B4X
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.
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B4X
Dim success As Boolean = False

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

Dim pdf As ChilkatPdf
pdf.Initialize("pdf")

'  Load a PDF to be signed.
'  The "hello.pdf" is available at https://chilkatsoft.com/hello.pdf
success = pdf.LoadFile("qa_data/pdf/hello.pdf")
If success = False Then
    Log(pdf.LastErrorText)
    Return
End If


'  Options for signing are specified in JSON.
Dim json As ChilkatJsonObject
json.Initialize

'  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.)
Dim cert As ChilkatCert
cert.Initialize("cert")
success = cert.LoadPfxFile("qa_data/pfx/myPdfSigningCert.pfx", "secret")
If success = False Then
    Log(cert.LastErrorText)
    Return
End If


'  Tell the pdf object to use the certificate for signing.
success = pdf.SetSigningCert(cert)
If success = False Then
    Log(pdf.LastErrorText)
    Return
End If


success = pdf.SignPdf(json, "qa_output/hello_signed.pdf")
If success = False Then
    Log(pdf.LastErrorText)
    Return
End If


Log("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)