Hi Gonçalo,
yes, simple replacing bytes within the PDF is easy, as I know the bytes that
build the signature. I wrote it myself as a placeholder.
Once the external sining process finished, I just replace bytes in a file. This
process doesn't require any knowledge about the file, this could work on any
file : Find byste 'xyz' and replace with '123'.
Greetings
Andreas
________________________________
From: Gonçalo Almeida <[email protected]>
To: Post all your questions about iText here
<[email protected]>
Sent: Tuesday, March 3, 2009 5:52:20 PM
Subject: Re: [iText-questions] signing pdf with external signature
Hello Andrea
I have a signed PDF and I want to change its signature.
You said it's quite easy, so I will ask you to give me an example.
I've tried to put the new signature bytes and I failed.
I've retrieved the PKCS7 from the PDF, changed the signature and then tried to
insert it in the same place the previous PKCS7 was. I failed.
Could you please show me some code?
Gonçalo
2009/2/10 Andreas Kuehne <[email protected]>
Hi,
here's code for extracting hash from signature :
// core aspect of PDF signatures :
// signatures are made by a special / partial hash
MessageDigest messageDigest = MessageDigest.getInstance(
getDocumentHashAlgorithm() );
byte read_buf[] = new byte[ hashBufferSize ];
int n;
InputStream inp = sap.getRangeStream();
while ( ( n = inp.read( read_buf ) ) > 0) {
messageDigest.update( read_buf, 0, n );
}
byte pdf_hash[] = messageDigest.digest();
Replacing the existing signature content is easy as I created it upfront with
well known content, big enough to hold the hex-coded signature. Once the
signature is ready, it's a simple find'n'replace method on the PDF file.
Greetings
Andreas
--
Andreas Kühne phone: +49 177 293 24 97 mailto: [email protected]
Trustable Ltd. Niederlassung Deutschland Ströverstr. 18 - 59427 Unna
Amtsgericht Hamm HRB 5868
Directors Andreas Kühne Heiko Veit
Company UK Company No: 5218868 Registered in England and Wales
------------------------------------------------------------------------------
Create and Deploy Rich Internet Apps outside the browser with Adobe(R)AIR(TM)
software. With Adobe AIR, Ajax developers can use existing skills and code to
build responsive, highly engaging applications that combine the power of local
resources and data with the reach of the web. Download the Adobe AIR SDK and
Ajax docs to start building applications today-http://p.sf.net/sfu/adobe-com
_______________________________________________
iText-questions mailing list
[email protected]
https://lists.sourceforge.net/lists/listinfo/itext-questions
Buy the iText book: http://www.1t3xt.com/docs/book.php
--
Cumprimentos,
Gonçalo Almeida
------------------------------------------------------------------------------
Open Source Business Conference (OSBC), March 24-25, 2009, San Francisco, CA
-OSBC tackles the biggest issue in open source: Open Sourcing the Enterprise
-Strategies to boost innovation and cut costs with open source participation
-Receive a $600 discount off the registration fee with the source code: SFAD
http://p.sf.net/sfu/XcvMzF8H
_______________________________________________
iText-questions mailing list
[email protected]
https://lists.sourceforge.net/lists/listinfo/itext-questions
Buy the iText book: http://www.1t3xt.com/docs/book.php
