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
>
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Cumprimentos,
Gonçalo Almeida
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