我正在编写一个概念验证证明，以便为现有PDF添加电子签名。我遇到了一个我无法解决的奇怪问题。似乎将签名添加到某些文档中工作正常，而向其他文档添加签名不起作用，并且生成了Adobe Reader无法打开的损坏文件。
这是我的代码：
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using iText;
using iText.Kernel.Pdf;
using System.IO;
using iText.Layout;
using iText.Layout.Element;
using iText.Kernel.Geom;
using Org.BouncyCastle.Crypto.Tls;
using iText.Signatures;
using System.Collections.ObjectModel;
using Org.BouncyCastle.Pkcs;
using System.Security.Cryptography.X509Certificates;
using Org.BouncyCastle.Crypto;
using System.Security.Cryptography;
using Org.BouncyCastle.Crypto.Parameters;
using Org.BouncyCastle.Math;
using iText.IO.Image;
namespace LTVSkilrikjaDemo
{
class Program
{
static void Main(string[] args)
{
string welcomeText = "Welcome to LTVSkilríkjaDemotolid!";
string pressEnterToTry = "Commands: 's' - sign, 'stop' - stops the programme";
Console.WriteLine(welcomeText);
Console.WriteLine(pressEnterToTry);
// Base directory prepared
string basedir = AppDomain.CurrentDomain.BaseDirectory;
int index = basedir.IndexOf(@"bin\");
basedir = basedir.Remove(index);
string readString = Console.ReadLine().ToLower();
while(!readString.Equals("stop"))
{
if(readString.Equals("c"))
{
string inFile = "Infile2.pdf";
string outFile = "Outfile2.pdf";
// Open PDF document and decide where to write the new document
PdfWorker worker = new PdfWorker();
worker.ReadPdf(basedir + "App_Data\\InFiles\\" + inFile, basedir + "App_Data\\OutFiles\\" + outFile);
// Start working on certificate
X509Store store = new X509Store("My");
store.Open(OpenFlags.ReadOnly);
Collection<Org.BouncyCastle.X509.X509Certificate> xcertificates = new Collection<Org.BouncyCastle.X509.X509Certificate>();
foreach (X509Certificate2 mCert in store.Certificates)
{
if (mCert.Subject.IndexOf("CN=Róbert") > -1)
{
xcertificates.Add(Org.BouncyCastle.Security.DotNetUtilities.FromX509Certificate(mCert));
}
}
Org.BouncyCastle.X509.X509Certificate[] certificatesProcessed = new Org.BouncyCastle.X509.X509Certificate[xcertificates.Count];
for(int i = 0; i < xcertificates.Count; i++)
{
certificatesProcessed[i] = xcertificates[i];
}
var pk = Org.BouncyCastle.Security.DotNetUtilities.GetKeyPair(store.Certificates[5].PrivateKey).Private;
try
{
worker.Sign(certificatesProcessed, pk, DigestAlgorithms.SHA1, PdfSigner.CryptoStandard.CADES, "No apparent raisin!", "Lost in Iceland", null, null, null, 0, true, basedir);
}
catch(Exception ex)
{
Console.ForegroundColor = ConsoleColor.Red;
Console.WriteLine("Error! " + ex.Message + "\n\r" + ex.StackTrace);
if(ex.InnerException != null)
{
Console.WriteLine("Inner exception: " + ex.InnerException.Message);
}
Console.ForegroundColor = ConsoleColor.Gray;
}
}
else if(!readString.Equals("stop"))
{
Console.WriteLine("Command not understood. Understand only 's' and 'stop'.");
}
readString = Console.ReadLine();
}
Console.WriteLine("Goodbye!");
System.Threading.Thread.Sleep(500);
}
}
public class PdfWorker
{
private PdfDocument _document;
private string _source;
private string _dest;
public void ReadPdf(string source, string dest)
{
_source = source;
_dest = dest;
}
public void Sign(Org.BouncyCastle.X509.X509Certificate[] chain, Org.BouncyCastle.Crypto.ICipherParameters pk,
string digestAlgorithm, PdfSigner.CryptoStandard subfilter, string reason,
string location, Collection<ICrlClient> crlList, IOcspClient ocspClient, ITSAClient tsaClient,
int estimatedSize, bool initial, string baseDir)
{
File.Copy(_source, _dest, true);
FileStream f = new FileStream(_dest, FileMode.Append);
try
{
PdfSigner signer = new PdfSigner(new PdfReader(_source), f, true);
_document = signer.GetDocument();
_document.AddNewPage();
// Work the last page
Rectangle pageSize = _document.GetLastPage().GetPageSizeWithRotation();
//PdfWriter w = _document.GetWriter();
//long currentPos = w.GetCurrentPos();
float llx = pageSize.GetWidth() - 350 - 20; //pageSize.GetWidth() / 2 - 350 / 2;
float lly = pageSize.GetHeight() - 50 - 20; // pageSize.GetHeight() / 2 - 150 / 2;
float urx = 350; //llx + 350;
float ury = 50; //lly + 150;
PdfSignatureAppearance appearance = signer.GetSignatureAppearance();
appearance.SetPageRect(new Rectangle(llx, lly, urx, ury));
appearance.SetReason(reason);
appearance.SetLocation(location);
byte[] imagebytes = File.ReadAllBytes(baseDir + "App_Data\\UndirskriftDemo.png");
// It is not possible to use the path as it contains Icelandic characters
// which itext chokes on. We use byte array instead
ImageData imgData = ImageDataFactory.Create(imagebytes);
Image img = new Image(imgData);
img = img.ScaleToFit(350.0f, 50.0f);
appearance.SetImage(imgData);
int pageCount = _document.GetNumberOfPages();
// Creating the appearance
if(initial == true)
{
signer.SetCertificationLevel(PdfSigner.CERTIFIED_FORM_FILLING_AND_ANNOTATIONS);
}
appearance.SetPageNumber(pageCount);
Rectangle rect = new Rectangle(10, 50, 350, 50);
appearance.SetPageRect(rect).SetPageNumber(pageCount);
appearance.SetRenderingMode(PdfSignatureAppearance.RenderingMode.NAME_AND_DESCRIPTION);
signer.SetFieldName(signer.GetNewSigFieldName());
// Creating the signature
IExternalSignature pks = new PrivateKeySignature(pk, digestAlgorithm);
signer.SignDetached(pks, chain, crlList, ocspClient, tsaClient, estimatedSize, subfilter);
Console.WriteLine("Signing successful!");
}
catch(Exception ex)
{
throw ex;
}
finally
{
_document.Close();
f.Close();
}
}
}
}
请在此处查看文档。 Infile1.pdf我无法签名，但Infile2.pdf签名正常。 Outfile1.pdf是损坏的文件。 https://app.box.com/s/52jqe8qirl80km6hunxucs00dntx70o5
是什么原因引起的？是否有关于输入PDF文件或上述程序的内容？
答案 0 :(得分：0)
问题在于您的程序，更确切地说是您的PdfWorker.Sign方法：
File.Copy(_source, _dest, true);
FileStream f = new FileStream(_dest, FileMode.Append);
try
{
PdfSigner signer = new PdfSigner(new PdfReader(_source), f, true);
...
首先复制文件以签名到目的地，然后将PdfSigner输出附加到其中。
但PdfSigner输出是完整的签名PDF，即源代码加上添加签名的附加修订版。因此，在目标文件中，您最终拥有两个源的副本，然后在假定只有一个源副本位于其前的情况下生成一些签名添加。
要解决此问题，只需删除File.Copy(_source, _dest, true)操作，不要使用FileStream打开FileMode.Append。
即使在此更正之后，签署OP的示例文件“Infile1.PDF”仍会创建一个损坏的PDF，同时签署示例文件“Infile2.pdf”现在成功。原因是this answer中解释的iText 7.0.0错误（据我所知）在7.0.1中得到修复。由于“Infile1.PDF”使用对象流而“Infile2.pdf”没有，因此只影响前一个文件。