LastErrorText
    oPdf:destroy()
    oJson:destroy()
    oCert:destroy()
    RETURN
ENDIF

nSuccess := oPdf:SignPdf(oJson, "qa_output/hello_signed.pdf")
IF (nSuccess == 0)
    ? oPdf:LastErrorText
    oPdf:destroy()
    oJson:destroy()
    oCert:destroy()
    RETURN
ENDIF

? "The PDF has been successfully cryptographically signed."

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

//  (image:https://example-code.com/images/signature1.jpg/endImage)

oPdf:destroy()
oJson:destroy()
oCert:destroy()