(CkPython) 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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import sys
import chilkat

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

pdf = chilkat.CkPdf()

# 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):
    print(pdf.lastErrorText())
    sys.exit()

# Options for signing are specified in JSON.
json = chilkat.CkJsonObject()

# 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.)
cert = chilkat.CkCert()
success = cert.LoadPfxFile("qa_data/pfx/myPdfSigningCert.pfx","secret")
if (success == False):
    print(cert.lastErrorText())
    sys.exit()

# Tell the pdf object to use the certificate for signing.
success = pdf.SetSigningCert(cert)
if (success == False):
    print(pdf.lastErrorText())
    sys.exit()

success = pdf.SignPdf(json,"qa_output/hello_signed.pdf")
if (success == False):
    print(pdf.lastErrorText())
    sys.exit()

print("The PDF has been successfully cryptographically signed.")

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