Tcl

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. Tcl

load ./chilkat.dll

set success 0

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

set pdf [new_CkPdf]

# Load a PDF to be signed.
# The "hello.pdf" is available at https://chilkatsoft.com/hello.pdf
set success [CkPdf_LoadFile $pdf "qa_data/pdf/hello.pdf"]
if {$success == 0} then {
    puts [CkPdf_lastErrorText $pdf]
    delete_CkPdf $pdf
    exit
}

# Options for signing are specified in JSON.
set json [new_CkJsonObject]

# In most cases, the signingCertificateV2 attribute is needed.
CkJsonObject_UpdateInt $json "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.)
CkJsonObject_UpdateString $json "hashAlgorithm" "sha256"

# To choose PKCSV1_5:
CkJsonObject_UpdateString $json "signingAlgorithm" "pkcs"
# Alternatively, to choose RSASSA-PSS:
CkJsonObject_UpdateString $json "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
CkJsonObject_UpdateInt $json "page" 1
CkJsonObject_UpdateString $json "appearance.y" "top"
CkJsonObject_UpdateString $json "appearance.x" "left"

# Use a font scale of 10.0
CkJsonObject_UpdateString $json "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.
CkJsonObject_UpdateString $json "appearance.text[0]" "Digitally signed by: cert_cn"
CkJsonObject_UpdateString $json "appearance.text[1]" "current_dt"
CkJsonObject_UpdateString $json "appearance.text[2]" "The crazy brown fox jumps over the lazy dog."

# Load the signing certificate. (Use your own certificate.)
set cert [new_CkCert]

set success [CkCert_LoadPfxFile $cert "qa_data/pfx/myPdfSigningCert.pfx" "secret"]
if {$success == 0} then {
    puts [CkCert_lastErrorText $cert]
    delete_CkPdf $pdf
    delete_CkJsonObject $json
    delete_CkCert $cert
    exit
}

# Tell the pdf object to use the certificate for signing.
set success [CkPdf_SetSigningCert $pdf $cert]
if {$success == 0} then {
    puts [CkPdf_lastErrorText $pdf]
    delete_CkPdf $pdf
    delete_CkJsonObject $json
    delete_CkCert $cert
    exit
}

set success [CkPdf_SignPdf $pdf $json "qa_output/hello_signed.pdf"]
if {$success == 0} then {
    puts [CkPdf_lastErrorText $pdf]
    delete_CkPdf $pdf
    delete_CkJsonObject $json
    delete_CkCert $cert
    exit
}

puts "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)

delete_CkPdf $pdf
delete_CkJsonObject $json
delete_CkCert $cert