Hi Antonio Mariano,
I've been facing the exact same problem here. Would you mind to share your
changes in iText source code, so that me and possibly others can implement
them?
Thank you very much in advance!
[]s, Renato Crivano
amarianoelaide wrote:
>
> Hi all,
> just a question about the hash computation.
>
> With reference to this code:
>
> PdfReader pdfReader = new PdfReader("/home/amariano/Desktop/sample.pdf");
> FileOutputStream PdfInMemory = new
> FileOutputStream("/home/amariano/Desktop/out.pdf");
> PdfStamper pdfStamper = PdfStamper.createSignature(pdfReader, PdfInMemory,
> '\0');
> PdfSignatureAppearance pdfSigApp = pdfStamper.getSignatureAppearance();
>
> PdfSignature sigDic = new PdfSignature(PdfName.ADOBE_PPKLITE,
> PdfName.ADBE_PKCS7_DETACHED);
> Calendar cal = Calendar.getInstance();
> cal.setTimeInMillis(new
> SimpleDateFormat("yyyyMMdd").parse("20090303").getTime());
> sigDic.setDate(new PdfDate(cal));
> sigDic.setReason("Pdf signature test");
> sigDic.setLocation("Italy");
> sigDic.setContact("Elaide S.r.l.");
> sigDic.setName("ACTestClient");
> pdfSigApp.setCryptoDictionary(sigDic);
> pdfSigApp.setAcro6Layers(true);
>
> HashMap<Object, Object> exclusions = new HashMap<Object, Object>();
> exclusions.put(PdfName.CONTENTS, new Integer(4000*2+2));
> pdfSigApp.preClose(exclusions);
>
> byte[] hash = getHash(pdfSigApp);
>
> System.out.println(new BASE64Encoder().encode(hash));
>
> where getHash is as following:
>
> public static byte[] getHash(PdfSignatureAppearance pdfSigApp) throws
> Exception
> {
> byte buf[] = new byte[8192];
> int n;
> InputStream inp = pdfSigApp.getRangeStream();
> MessageDigest messageDigest = MessageDigest.getInstance("SHA1");
>
> while ((n = inp.read(buf)) > 0)
> {
> messageDigest.update(buf, 0, n);
> }
> byte hash[] = messageDigest.digest();
>
> return hash;
> }
>
> if I run this code more than once I obtain different hash values.
> it's obvious that some "randomness" is introduced during successive hash
> computations.
> Is it possible to avoid it? And if yes how?
> If not, is it an IText peculiarity or is it a PDF hashing process issue?
> Hashing a normal file (text, binary, etc...) gives always the same hash
> value
>
> Thank you.
>
> Antonio Mariano
>
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