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Sign PDF using PAdES-T using multiple certificates at once

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#27035
Posted: 10/31/2013 04:49:19
by Petr Kykal (Standard support level)
Joined: 04/10/2013
Posts: 18

Hello,

I would like to know if it is possible to sign PDF document by multiple people (multiple certificates) and timestamp it at once?

I am trying to do it using
Code
m_SignCertStorage.Add(m_SignCert, true);
multiple times with different certificates and then I perform sign using the
Code
m_SignHandler.SetCertStorage(m_SignCertStorage);
method, with multiple certificates in the storage.

But the result is, that only the first certificate is used. The timestamp is present as expected.

Please could you provide me with a solution?
#27036
Posted: 10/31/2013 04:56:59
by Vsevolod Ievgiienko (EldoS Corp.)

Thank you for contacting us.

Its not possible. You should create each signature separately.
#27039
Posted: 10/31/2013 05:46:14
by Ken Ivanov (EldoS Corp.)

Petr,

No, and it is caused by a limitation of the PDF standard. While the underlying PKCS#7 format allows creation of multi-signer signatures, PDF/PAdES requires that each signature is created strictly by one signer.
#27042
Posted: 10/31/2013 06:53:16
by Petr Kykal (Standard support level)
Joined: 04/10/2013
Posts: 18

Thank you for your answers.

If I do it the way, that I Save the document after each signature and timestamp, does this mean, that the next signature invalidates the signature before it or not?

I need for example five valid signatures on a document with a proof of time the document was signed by them (using timestamp). All of the signers will do it right afer each other without any delay or document change.
#27043
Posted: 10/31/2013 07:02:03
by Ken Ivanov (EldoS Corp.)

Petr,

Each signature is added to the document in an incremental way (by appending the necessary changes to the end of the document), so it doesn't invalidate the preceding signatures. At the same time, each subsequent signature, along with the document, covers all the previously made signatures (i.e. the first signature covers the document, the second covers the document and the first signature, the third covers the document and the first two signatures and so on).
#27044
Posted: 10/31/2013 07:10:41
by Petr Kykal (Standard support level)
Joined: 04/10/2013
Posts: 18

Great,
thank you.
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