ClientSideSigning.cs

using System;
using System.Collections.Generic;
using System.IO;
using iTextSharp.text;
using iTextSharp.text.pdf;
using iTextSharp.text.pdf.security;
using NUnit.Framework;
using Org.BouncyCastle.Crypto;
using Org.BouncyCastle.Pkcs;
using Org.BouncyCastle.Security;
using Org.BouncyCastle.X509;

namespace itextsharp.tests.iTextSharp.text.signature
{
	[TestFixture]
	public class ClientSignatureTest
	{
		public const string KEYSTORE = @"..\..\resources\text\pdf\signature\ds-ks\ot.pfx";
		public const string KEYSTORE_PUB = @"..\..\resources\text\pdf\signature\ds-ks\ot_pub.cer";
		// public const String KEYSTORE = @"..\..\resources\text\pdf\signature\ds-ks\cert2.pfx";
		public const string PASSWORD = "password";
		// public const String Src = @"..\..\resources\text\pdf\signature\xfa.pdf";
		public const string Src =
			@"D:\projectsgit\iTextSharp\src\extras\itextsharp.tests\resources\text\pdf\signature\grusho.pdf";

		public const string Dst =
			@"D:\projectsgit\iTextSharp\src\extras\itextsharp.tests\resources\text\pdf\signature\grusho.signed.pdf";

		public const string Dst2 =
			@"D:\projectsgit\iTextSharp\src\extras\itextsharp.tests\resources\text\pdf\signature\grusho.signed2.pdf";

		public const string CmpDir = @"..\..\resources\text\pdf\signature\ds-ks\";
		public const string DestDir = @"signatures\ds-ks\";

		public const string HashAlg = "SHA1";
		public const string SignAlg = "SHA-1withRSA";

		private class SignatureDTO
		{
			public byte[] AuthenticatedAttributeBytes { get; set; }
			public byte[] Hash { get; set; }
			public PdfSignatureAppearance SignatureAppearance { get; set; }
			public PdfPKCS7 Sign { get; set; }
			public DateTime Now { get; set; }
			public Stream Stream { get; set; }
		}

		private AsymmetricKeyEntry LoadCertificateChainFromKeyStorage()
		{
			MemoryStream ks = new MemoryStream();
			using (FileStream reader = new FileStream(KEYSTORE, FileMode.Open))
			{
				byte[] buffer = new byte[reader.Length];
				reader.Read(buffer, 0, (int)reader.Length);
				ks.Write(buffer, 0, buffer.Length);
				ks.Position = 0;
			}
			Pkcs12Store store = new Pkcs12Store(ks, PASSWORD.ToCharArray());
			String alias = "";
			List<X509Certificate> chain = new List<X509Certificate>();
			// searching for private key

			foreach (string al in store.Aliases)
			{
				if (store.IsKeyEntry(al) && store.GetKey(al).Key.IsPrivate)
				{
					alias = al;
					break;
				}
			}

			foreach (X509CertificateEntry c in store.GetCertificateChain(alias)) // may be return too
				chain.Add(c.Certificate);

			AsymmetricKeyEntry pk = store.GetKey(alias);
			return pk;
			//return chain;
		}

		[Test]
		public void SignTest()
		{
			SignatureDTO result = ServerSidePrepare();
			byte[] signedData = ClientSideSign(result.AuthenticatedAttributeBytes);
			SaveSignedDocumentOnServer(result, signedData);
		}

		private SignatureDTO ServerSidePrepare()
		{
			// get public key chain
			X509Certificate cert = new X509CertificateParser().ReadCertificate(
				File.ReadAllBytes(KEYSTORE_PUB)); // сервер у нас и так имеет публичный ключ пользователя

			PdfReader reader = new PdfReader(Src); // считаем что файл перед подписью есть на сервере
			// MemoryStream ms = new MemoryStream();
			// var ms = File.Create(Dst);
			FileStream os = new FileStream(Dst, FileMode.Create);
			PdfStamper stamper = PdfStamper.CreateSignature(reader, os, '\0');

			PdfSignatureAppearance sap = stamper.SignatureAppearance;
			sap.Reason = "reason";
			sap.Location = "location";
			sap.Certificate = cert;

			sap.SetVisibleSignature(new Rectangle(36, 748, 144, 780), 1, "sig");

			PdfSignature dic = new PdfSignature(PdfName.ADOBE_PPKLITE, PdfName.ADBE_PKCS7_DETACHED);

			dic.Reason = sap.Reason;
			dic.Location = sap.Location;
			dic.Contact = sap.Contact;
			// dic.Date = new PdfDate(sap.SignDate);
			dic.Date = new PdfDate(new DateTime(2015, 7, 26, 17, 5, 25));

			sap.CryptoDictionary = dic;

			Dictionary<PdfName, int> exc = new Dictionary<PdfName, int>
			{
				{ PdfName.CONTENTS, 8192 * 2 + 2 }
				// не подписываемые данные (исключения). Зависит от того, внедрены ли CRL и ответы OCSP в документе.
				// PdfName.CONTENTS здесь должен быть обязательно 
			};

			sap.PreClose(exc);

			var sgn = new PdfPKCS7(null, new[] { cert }, HashAlg, false);

			Stream data = sap.GetRangeStream();
			// byte[] hash = DigestAlgorithms.Digest(data, externalDigest.getMessageDigest("SHA256"));
			byte[] messageHash = DigestAlgorithms.Digest(data, HashAlg); // hash calculated. Sending it to client.
			var now = DateTime.Now;
			return new SignatureDTO
			{
				Hash = messageHash,
				AuthenticatedAttributeBytes = sgn.getAuthenticatedAttributeBytes(messageHash, now, null, null, CryptoStandard.CMS),
				Now = now,
				SignatureAppearance = sap,
				Sign = sgn,
				Stream = os
			};
		}

		private byte[] ClientSideSign(byte[] hash)
		{
			AsymmetricKeyEntry pk = LoadCertificateChainFromKeyStorage();

			// we sign the hash received from the server
			ISigner sig = SignerUtilities.GetSigner(SignAlg);
			sig.Init(true, pk.Key);
			sig.BlockUpdate(hash, 0, hash.Length);
			return sig.GenerateSignature();
		}

		private void SaveSignedDocumentOnServer(SignatureDTO result, byte[] signature)
		{
			result.Sign.SetExternalDigest(signature, null, "RSA");
			byte[] encodedSig = result.Sign.GetEncodedPKCS7(result.Hash, result.Now, null, null, null, CryptoStandard.CMS);

			byte[] paddedSig = new byte[8192];
			Array.Copy(encodedSig, 0, paddedSig, 0, encodedSig.Length);

			PdfDictionary pdfDic = new PdfDictionary();
			pdfDic.Put(PdfName.CONTENTS, new PdfString(paddedSig).SetHexWriting(true));

			result.SignatureAppearance.Close(pdfDic); // use try/catch in real app
		}
	}
}