Visual FoxPro

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. Visual FoxPro

LOCAL lnSuccess
LOCAL loPdf
LOCAL loJson
LOCAL loCert

lnSuccess = 0

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

loPdf = CreateObject('Chilkat.Pdf')

* Load a PDF to be signed.
* The "hello.pdf" is available at https://chilkatsoft.com/hello.pdf
lnSuccess = loPdf.LoadFile("qa_data/pdf/hello.pdf")
IF (lnSuccess = 0) THEN
    ? loPdf.LastErrorText
    RELEASE loPdf
    CANCEL
ENDIF

* Options for signing are specified in JSON.
loJson = CreateObject('Chilkat.JsonObject')

* In most cases, the signingCertificateV2 attribute is needed.
loJson.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.)
loJson.UpdateString("hashAlgorithm","sha256")

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

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

* Load the signing certificate. (Use your own certificate.)
loCert = CreateObject('Chilkat.Cert')
lnSuccess = loCert.LoadPfxFile("qa_data/pfx/myPdfSigningCert.pfx","secret")
IF (lnSuccess = 0) THEN
    ? loCert.LastErrorText
    RELEASE loPdf
    RELEASE loJson
    RELEASE loCert
    CANCEL
ENDIF

* Tell the pdf object to use the certificate for signing.
lnSuccess = loPdf.SetSigningCert(loCert)
IF (lnSuccess = 0) THEN
    ? loPdf.LastErrorText
    RELEASE loPdf
    RELEASE loJson
    RELEASE loCert
    CANCEL
ENDIF

lnSuccess = loPdf.SignPdf(loJson,"qa_output/hello_signed.pdf")
IF (lnSuccess = 0) THEN
    ? loPdf.LastErrorText
    RELEASE loPdf
    RELEASE loJson
    RELEASE loCert
    CANCEL
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)

RELEASE loPdf
RELEASE loJson
RELEASE loCert