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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