Hi all,
I'm trying to use the samples in the tutorial for using external
signature in Self Sign Mode. It compiles ok, but when I verify it, it
always says it has been modified.
The code I'm using is:
public static void signPDF()
{
try
{
KeyStore ks = KeyStore.getInstance(KeyStore.getDefaultType());
ks.load(new FileInputStream("c:\\Downloads\\keystore.ks"),
"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("c:\\original.pdf");
FileOutputStream fout = new FileOutputStream("c:\\signed.pdf");
PdfStamper stp = PdfStamper.createSignature(reader, fout, '\0');
PdfSignatureAppearance sap = stp.getSignatureAppearance();
sap.setCrypto(key, chain, null,
PdfSignatureAppearance.SELF_SIGNED);
sap.setReason("Testing");
sap.setLocation("Sao Paulo");
sap.setExternalDigest(new byte[128], null, "RSA");
sap.preClose();
PdfPKCS7 sig =
sap.getSigStandard().getSigner();
Signature sign = Signature.getInstance("SHA1withRSA");
sign.initSign(key);
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[] signature = sign.sign();
String base64 = Conversion.byteArrayToBase64String(signature);
sig.setExternalDigest(signature, null, "RSA");
PdfDictionary dic = new PdfDictionary();
dic.put(PdfName.CONTENTS, new
PdfString(sig.getEncodedPKCS1()).setHexWriting(true));
// comment next line to have an invisible signature
sap.setVisibleSignature(new Rectangle(100, 100, 200, 200), 1,
null);
PdfTemplate n1 = sap.getLayer(1); //get rid of the question mark
PdfTemplate n2 = sap.getLayer(2);
n2.beginText();
BaseFont bf = BaseFont.createFont(BaseFont.HELVETICA,
BaseFont.CP1252, BaseFont.NOT_EMBEDDED);
n2.setFontAndSize(bf, 7);
n2.setLeading(2);
n2.showText("Signature:");
n2.setLeading(2);
n2.newlineShowText(base64);
n2.endText();
sap.close(dic);
}
catch (Exception e)
{
e.printStackTrace();
}
}
public static void checkPDF()
{
try
{ CertificateFactory cf =
CertificateFactory.getInstance("X509");
Collection col = cf.generateCertificates(new
FileInputStream("C:\\Downloads\\export.cer"));
KeyStore kall = KeyStore.getInstance(KeyStore.getDefaultType());
kall.load(null, null);
for (Iterator it = col.iterator(); it.hasNext();) {
X509Certificate cert = (X509Certificate)it.next();
kall.setCertificateEntry(cert.getSerialNumber().toString(Character.MAX_RADIX),
cert);
}
PdfReader reader = new PdfReader("c:\\signed.pdf");
AcroFields af = reader.getAcroFields();
ArrayList names = af.getSignatureNames();
for (int k = 0; k < names.size(); ++k) {
String name = (String)names.get(k);
System.out.println("Signature name: " + name);
System.out.println("Signature covers whole document: " +
af.signatureCoversWholeDocument(name));
System.out.println("Document revision: " +
af.getRevision(name) + " of " + af.getTotalRevisions());
// Start revision extraction
FileOutputStream out = new
FileOutputStream("c:\\revision_" + af.getRevision(name) + ".pdf");
byte bb[] = new byte[8192];
InputStream ip = af.extractRevision(name);
int n = 0;
while ((n = ip.read(bb)) > 0)
out.write(bb, 0, n);
out.close();
ip.close();
// End revision extraction
PdfPKCS7 pk = af.verifySignature(name);
Calendar cal = pk.getSignDate();
Certificate pkc[] = pk.getCertificates();
System.out.println("Subject: " +
PdfPKCS7.getSubjectFields(pk.getSigningCertificate()));
System.out.println("Document modified: " + !pk.verify());
Object fails[] = PdfPKCS7.verifyCertificates(pkc, kall,
null, cal);
if (fails == null)
System.out.println("Certificates verified against the
KeyStore");
else
System.out.println("Certificate failed: " + fails[1]);
}
}
catch (Exception e)
{
e.printStackTrace();
}
}
I thought it could be the fact that I'm trying to insert some text in
the Layer2 of the signature, so I commented it, but the result was the
same.
Does anybody have a clue on why it always detects a modification that
does not exist?
Any help would be greatly appreciated.
Thanks in advance,
Luiz Kobayashi
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