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:

#  

delete_CkPdf $pdf
delete_CkJsonObject $json
delete_CkCert $cert