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WORKSHOP
Electronic signature of PDF documents
the Adobe Acrobat software supports a number of standards for electronic
signatures, especially the PKCS de facto standards.the best way to establish
that a PDf document is authentic and genuine is to check whether the
digital signatures (if any) within it are authentic. A PDf document can have
two kinds of digital signatures.
• A certiication signature, which can be applied by the document’s author:
Adobe Reader or Acrobat automatically checks the authenticity of this
signature when one opens the document, and then displays a window
that indicates whether the signature is valid (that is, authentic and current).
the certiication signature can be described as the ‘author’s digital signature’.
• A standard signature, which can be applied by anyone who has permission
to digitally sign the document: Adobe Reader or Acrobat can automatically
check the authenticity of standard signatures when one opens
the document, or one can check them manually from within the application.
(NB: Adobe Reader or Acrobat must have access to the Internet to
check digital signatures.)
CHECKING THE CERTIFICATION SIGNATURE FOR PDF DOCUMENTS
Immediately after a certiied Adobe PDf document is opened, Adobe
Reader or Acrobat automatically checks for unauthorised modiications to the
document and checks the authenticity of the certiication signature. the software
then opens a document status window that shows one of three results:
‘Certiication valid’, with a blue ribbon; ‘Validation of author not conirmed’,
with a blue question mark next to a person; or ‘Certiication invalid’, with a red
X. A valid result can provide strong assurance that the document has not been
modiied and that the document is genuine.
Challenges in the use of electronic signatures
there are several challenges in the use of electronic signatures. the irst
challenge is in the choice of the most suitable signature. there are several alternatives
and each of them has a different procedure for utilisation.
the second challenge is that electronic signatures are ageing. Increasing
computing power, the possibility of networking, and the progress of cryptography
contribute to the ‘weakening’ of electronic signatures, i.e. electronically
signed documents may lose their probative value over the years. Electronic
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