I created external digest using SetExternalDigest. But for some reason
PDF says "An error occured while attempting to validate this signature".
Here is what I do:
1) I calculate SHA1 hash from the PDF content (digest variable)
2) this hash is signed on the SmartCard and returned as rsadata
variable
public static void SignUsingMartCard(string filename, string outfile)
{
X509Certificate2 card = GetCertificate();
Org.BouncyCastle.X509.X509CertificateParser cp = new
Org.BouncyCastle.X509.X509CertificateParser();
Org.BouncyCastle.X509.X509Certificate[] chain = new
Org.BouncyCastle.X509.X509Certificate[] {
cp.ReadCertificate(card.RawData) };
PdfReader reader = new PdfReader(filename);
PdfStamper stp = PdfStamper.CreateSignature(reader, new
FileStream(outfile, FileMode.Create), '\0');
PdfSignatureAppearance sap = stp.SignatureAppearance;
sap.SetVisibleSignature(new Rectangle(100, 100, 300, 200),
1, null);
sap.SignDate = DateTime.Now;
sap.SetCrypto(null, chain, null, null);
sap.Reason = "I like to sign using C#";
sap.Location = "Universe";
sap.Acro6Layers = true;
sap.Render =
PdfSignatureAppearance.SignatureRender.NameAndDescription;
PdfSignature dic = new PdfSignature(PdfName.ADOBE_PPKLITE,
PdfName.ADBE_PKCS7_SHA1);
dic.Date = new PdfDate(sap.SignDate);
dic.Name =
PdfPKCS7.GetSubjectFields(chain[0]).GetField("CN");
if (sap.Reason != null)
dic.Reason = sap.Reason;
if (sap.Location != null)
dic.Location = sap.Location;
sap.CryptoDictionary = dic;
sap.SetExternalDigest(new byte[20], new byte[128], "SHA1");
int csize = 1280;
Hashtable exc = new Hashtable();
exc[PdfName.CONTENTS] = csize * 2 + 2;
sap.PreClose(exc);
Stream s = sap.RangeStream;
MemoryStream ss = new MemoryStream();
int read = 0;
byte[] buff = new byte[8192];
while ((read = s.Read(buff, 0, 8192)) > 0)
{
ss.Write(buff, 0, read);
}
// access SmartCard
// calculate SHA1 hash from ss.ToArray -> digest
// sign SHA1 hash -> rsadata
GetExternalBytes(ss.ToArray(), ref digest, ref rsadata);
PdfPKCS7 pk7 = new PdfPKCS7(null, chain, null, "SHA1",
false);
pk7.SetExternalDigest(digest, rsadata, "RSA");
byte[] pk = pk7.GetEncodedPKCS7();
byte[] outc = new byte[csize];
PdfDictionary dic2 = new PdfDictionary();
Array.Copy(pk, 0, outc, 0, pk.Length);
dic2.Put(PdfName.CONTENTS, new
PdfString(outc).SetHexWriting(true));
sap.Close(dic2);
}
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