使用iTextSharp将数字签名添加到PDF

Question

背景

我已经使用iTextSharp片刻了。 我创建了带有两个可签名的PdfFormFields的pdf文档。 如果我打开pdf文档，则可以手动签名每个字段。 我希望通过iTextSharp完成此操作。

我目前正在从X509Store检索证书。 到目前为止，我仍然可以弄清楚。

题

有人可以告诉我如何使用此X509Certificate2对已经存在的签名AcroField进行签名。

参考文献

访问了以下参考资料，但找不到所需的答案。 签署pdf文件

我相信这个链接离我最近了，但是所使用的几行无效，我不知道是否可以通过包含一些其他库来对其进行修复。 https://www.dotnetportal.cz/blogy/15/Null-Reference-Exception/5250/Digitalni-podepisovani-PDF-souboru-vC-cast-2

Answer 1

您需要的一切：

appearance.SetVisibleSignature("---> ExistSignatureName <-----");
MakeSignature.SignDetached(appearance, pks, chain, null, null, null, 0, CryptoStandard.CMS);

完整代码：

private static void SignPdf(string filename, string folderPdf, string pathToNewSignFile, string pathToCerts, string nameCert, string passCert)
{      
    var pathToCert = GetFullNameFile(pathToCerts, nameCert); //Oh.. I did not know about the Path.Combine function.

    if (!File.Exists(pathToCert))
    {
        logger.Error("Certificate not exist " + pathToCert);
        return;
    }

    var pass = passCert.ToCharArray();

    FileStream fs;
    try
    {
        fs = new FileStream(pathToCert, FileMode.Open);
    }
    catch (Exception ex)
    {
        logger.Error(ex, "Could not open cert" + pathToCert);
        return;
    }

    var store = new Pkcs12Store(fs, pass);

    fs.Close();

    var alias = "";

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

    var pk = store.GetKey(alias);

    ICollection<X509Certificate> chain = store.GetCertificateChain(alias).Select(c => c.Certificate).ToList();

    var parameters = pk.Key as RsaPrivateCrtKeyParameters;

    var pathPdf = GetFullNameFile(folderPdf, filename); //Oh.. I did not know about the Path.Combine function.

    var pathToSigPdf = GetFullNameFile(pathToNewSignFile, filename);

    if (!File.Exists(pathPdf))
    {
        logger.Error("Could not open file" + pathPdf + "  File not exist");
        return;
    }

    var reader = new PdfReader(pathPdf);


    FileStream fileStreamSigPdf;
    try
    {
        fileStreamSigPdf = new FileStream(pathToSigPdf, FileMode.Create);
    }
    catch (Exception ex)
    {
        logger.Error(ex, "Could not create file" + pathToSigPdf);
        return;
    }

    var stamper = PdfStamper.CreateSignature(reader, fileStreamSigPdf, '\0', null, true);

    var appearance = stamper.SignatureAppearance;
    appearance.Reason = "Утверждено";

    appearance.SetVisibleSignature("---> ExistSignatureName <-----");

    IExternalSignature pks = new PrivateKeySignature(parameters, DigestAlgorithms.SHA256);
    MakeSignature.SignDetached(appearance, pks, chain, null, null, null, 0, CryptoStandard.CMS);

    fileStreamSigPdf.Close();
    reader.Close();
    stamper.Close();

    logger.Info("Signed successfully " + filename);
}

我们公司有一个Web服务器。 1.获取哈希字段2.在加密插件的帮助下，我们对哈希签名3.将签名插入字段

第1步。

public string PrepareSignatureAndGetHash()
    {
        var hash = string.Empty;

        using (var reader = new PdfReader("PathTemplate"))
        {
            using (var fileStream = File.OpenWrite("PathToTemp"))
            {
                using (var stamper = PdfStamper.CreateSignature(reader, fileStream, '0', null, true))
                {
                    var signatureAppearance = stamper.SignatureAppearance;
                    signatureAppearance.SetVisibleSignature("ExistSignatureName");
                    IExternalSignatureContainer external = new ExternalBlankSignatureContainer(PdfName.ADOBE_PPKLITE, PdfName.ADBE_PKCS7_DETACHED);
                    signatureAppearance.Reason = "Sig";
                    signatureAppearance.Layer2Text = "Super SIG";

                    signatureAppearance.SignatureRenderingMode = PdfSignatureAppearance.RenderingMode.DESCRIPTION;

                    MakeSignature.SignExternalContainer(signatureAppearance, external, 8192);


                    using (var contentStream = signatureAppearance.GetRangeStream())
                    {
                        hash = string.Join(string.Empty, SHA1.Create().ComputeHash(contentStream).Select(x => x.ToString("X2")));
                    }
                }
            }
        }

    return hash;
}

第2步。

public void SigSignature(string base64String)
{
    using (var reader = new PdfReader("PathToTemp"))
    {
        using (var fileStream = File.OpenWrite("PathToSig"))
        {
            var byteSig = Convert.FromBase64String(base64String);
            IExternalSignatureContainer external = new MfuaExternalSignatureContainer(byteSig);

            MakeSignature.SignDeferred(reader, "ExistSignatureName", fileStream, external);
        }
    }
}

private class MfuaExternalSignatureContainer : IExternalSignatureContainer
{
    private readonly byte[] _signedBytes;

    public MfuaExternalSignatureContainer(byte[] signedBytes)
    {
        _signedBytes = signedBytes;
    }

    public byte[] Sign(Stream data)
    {
        return _signedBytes;
    }

    public void ModifySigningDictionary(PdfDictionary signDic)
    {
    }
}