It's not posible to predict the signature size. Sign twice, the first time to know the size.
Paulo ----- Original Message ----- From: "Armin Häberling" <[EMAIL PROTECTED]> To: <itext-questions@lists.sourceforge.net> Sent: Monday, December 11, 2006 5:08 PM Subject: [iText-questions] computing the signature size before signing? > Hi, > > Is there a convenience way to compute the size needed for an external > signature, prior to signing? > To clarify my question. The following is an example from > http://itextpdf.sourceforge.net/howtosign.html, which shows how an > external signature is added to a pdf. > >> KeyStore ks = KeyStore.getInstance("pkcs12"); >> ks.load(new FileInputStream("my_private_key.pfx"), >> "my_password".toCharArray()); >> String alias = (String)ks.aliases().nextElement(); >> PrivateKey key = (PrivateKey)ks.getKey(alias, "password".toCharArray()); >> Certificate[] chain = ks.getCertificateChain(alias); >> >> PdfReader reader = new PdfReader("original.pdf"); >> FileOutputStream fout = new FileOutputStream("signed.pdf"); >> PdfStamper stp = PdfStamper.createSignature(reader, fout, '\0'); >> PdfSignatureAppearance sap = stp.getSignatureAppearance(); >> // comment next line to have an invisible signature >> sap.setVisibleSignature(new Rectangle(100, 100, 200, 200), 1, null); >> sap.setLayer2Text("This is some custom made text.\n\nDate: some date"); >> Calendar cal = Calendar.getInstance(); >> PdfDictionary dic = new PdfDictionary(); >> dic.put(PdfName.FT, PdfName.SIG); >> dic.put(PdfName.FILTER, new PdfName("SAFE.PPKSF")); >> dic.put(PdfName.SUBFILTER, new PdfName("adbe.pkcs7.detached")); >> dic.put(PdfName.M, new PdfDate(cal)); >> dic.put(PdfName.NAME, new >> PdfString(PdfPKCS7.getSubjectFields((X509Certificate)chain[0]).getField("CN"))); >> sap.setCryptoDictionary(dic); >> HashMap exc = new HashMap(); > >> exc.put(PdfName.CONTENTS, new Integer(0x2502)); > > here we save space for the signature. the size of the signature is > hardcoded in this example. my question is how do I compute this size > prior to generating the signature? > >> sap.preClose(exc); >> >> PdfPKCS7 pk7 = new PdfPKCS7(key, chain, null, "SHA1", null, false); >> MessageDigest messageDigest = MessageDigest.getInstance("SHA1"); >> byte buf[] = new byte[8192]; >> int n; >> InputStream inp = sap.getRangeStream(); >> while ((n = inp.read(buf)) > 0) { >> messageDigest.update(buf, 0, n); >> } >> byte hash[] = messageDigest.digest(); >> byte sh[] = pk7.getAuthenticatedAttributeBytes(hash, cal); >> pk7.update(sh, 0, sh.length); >> PdfDictionary dic2 = new PdfDictionary(); >> byte sg[] = pk7.getEncodedPKCS7(hash, cal); >> byte out[] = new byte[0x2500 / 2]; >> System.arraycopy(sg, 0, out, 0, sg.length); >> dic2.put(PdfName.CONTENTS, new PdfString(out).setHexWriting(true)); >> sap.close(dic2); > > Thanks in advance. > > Regards, > Armin > > ------------------------------------------------------------------------- > Take Surveys. Earn Cash. Influence the Future of IT > Join SourceForge.net's Techsay panel and you'll get the chance to share > your > opinions on IT & business topics through brief surveys - and earn cash > http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV > _______________________________________________ > iText-questions mailing list > iText-questions@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/itext-questions > Buy the iText book: http://itext.ugent.be/itext-in-action/ ------------------------------------------------------------------------- Take Surveys. Earn Cash. Influence the Future of IT Join SourceForge.net's Techsay panel and you'll get the chance to share your opinions on IT & business topics through brief surveys - and earn cash http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV _______________________________________________ iText-questions mailing list iText-questions@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/itext-questions Buy the iText book: http://itext.ugent.be/itext-in-action/
