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

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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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VBScript 
Dim fso, outFile
Set fso = CreateObject("Scripting.FileSystemObject")
'Create a Unicode (utf-16) output text file.
Set outFile = fso.CreateTextFile("output.txt", True, True)

success = 0

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

set pdf = CreateObject("Chilkat.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 = 0) Then
    outFile.WriteLine(pdf.LastErrorText)
    WScript.Quit
End If

'  Options for signing are specified in JSON.
set json = CreateObject("Chilkat.JsonObject")

'  In most cases, the signingCertificateV2 attribute is needed.
success = 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.)
success = json.UpdateString("hashAlgorithm","sha256")

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

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

'  Load the signing certificate. (Use your own certificate.)
set cert = CreateObject("Chilkat.Cert")
success = cert.LoadPfxFile("qa_data/pfx/myPdfSigningCert.pfx","secret")
If (success = 0) Then
    outFile.WriteLine(cert.LastErrorText)
    WScript.Quit
End If

'  Tell the pdf object to use the certificate for signing.
success = pdf.SetSigningCert(cert)
If (success = 0) Then
    outFile.WriteLine(pdf.LastErrorText)
    WScript.Quit
End If

success = pdf.SignPdf(json,"qa_output/hello_signed.pdf")
If (success = 0) Then
    outFile.WriteLine(pdf.LastErrorText)
    WScript.Quit
End If

outFile.WriteLine("The PDF has been successfully cryptographically signed.")

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

'  image

outFile.Close