iTextSharp.text.pdf.security.MakeSignature.SignDetached C# (CSharp) Method

        public static void SignDetached(PdfSignatureAppearance sap, IExternalSignature externalSignature, ICollection<X509Certificate> chain, ICollection<ICrlClient> crlList, IOcspClient ocspClient,
            ITSAClient tsaClient, int estimatedSize, CryptoStandard sigtype)
        {
            List<X509Certificate> certa = new List<X509Certificate>(chain);
            ICollection<byte[]> crlBytes = null;
            int i = 0;
            while (crlBytes == null && i < certa.Count)
                crlBytes = ProcessCrl(certa[i++], crlList);
            if (estimatedSize == 0) {
                estimatedSize = 8192;
                if (crlBytes != null) {
                    foreach (byte[] element in crlBytes) {
                        estimatedSize += element.Length + 10;
                    }
                }
                if (ocspClient != null)
                    estimatedSize += 4192;
                if (tsaClient != null)
                    estimatedSize += 4192;
            }
            sap.Certificate = certa[0];
            PdfSignature dic = new PdfSignature(PdfName.ADOBE_PPKLITE, sigtype == CryptoStandard.CADES ? PdfName.ETSI_CADES_DETACHED : PdfName.ADBE_PKCS7_DETACHED);
            dic.Reason = sap.Reason;
            dic.Location = sap.Location;
            dic.Contact = sap.Contact;
            dic.Date = new PdfDate(sap.SignDate); // time-stamp will over-rule this
            sap.CryptoDictionary = dic;

            Dictionary<PdfName, int> exc = new Dictionary<PdfName, int>();
            exc[PdfName.CONTENTS] = estimatedSize * 2 + 2;
            sap.PreClose(exc);

            String hashAlgorithm = externalSignature.GetHashAlgorithm();
            PdfPKCS7 sgn = new PdfPKCS7(null, chain, hashAlgorithm, false);
            IDigest messageDigest = DigestUtilities.GetDigest(hashAlgorithm);
            Stream data = sap.GetRangeStream();
            byte[] hash = DigestAlgorithms.Digest(data, hashAlgorithm);
            DateTime cal = DateTime.Now;
            byte[] ocsp = null;
            if (chain.Count >= 2 && ocspClient != null) {
                ocsp = ocspClient.GetEncoded(certa[0], certa[1], null);
            }
            byte[] sh = sgn.getAuthenticatedAttributeBytes(hash, cal, ocsp, crlBytes, sigtype);
            byte[] extSignature = externalSignature.Sign(sh);
            sgn.SetExternalDigest(extSignature, null, externalSignature.GetEncryptionAlgorithm());

            byte[] encodedSig = sgn.GetEncodedPKCS7(hash, cal, tsaClient, ocsp, crlBytes, sigtype);

            if (estimatedSize + 2 < encodedSig.Length)
                throw new IOException("Not enough space");

            byte[] paddedSig = new byte[estimatedSize];
            System.Array.Copy(encodedSig, 0, paddedSig, 0, encodedSig.Length);

            PdfDictionary dic2 = new PdfDictionary();
            dic2.Put(PdfName.CONTENTS, new PdfString(paddedSig).SetHexWriting(true));
            sap.Close(dic2);
        }