/**
* Signs a PDF where space was already reserved.
* @param reader the original PDF
* @param fieldName the field to sign. It must be the last field
* @param outs the output PDF
* @param externalSignatureContainer the signature container doing the actual signing. Only the
* method ExternalSignatureContainer.sign is used
* @throws DocumentException
* @throws IOException
* @throws GeneralSecurityException
*/
public static void SignDeferred(PdfReader reader, String fieldName, Stream outs, IExternalSignatureContainer externalSignatureContainer) {
AcroFields af = reader.AcroFields;
PdfDictionary v = af.GetSignatureDictionary(fieldName);
if (v == null)
throw new DocumentException("No field");
if (!af.SignatureCoversWholeDocument(fieldName))
throw new DocumentException("Not the last signature");
PdfArray b = v.GetAsArray(PdfName.BYTERANGE);
long[] gaps = b.AsLongArray();
if (b.Size != 4 || gaps[0] != 0)
throw new DocumentException("Single exclusion space supported");
IRandomAccessSource readerSource = reader.SafeFile.CreateSourceView();
Stream rg = new RASInputStream(new RandomAccessSourceFactory().CreateRanged(readerSource, gaps));
byte[] signedContent = externalSignatureContainer.Sign(rg);
int spaceAvailable = (int)(gaps[2] - gaps[1]) - 2;
if ((spaceAvailable & 1) != 0)
throw new DocumentException("Gap is not a multiple of 2");
spaceAvailable /= 2;
if (spaceAvailable < signedContent.Length)
throw new DocumentException("Not enough space");
StreamUtil.CopyBytes(readerSource, 0, gaps[1] + 1, outs);
ByteBuffer bb = new ByteBuffer(spaceAvailable * 2);
foreach (byte bi in signedContent) {
bb.AppendHex(bi);
}
int remain = (spaceAvailable - signedContent.Length) * 2;
for (int k = 0; k < remain; ++k) {
bb.Append((byte)48);
}
bb.WriteTo(outs);
StreamUtil.CopyBytes(readerSource, gaps[2] - 1, gaps[3] + 1, outs);
}
private static String ConvertToHex(byte[] bt)
{
ByteBuffer buf = new ByteBuffer();
foreach (byte b in bt) {
buf.AppendHex(b);
}
return PdfEncodings.ConvertToString(buf.ToByteArray(), null).ToUpperInvariant();
}
